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Agreement and Plan of Merger - Iron Mountain Inc. and Pierce Leahy Corp.

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                          AGREEMENT AND PLAN OF MERGER


                                 By and Between


                           IRON MOUNTAIN INCORPORATED

                                       and

                               PIERCE LEAHY CORP.

                                   dated as of

                                October 20, 1999






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                                TABLE OF CONTENTS
                                                                                                          

ARTICLE 1.        THE MERGER............................................................................1
                  Section 1.1.      The Merger..........................................................1
                  Section 1.2.      Action by Iron Mountain Stockholders and Pierce
                                    Leahy Shareholders..................................................2
                  Section 1.3.      Closing.............................................................2
                  Section 1.4.      Effective Time......................................................2
                  Section 1.5.      Effect of the Merger................................................3
                  Section 1.6.      Articles of Incorporation...........................................3
                  Section 1.7.      Bylaws..............................................................3
                  Section 1.8.      Directors and Officers..............................................3

ARTICLE 2.        CONVERSION OF SECURITIES; EXCHANGE OF CERTIFICATES....................................3
                  Section 2.1.      Conversion of Securities............................................3
                  Section 2.2.      Exchange of Certificates............................................4
                  Section 2.3.      Stock Transfer Books................................................5
                  Section 2.4.      Option Securities of Pierce Leahy...................................5
                  Section 2.5.      Option Securities of Iron Mountain..................................5

ARTICLE 3.        REPRESENTATIONS AND WARRANTIES OF PIERCE LEAHY........................................5
                  Section 3.1.      Organization and Business; Power and Authority;
                                    Effect of Transaction...............................................5
                  Section 3.2.      SEC Filings; Financial Statements...................................8
                  Section 3.3.      Changes in Condition................................................8
                  Section 3.4.      Liabilities.........................................................9
                  Section 3.5.      Title to Properties; Leases.........................................9
                  Section 3.6.      Compliance with Governmental Authorizations and
                                    Applicable Law......................................................9
                  Section 3.7.      Year 2000..........................................................10
                  Section 3.8.      Related Transactions...............................................10
                  Section 3.9.      Tax Matters........................................................10
                  Section 3.10.     ERISA..............................................................11
                  Section 3.11.     Authorized and Outstanding Capital Stock...........................13
                  Section 3.12.     Employment Arrangements............................................14
                  Section 3.13.     Material Agreements................................................15
                  Section 3.14.     Ordinary Course of Business........................................15
                  Section 3.15.     Broker or Finder...................................................16
                  Section 3.16.     Environmental Matters..............................................17
                  Section 3.17.     Board Action; Fairness Opinion.....................................17
                  Section 3.18.     Materiality........................................................17

ARTICLE 4.        REPRESENTATIONS AND WARRANTIES OF IRON MOUNTAIN......................................18
                  Section 4.1.      Organization and Business; Power and Authority;
                                    Effect of Transaction..............................................18
                  Section 4.2.      SEC Filings; Financial Statements..................................20
                  Section 4.3.      Changes in Condition...............................................21
                  Section 4.4.      Liabilities........................................................21
                  Section 4.5.      Title to Properties; Leases........................................21


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                                       ii

                  Section 4.6.      Compliance with Governmental Authorizations and
                                    Applicable Law.....................................................22
                  Section 4.7.      Year 2000..........................................................22
                  Section 4.8.      Related Transactions...............................................22
                  Section 4.9.      Tax Matters........................................................23
                  Section 4.10.     ERISA..............................................................24
                  Section 4.11.     Authorized and Outstanding Capital Stock...........................25
                  Section 4.12.     Employment Arrangements............................................27
                  Section 4.13.     Material Agreements................................................27
                  Section 4.14.     Ordinary Course of Business........................................28
                  Section 4.15.     Broker or Finder...................................................29
                  Section 4.16.     Environmental Matters..............................................29
                  Section 4.17.     Board Action; Fairness Opinion.....................................29
                  Section 4.18.     Materiality........................................................30

ARTICLE 5.        ADDITIONAL COVENANTS.................................................................30
                  Section 5.1.      Access to Information; Confidentiality.............................30
                  Section 5.2.      Conduct of the Business of Pierce Leahy Pending the Merger.........30
                  Section 5.3.      Conduct of the Business of Iron Mountain Pending
                                    the Merger.........................................................32
                  Section 5.4.      Control of Operations..............................................34
                  Section 5.5.      Agreement to Cooperate.............................................34
                  Section 5.6.      Affiliate Agreements; Registration Rights Agreement................35
                  Section 5.7.      No Solicitation....................................................36
                  Section 5.8.      Directors' and Officers' Indemnification and Insurance.............38
                  Section 5.9.      Notification of Certain Matters....................................39
                  Section 5.10.     Public Announcements...............................................39
                  Section 5.11.     Certain Actions Concerning Business Combinations...................40
                  Section 5.12.     Option Securities..................................................40
                  Section 5.13.     Tax Treatment......................................................40
                  Section 5.14.     Registration Statement and Joint Proxy Statement/Prospectus........40
                  Section 5.15.     Exchange Listing...................................................42
                  Section 5.16.     Disclosure Schedules...............................................42
                  Section 5.17.     Pierce Leahy Indebtedness..........................................42
                  Section 5.18.     Pierce Leahy Command Company.......................................43
                  Section 5.19.     Stock Dividend.....................................................43
                  Section 5.20.     Pierce Leahy Shareholders' Agreement...............................43
                  Section 5.21.     Termination of Plans...............................................43

ARTICLE 6.        CLOSING CONDITIONS...................................................................44
                  Section 6.1.      Conditions to Obligations of Each Party to Effect the Merger.......44
                  Section 6.2.      Conditions to Obligations of Iron Mountain. .......................45
                  Section 6.3.      Conditions to Obligations of Pierce Leahy..........................46

ARTICLE 7.        TERMINATION, AMENDMENT AND WAIVER....................................................46
                  Section 7.1.      Termination........................................................46
                  Section 7.2.      Effect of Termination..............................................48


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                                       iii

                  Section 7.3.      Amendment..........................................................48
                  Section 7.4.      Waiver.............................................................49
                  Section 7.5.      Fees, Expenses and Other Payments..................................49
                  Section 7.6.      Effect of Investigation............................................50

ARTICLE 8.        GENERAL PROVISIONS...................................................................50
                  Section 8.1.      Nonsurvival of Representations and Warranties......................50
                  Section 8.2.      Notices............................................................50
                  Section 8.3.      Headings...........................................................51
                  Section 8.4.      Severability.......................................................51
                  Section 8.5.      Entire Agreement...................................................51
                  Section 8.6.      Assignment.........................................................51
                  Section 8.7.      Parties in Interest................................................52
                  Section 8.8.      Governing Law......................................................52
                  Section 8.9.      Enforcement of the Agreement.......................................52
                  Section 8.10.     Counterparts.......................................................52
                  Section 8.11.     Mutual Drafting....................................................52

ARTICLE 9.        DEFINITIONS..........................................................................52


The   following   exhibits  and   schedules   have  been  omitted  and  will  be
supplementally filed with the Commission upon request:

EXHIBITS

         1.6               Form of Amended and Restated Articles of Incorporation
         1.7               Form of Amended and Restated Bylaws
         5.6(a)            Form of Affiliate Agreement
         5.6(b)            Form of Registration Rights Agreement Joinder
         6.2(e)            Form of Employment Agreement

SCHEDULES

         Pierce Leahy Disclosure Schedule
         Iron Mountain Disclosure Schedule



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                          AGREEMENT AND PLAN OF MERGER


         AGREEMENT  AND PLAN OF MERGER,  dated as of October  20,  1999,  by and
between Iron Mountain  Incorporated,  a Delaware  corporation ("Iron Mountain"),
and Pierce Leahy Corp., a Pennsylvania corporation ("Pierce Leahy").

                              W I T N E S S E T H:

         WHEREAS, upon the terms and subject to the conditions of this Agreement
(this and other  capitalized  terms used herein are either  defined in Article 9
below or in  another  Article of this  Agreement  and,  in such case,  Article 9
includes  a  reference  to  such  Section),   in  accordance  with  the  General
Corporation  Law of the State of  Delaware  (the  "DGCL")  and the  Pennsylvania
Business Corporation Law of 1988, as amended (the "PBCL"), Pierce Leahy and Iron
Mountain  will carry out a business  combination  transaction  pursuant to which
Iron Mountain will merge with and into Pierce Leahy (the "Merger");

         WHEREAS,  the  Board of  Directors  of  Pierce  Leahy  has  unanimously
determined that the Merger and and the Transactions are in the best interests of
Pierce  Leahy  and  the   shareholders   of  Pierce  Leahy  (the  "Pierce  Leahy
Shareholders") and has approved and adopted this Agreement as a tax-free plan of
reorganization  within the provisions of Section 368(a) of the Internal  Revenue
Code of 1986, as amended (the "Code"),  has approved this Agreement,  the Merger
and  the  Transactions  and  has  recommended  approval  and  adoption  of  this
Agreement, the Merger and the Transactions by the Pierce Leahy Shareholders; and

         WHEREAS,  the  Board of  Directors  of Iron  Mountain  has  unanimously
determined that the Merger and the Transactions are advisable to and in the best
interests  of, Iron  Mountain and the  stockholders  of Iron Mountain (the "Iron
Mountain  Stockholders")  and has  approved  and  adopted  this  Agreement  as a
tax-free plan of  reorganization  within the provisions of Section 368(a) of the
Code,  has approved  this  Agreement,  the Merger and the  Transactions  and has
recommended  approval  and  adoption  of  this  Agreement,  the  Merger  and the
Transactions by the Iron Mountain Stockholders.

         NOW,  THEREFORE,  in  consideration of the foregoing and the respective
representations,   warranties,  covenants  and  agreements  set  forth  in  this
Agreement, the parties hereto, intending to be legally bound, agree as follows:

                                   ARTICLE 1.

                                   THE MERGER

         Section 1.1. The Merger.  Upon the terms and subject to the  conditions
set forth in this  Agreement,  and in accordance  with the DGCL and the PBCL, at
the Effective Time Iron Mountain shall be merged with and into Pierce Leahy.  As
a result of the Merger,  the separate existence of Iron Mountain shall cease and
Pierce  Leahy shall  continue as the  surviving  corporation  of the Merger (the
"Surviving Corporation").



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                                        2

         Section  1.2.  Action by Iron  Mountain  Stockholders  and Pierce Leahy
Shareholders.

         (a) Pierce  Leahy,  acting  through its Board of Directors,  shall,  in
accordance  with and subject to  Applicable  Law, its Organic  Documents and the
rules of the NYSE: as soon as  practicable,  duly call,  give notice of, convene
and hold a special meeting of the Pierce Leahy  Shareholders  for the purpose of
adopting  and  approving  this  Agreement,   the  Merger  and  the  Transactions
(including any adjournment thereof, the "Pierce Leahy Special Meeting"); include
in the Joint Proxy Statement/Prospectus the conclusion and recommendation of the
Board of Directors to the effect that the Board of Directors,  having determined
that this Agreement,  the Merger and the  Transactions are in the best interests
of Pierce Leahy and the Pierce Leahy Shareholders,  has approved this Agreement,
the  Merger  and  the   Transactions   and  recommends  that  the  Pierce  Leahy
Shareholders  vote in favor of the approval and adoption of this Agreement,  the
Merger and the  Transactions;  and use its reasonable best efforts to obtain the
necessary  approval  and  adoption  of  this  Agreement,   the  Merger  and  the
Transactions by the Pierce Leahy Shareholders.

         (b) Iron  Mountain,  acting through its Board of Directors,  shall,  in
accordance  with and subject to  Applicable  Law, its Organic  Documents and the
rules of the NYSE: as soon as  practicable,  duly call,  give notice of, convene
and hold a special meeting of the Iron Mountain  Stockholders for the purpose of
adopting  and  approving  this  Agreement,   the  Merger  and  the  Transactions
(including any adjournment  thereof,  the "Iron Mountain  Special  Meeting" and,
together with the Pierce Leahy Special Meeting, the "Special Meetings"); include
in the Joint Proxy Statement/Prospectus the conclusion and recommendation of the
Board of Directors to the effect that the Board of Directors,  having determined
that this Agreement, the Merger and the Transactions are advisable to and in the
best interests of Iron Mountain and the Iron Mountain Stockholders, has approved
this  Agreement,  the Merger and the  Transactions  and recommends that the Iron
Mountain  Stockholders  vote in  favor  of the  approval  and  adoption  of this
Agreement, the Merger and the Transactions;  and use its reasonable best efforts
to obtain the necessary approval and adoption of this Agreement,  the Merger and
the Transactions by the Iron Mountain Stockholders.

         Section 1.3. Closing.  Unless this Agreement shall have been terminated
pursuant to Section 7.1 hereof,  the closing of the Merger (the  "Closing") will
take place at 10:00 A.M.,  local time,  on the fifth  business day (the "Closing
Date") after the date on which the last of the conditions set forth in Article 6
is  satisfied  or waived  (other than  conditions  requiring  deliveries  at the
Closing),  at the offices of Sullivan & Worcester  LLP, One Post Office  Square,
Boston,  Massachusetts,  unless  another  date,  time or place is  agreed  to in
writing by Pierce Leahy and Iron Mountain;  provided, however, that, without the
consent of Pierce Leahy and Iron Mountain, the Closing Date shall not be earlier
than January 15, 2000.

         Section  1.4.  Effective  Time.  As promptly as  practicable  after the
satisfaction or, if permissible, waiver of the conditions set forth in Article 6
(but  subject to Section 1.3 hereof),  the Parties  shall cause the Merger to be
consummated by filing a certificate of merger with the Secretary of State of the
State of Delaware  and  articles of merger  with the  Secretary  of State of the
Commonwealth of  Pennsylvania,  and by making any related filings required under
the DGCL and the PBCL.  The Merger shall become  effective at such time (but not
prior to the  Closing  Date) as the  later  to occur of the due  filing  of such
certificate with the Secretary of State of the State of Delaware


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                                        3

and the  due  filing  of such  articles  with  the  Secretary  of  State  of the
Commonwealth  of  Pennsylvania,  or at such later time on the Closing Date as is
specified in such certificate and articles (the "Effective Time").

         Section 1.5.  Effect of the Merger.  From and after the Effective Time,
the Surviving Corporation shall possess all the rights,  privileges,  powers and
franchises and be subject to all of the restrictions, disabilities and duties of
Pierce Leahy and Iron Mountain,  and the Merger shall otherwise have the effect,
as provided under the DGCL and the PBCL.

         Section 1.6.  Articles of  Incorporation.  At the Effective  Time,  the
Articles of  Incorporation  of the  Surviving  Corporation  shall be amended and
restated  in their  entirety  to read as set forth in Exhibit 1.6 hereto and the
name of the Surviving Corporation shall be Iron Mountain Incorporated.

         Section 1.7. Bylaws. At the Effective Time, the Bylaws of the Surviving
Corporation shall be amended and restated in their entirety to read as set forth
in Exhibit 1.7 hereto.

         Section 1.8. Directors and Officers. From and after the Effective Time,
until  successors  are duly elected or appointed and qualified (or their earlier
resignation or removal) in accordance  with Applicable Law, the officers of Iron
Mountain  shall be the  officers of the  Surviving  Corporation  (except that J.
Peter Pierce shall be the  President of the Surviving  Corporation  and David S.
Wendell shall be the Senior Vice President of the Surviving Corporation). Pierce
Leahy's  Board of  Directors  shall  take all  necessary  corporate  actions  to
increase the number of directors of the Surviving Corporation to eleven (11) and
shall nominate the directors of Iron Mountain  together with J. Peter Pierce and
Howard D. Ross,  subject to the approval of the Pierce Leahy Shareholders at the
Pierce Leahy Special  Meeting,  to serve at the Effective Time as the members of
the Board of Directors of the  Surviving  Corporation.  At the  Effective  Time,
subject to the approval of the Pierce Leahy Shareholders,  Iron Mountain's Class
A, B and C directors  shall be Class II, III and I directors,  respectively,  of
the Surviving  Corporation and J. Peter Pierce shall be an additional  Class III
Director of the Surviving  Corporation and Howard D. Ross shall be an additional
Class  II  Director  of the  Surviving  Corporation,  each  to  hold  office  in
accordance  with the  Articles  of  Incorporation  and  Bylaws of the  Surviving
Corporation. At the Effective Time, Leo W. Pierce, Sr. shall be appointed as the
Chairman Emeritus of the Surviving Corporation.

                                   ARTICLE 2.

               CONVERSION OF SECURITIES; EXCHANGE OF CERTIFICATES

         Section 2.1. Conversion of Securities. At the Effective Time, by virtue
of the Merger and without any action on the part of Iron Mountain,  Pierce Leahy
or the holders of any of the following securities:

         (a) Each share of Common  Stock,  par value  $.01 per share,  of Pierce
Leahy (the "Pierce Leahy Common  Stock")  outstanding  immediately  prior to the
Effective Time shall remain outstanding.



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                                        4

         (b) Each  share of Series A  Redeemable  Senior  Pay-in-Kind  Preferred
Stock,  par value $.01 per share,  of Pierce Leahy (the "Pierce Leahy  Preferred
Stock")  outstanding  immediately  prior  to the  Effective  Time  shall  remain
outstanding.

         (c) Each  share of Common  Stock,  par value  $.01 per  share,  of Iron
Mountain (the "Iron Mountain Common Stock") outstanding immediately prior to the
Effective Time shall, by virtue of the Merger and without any action on the part
of the holder thereof,  be converted into one fully paid and nonassessable share
of Pierce Leahy Common Stock. At the Effective Time, all shares of Iron Mountain
Common Stock shall no longer be outstanding and shall automatically be cancelled
and retired. Certificates previously representing shares of Iron Mountain Common
Stock  outstanding  immediately  prior to the Effective Time shall be deemed for
all purposes to represent an equivalent  number of shares of Pierce Leahy Common
Stock following the Effective Time and shall be so accepted for such purposes by
the Surviving Corporation.

         (d)  Notwithstanding any provision to the contrary in this Section 2.1,
each share of Iron Mountain  Common Stock held in the treasury of Iron Mountain,
each share of Iron Mountain Common Stock owned by Pierce Leahy or any Subsidiary
of Pierce  Leahy,  and each  share of Pierce  Leahy  Common  Stock  held by Iron
Mountain or any Subsidiary of Iron Mountain  immediately  prior to the Effective
Time shall  automatically be cancelled and  extinguished  without any conversion
thereof and no payment shall be made with respect thereto.

         Section 2.2.      Exchange of Certificates.

         (a) To the extent  the  Parties or the  Surviving  Corporation  deem it
necessary or appropriate  to permit or facilitate  transfers of the Common Stock
of the Surviving Corporation following the Effective Time, the Parties shall use
their  reasonable  best efforts to agree on customary  exchange  procedures  for
certificates  representing  shares of Pierce Leahy Common Stock or Iron Mountain
Common Stock, as the need may be, to be exchanged for certificates  representing
shares of common stock of the Surviving Corporation.  The Parties shall agree no
later than twenty (20) days before the Closing Date on such exchange  procedures
and appoint an exchange  agent (the "Exchange  Agent") to exchange  certificates
representing  shares of Pierce Leahy Common Stock or Iron Mountain Common Stock,
as the need may be, outstanding  immediately prior to the Effective Time for new
certificates representing shares of common stock of the Surviving Corporation as
soon as practicable after the Effective Time.

         (b)  To  the  extent  necessary,  if an  Exchange  Agent  has  been  so
appointed,  as soon as  reasonably  practicable  after the Effective  Time,  the
Surviving  Corporation will instruct the Exchange Agent to issue (by mail to the
most recent address of such holder as shown on the Surviving Corporation's books
and records) to the holders of certificates  to be exchanged  (other than shares
to be  canceled  pursuant  to  Section  2.1(d)),  a letter  of  transmittal  and
instructions  to effect the  surrender  of such  certificates  in  exchange  for
replacement certificates.

         (c) None of Iron Mountain,  Pierce Leahy, the Surviving  Corporation or
the  Exchange  Agent  shall be  liable to any  holder of shares of Pierce  Leahy
Common Stock or Iron Mountain Common Stock for any shares of common stock of the
Surviving  Corporation delivered to a public official pursuant to any applicable
abandoned property, escheat or similar law.



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                                        5

         Section 2.3. Stock  Transfer  Books.  At the Effective  Time, the stock
transfer books of Iron Mountain  shall be closed,  and there shall be no further
registration of transfers of shares of Iron Mountain Common Stock  thereafter on
the records of Iron  Mountain.  Shares of Iron  Mountain  Common Stock that have
been  converted  into shares of Pierce Leahy  Common  Stock  pursuant to Section
2.1(c)  shall be deemed  outstanding  shares of Pierce Leahy Common Stock on and
after the Effective Time.

         Section 2.4. Option  Securities of Pierce Leahy.  Each unexpired option
to  purchase  Pierce  Leahy  Common  Stock  ("Pierce  Leahy  Options")  that  is
outstanding at the Effective Time shall remain outstanding.

         Section 2.5.  Option  Securities of Iron Mountain.  Effective as of the
Effective  Time, each then  outstanding  option to purchase Iron Mountain Common
Stock (the "Iron Mountain Options") granted pursuant to the Iron Mountain Option
Plans shall be converted automatically into an option to purchase such number of
shares  of  Pierce  Leahy  Common  Stock  equal to the  number of shares of Iron
Mountain Common Stock subject to such Iron Mountain Option  immediately prior to
the  Effective  Time and on  other  terms  and  conditions  (including,  without
limitation,  exercise  price)  as were  applicable  under  the  applicable  Iron
Mountain Option Plan and the underlying stock option agreement. At the Effective
Time, the Surviving  Corporation  shall assume each of the Iron Mountain  Option
Plans and each  underlying  stock option  agreement  that relates to outstanding
Iron Mountain Options. The Surviving  Corporation shall (i) reserve for issuance
the number of  additional  shares of Pierce  Leahy Common Stock that will become
issuable upon the exercise of the Iron Mountain  Options,  as so converted,  and
(ii) as soon as practicable  after the Effective Time, have filed a Registration
Statement  on Form S-8 to  register  the  shares of Pierce  Leahy  Common  Stock
subject to such Iron Mountain Options, as so converted.

                                   ARTICLE 3.

                 REPRESENTATIONS AND WARRANTIES OF PIERCE LEAHY

         Pierce  Leahy  hereby  represents  and  warrants  to Iron  Mountain  as
follows:

         Section 3.1. Organization and Business; Power and Authority;  Effect of
Transaction.

         (a)      Pierce Leahy:

                  (i) is a corporation  duly organized and subsisting  under the
         laws of the Commonwealth of Pennsylvania,

                  (ii) has all requisite corporate power and corporate authority
         to own or hold under lease its  properties and to conduct its business,
         and has in full force and effect all  Governmental  Authorizations  and
         Private  Authorizations and has made all Governmental  Filings,  to the
         extent  required  for such  ownership  and  lease of its  property  and
         conduct of its business, except to the extent the failure to be in full
         force and effect or to have made such  Governmental  Filings would not,
         individually  or in the  aggregate,  reasonably  be expected to have an
         Adverse Effect, and



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                                        6

                  (iii) is duly  qualified and  authorized to do business and is
         in good standing as a foreign corporation in each jurisdiction in which
         the  character  of its  property  or the  nature  of  its  business  or
         operations requires such qualification or authorization,  except to the
         extent the  failure to so qualify or to  maintain  such  authorizations
         would not reasonably be expected to have an Adverse Effect.

         (b)  Pierce  Leahy has all  requisite  corporate  power  and  corporate
authority to execute and deliver,  and to perform its  obligations  under,  this
Agreement and each Collateral Document executed or required to be executed by it
pursuant  hereto or thereto and to consummate  the Merger and the  Transactions,
and  the  execution,  delivery  and  performance  of  this  Agreement  and  each
Collateral Document executed or required to be executed by it pursuant hereto or
thereto have been duly authorized by all requisite  corporate action (other than
that of the Pierce Leahy  Shareholders).  This  Agreement has been duly executed
and  delivered by Pierce Leahy and  constitutes,  and each  Collateral  Document
executed or  required  to be  executed  by it  pursuant  hereto or thereto or to
consummate  the Merger and the  Transactions,  when  executed  and  delivered by
Pierce Leahy or a Pierce Leahy  Shareholder  will constitute,  legal,  valid and
binding   obligations  of  Pierce  Leahy  or  such  Pierce  Leahy   Shareholder,
enforceable  in  accordance  with  their  respective   terms,   except  as  such
enforceability   may  be  subject   to   bankruptcy,   moratorium,   insolvency,
reorganization,  arrangement,  voidable  preference,  fraudulent  conveyance and
other  similar laws  relating to or affecting the rights of creditors and except
as the same may be subject to the effect of general  principles  of equity  (the
"Enforceability Exceptions").  The affirmative vote of the holders of a majority
of the  outstanding  shares of Pierce Leahy  Common  Stock  present or voting by
proxy at the Pierce  Leahy  Special  Meeting at which a quorum is present is the
only vote of the holders of any class or series of the  capital  stock of Pierce
Leahy necessary to approve this Agreement, the Merger and the Transactions under
Applicable Law and Pierce Leahy's Organic  Documents.  The provisions of Section
2538 and Sections  2551-2556 of the PBCL will not apply to this  Agreement,  the
Merger or the Transactions.

         (c)  Except  as  set  forth  in  Section  3.1(c)  of the  Pierce  Leahy
Disclosure  Schedule  (which in accordance  with Section 5.16 hereof (other than
those  sections  relating to  Applicable  Law,  Organic  Documents  and Material
Agreements,  which  sections  shall be  delivered  herewith),  will be delivered
within thirty (30) days after the date of this Agreement), neither the execution
and delivery of this Agreement or any Collateral  Document  executed or required
to be  executed  pursuant  hereto  or  thereto,  nor  the  consummation  of  the
Transactions, nor compliance with the terms, conditions and provisions hereof or
thereof by Pierce Leahy:

                  (i) will conflict with, or result in a breach or violation of,
         or constitute a default under, any Applicable Law on the part of Pierce
         Leahy or any Pierce Leahy  Subsidiary or will conflict  with, or result
         in a breach or violation of, or constitute a default  under,  or permit
         the  acceleration  of any  obligation  or liability  in, or but for any
         requirement  of  giving  of notice  or  passage  of time or both  would
         constitute  such a conflict  with,  breach or violation  of, or default
         under, or permit any such  acceleration in, any Organic Document or any
         Contractual  Obligation of Pierce Leahy or any Pierce Leahy Subsidiary,
         other than any such  conflict,  breach,  violation  or default as would
         not,  individually or in the aggregate,  reasonably be expected to have
         an Adverse Effect;



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                                        7

                  (ii) will result in or permit the  creation or  imposition  of
         any Lien upon any  property  now owned or leased by Pierce Leahy or any
         Pierce Leahy Subsidiary, except for such Liens that, individually or in
         the  aggregate,  would not  reasonably  be  expected to have an Adverse
         Effect; or

                  (iii)  will   require  any   Governmental   Authorization   or
         Governmental   Filing  or   Private   Authorization,   except  for  the
         certificate  and articles of merger and related  filings under the DGCL
         and the PBCL in  connection  with the Merger and the  Transactions  and
         except pursuant to the HSR Act, the Exchange Act, the Securities Act or
         any  applicable  state  securities  laws,  or as  otherwise  would  not
         reasonably be expected to have an Adverse Effect.

         (d) Pierce  Leahy does not have any  Subsidiaries  other than those set
forth on Section 3.1(d) of the Pierce Leahy Disclosure  Schedule,  each of which
is directly or indirectly wholly owned (except as set forth in Section 3.1(d) of
the Pierce Leahy  Disclosure  Schedule),  is an Entity which is duly  organized,
validly  existing  and in  good  standing  under  the  laws  of  the  respective
jurisdiction  of  organization  set forth opposite its name on Section 3.1(d) of
the Pierce Leahy Disclosure Schedule, and is duly qualified and in good standing
in each other  jurisdiction in which the character of its property or the nature
of its business or  operations  requires  such  qualification  or  authorization
(except to the extent the failure to be duly organized,  validly  existing or in
good  standing or to so qualify  would not,  individually  or in the  aggregate,
reasonably  be  expected  to have an Adverse  Effect),  with full  corporate  or
similar  power and  corporate  or similar  authority to carry on the business in
which it is engaged.  Except as set forth in Section  3.1(d) to the Pierce Leahy
Disclosure  Schedule,  each Pierce Leahy Subsidiary has in full force and effect
all Governmental  Authorizations  and Private  Authorizations,  and has made all
Governmental  Filings to the extent required for such ownership and lease of its
property  and  conduct of its  business,  except to the extent the failure to so
have  such   Authorizations  or  made  such  Governmental   Filings  would  not,
individually  or in the  aggregate,  reasonably  be  expected to have an Adverse
Effect.  Except to the extent set forth on  Section  3.1(d) of the Pierce  Leahy
Disclosure  Schedule,  Pierce Leahy owns,  directly or indirectly  through other
Pierce Leahy Subsidiaries,  all of the outstanding capital stock or other equity
interests (as shown on Section 3.1(d) of the Pierce Leahy  Disclosure  Schedule)
of each Pierce Leahy Subsidiary, free and clear of all Liens, and all such stock
or other equity  interests have been duly  authorized and validly issued and are
fully paid and  nonassessable  and were issued and sold in  compliance  with the
Securities Act, the Exchange Act and applicable state securities laws. Except as
set forth in Section 3.1(d) of the Pierce Leahy Disclosure  Schedule,  (i) there
is neither  outstanding nor has any Pierce Leahy  Subsidiary  agreed to grant or
issue any shares of its capital  stock or other  equity  interests or any Option
Security or Convertible Security, and (ii) no Pierce Leahy Subsidiary is a party
to or is bound  by any  agreement,  put or  commitment  pursuant  to which it is
obligated to purchase,  redeem or otherwise  acquire any shares of capital stock
or other equity interests or any Option Security or Convertible Security.

         (e)  Pierce  Leahy  does not own any  capital  stock or equity or other
interest in any other Entity or enterprise,  however  organized and however such
interest may be denominated or evidenced,  except as set forth in Section 3.1(d)
or 3.1(e) of the Pierce Leahy Disclosure Schedule.



<PAGE>


                                        8

         Section 3.2.      SEC Filings; Financial Statements.

         (a) Pierce Leahy has filed all forms, reports and documents required to
be filed by it with the SEC, and has heretofore made available to Iron Mountain,
in the form filed with the SEC (including any exhibits thereto),  (i) its Annual
Report on Form 10-K for the  fiscal  year  ended  December  31,  1998,  (ii) its
Quarterly  Reports on Form 10-Q for the  quarters  ended March 31, 1999 and June
30,  1999,   (iii)  its  proxy  statement   relating  to  its  1999  meeting  of
shareholders,  (iv) all of its registration  statements that are effective as of
the date of this  Agreement  under which shares of Pierce Leahy Common Stock are
still  available  for issuance (a complete list of which is set forth in Section
3.2(a) of the  Pierce  Leahy  Disclosure  Schedule),  and (v) all  other  forms,
reports and  registration  statements  filed by it with the SEC since January 1,
1999 (the forms, reports and other documents referred to in clauses (i), through
(v) above,  together with all other forms, reports and documents filed by Pierce
Leahy with the SEC, being referred to herein  collectively  as the "Pierce Leahy
SEC  Reports").  The Pierce  Leahy SEC Reports and any forms,  reports and other
documents  filed by Pierce Leahy with the SEC after the date of this  Agreement,
(x) complied with or will comply in all material  respects with the requirements
of the  Securities  Act and the Exchange  Act, as the case may be, and the rules
and regulations  thereunder and (y) did not at the time they were filed, or will
not at the time they are filed,  contain any untrue statement of a material fact
or omit to state a material fact  required to be stated  therein or necessary in
order to make the  statements  made therein,  in the light of the  circumstances
under which they were made, not misleading;  provided that no  representation or
warranty is made with respect to any information  provided by Iron Mountain that
is or will be included in any Pierce  Leahy SEC Report.  None of Pierce  Leahy's
Subsidiaries is required to file any forms,  reports or other documents with the
SEC pursuant to Section 12 or 15 of the Exchange Act.

         (b) Pierce  Leahy's  financial  statements,  including in each case the
notes  thereto,  contained in its Annual Report on Form 10-K for the fiscal year
ended December 31, 1998 and its Quarterly  Reports on Form 10-Q for the quarters
ended March 31, 1999 and June 30, 1999 (the "Pierce Leahy Financial Statements")
(i) have been prepared from,  and are in accordance  with, the books and records
of Pierce Leahy and its consolidated  Subsidiaries,  (ii) comply in all material
respects with applicable  accounting  requirements  and with published rules and
regulations  of the SEC with  respect  thereto,  (iii)  have  been  prepared  in
accordance  with GAAP  applied on a  consistent  basis  throughout  the  periods
covered  thereby,  except as  otherwise  noted  therein,  are true,  correct and
complete,  and (iv)  fairly  present  the  financial  condition  and  results of
operations  and cash flows of Pierce  Leahy and its  Subsidiaries,  on the bases
therein  stated,  as of the  respective  dates  thereof,  and for the respective
periods covered thereby subject, in the case of unaudited  financial  statements
to normal nonmaterial year-end audit adjustments and accruals and to the absence
of complete footnotes.

         Section 3.3.  Changes in  Condition.  Since the date of the most recent
financial  statements  forming  part of the Pierce Leahy  Financial  Statements,
except to the extent  specifically  described in Section 3.3 of the Pierce Leahy
Disclosure Schedule, there has been no Adverse Change in Pierce Leahy. To Pierce
Leahy's  knowledge,  there is no Event  known to Pierce  Leahy  which  Adversely
Affects,  or would reasonably be expected to Adversely Affect,  Pierce Leahy and
its  Subsidiaries,  taken as a whole,  or the ability of Pierce Leahy to perform
any of the  obligations  set forth in this Agreement or any Collateral  Document
executed or required to be executed pursuant hereto or thereto.


<PAGE>


                                        9


         Section 3.4.  Liabilities.  (i) At the date of the most recent  balance
sheet  forming part of the Pierce Leahy  Financial  Statements,  neither  Pierce
Leahy nor any  Pierce  Leahy  Subsidiary  had any  obligations  or  liabilities,
accrued or unaccrued, fixed, absolute,  contingent or other (including,  without
limitation,  any contingent  payments or "earnouts"  owing under any acquisition
agreement), except as disclosed in such balance sheet, or the notes thereto, and
(ii) since such date,  neither Pierce Leahy nor any Pierce Leahy  Subsidiary has
incurred any such  obligations or liabilities,  other than those incurred in the
ordinary  course of business  consistent  with past practice of Pierce Leahy and
Pierce Leahy  Subsidiaries,  and other than obligations and liabilities which in
the case of clauses (i) and (ii) do not and, to Pierce Leahy's knowledge,  would
not,  individually  or in the  aggregate,  reasonably  be expected to  Adversely
Affect Pierce Leahy, except to the extent set forth in Section 3.4 of the Pierce
Leahy Disclosure Schedule.  Neither Pierce Leahy nor any Pierce Leahy Subsidiary
has guaranteed or is otherwise primarily or secondarily liable in respect of any
obligation or liability of any other Person (other than Pierce Leahy or a Pierce
Leahy Subsidiary), except for endorsements of negotiable instruments for deposit
in the  ordinary  course of  business,  consistent  with prior  practice,  or as
disclosed in the most recent balance sheet,  or the notes thereto,  forming part
of the Pierce Leahy  Financial  Statements or in Section 3.4 of the Pierce Leahy
Disclosure Schedule.

         Section  3.5.  Title  to  Properties;   Leases.  Except  as  would  not
reasonably be expected to have an Adverse Effect on Pierce Leahy, each of Pierce
Leahy and its Subsidiaries has good legal,  marketable and insurable title, with
respect to all real property  owned (in fee simple),  good title with respect to
all real property leased (in leasehold) reflected as an asset on the most recent
balance sheet forming part of the Pierce Leahy Financial Statements,  or held by
Pierce  Leahy  or  any  such  Subsidiary  for  use in  its  business,  if not so
reflected,  and good  indefeasible and  merchantable  title to all other assets,
tangible and intangible, reflected on the most recent balance sheet forming part
of the Pierce Leahy Financial Statements, or (excluding leased real estate) held
by Pierce Leahy or any Pierce Leahy Subsidiary for use in its business if not so
reflected,  or  purported  to have been  acquired by Pierce  Leahy or any Pierce
Leahy  Subsidiary  since  such  date,  except  inventory  sold or  depleted,  or
property, plant and other equipment used up or retired, since such date, in each
case in the ordinary  course of business  consistent  with the past  practice of
Pierce Leahy and its Subsidiaries, free and clear of all Liens, except (i) Liens
reflected  in the Pierce  Leahy  Financial  Statements,  (ii) Liens set forth on
Section 3.5(a) of the Pierce Leahy Disclosure  Schedule,  (iii) Permitted Liens,
and (iv) such Liens that do not or would not,  individually or in the aggregate,
reasonably be expected to have an Adverse Effect on Pierce Leahy.  Each Lease or
other  occupancy or other agreement under which Pierce Leahy or any Pierce Leahy
Subsidiary holds real or personal  property has been duly  authorized,  executed
and  delivered  by Pierce  Leahy or a Pierce  Leahy  Subsidiary,  and, to Pierce
Leahy's  knowledge,  by each of the other parties thereto;  each such Lease is a
legal,  valid  and  binding  obligation  of  Pierce  Leahy  or  a  Pierce  Leahy
Subsidiary,  and, to Pierce  Leahy's  knowledge,  of each other  party  thereto,
enforceable  in  accordance  with  its  terms  (subject  to  the  Enforceability
Exceptions), except where the lack of such authorization,  execution or delivery
or the lack of the legal,  valid and binding nature of such obligation would not
reasonably be expected to have an Adverse Effect on Pierce Leahy.

         Section 3.6. Compliance with Governmental Authorizations and Applicable
Law.

         (a) Section 3.6(a) of the Pierce Leahy Disclosure  Schedule  contains a
description  of all Legal Actions which are pending in which Pierce Leahy or any
Pierce Leahy Subsidiary is a party,


<PAGE>


                                       10

or to which the  businesses,  operations  or  properties  of Pierce Leahy or any
Pierce Leahy Subsidiary are subject or, to Pierce Leahy's  knowledge,  which are
threatened in writing  against,  Pierce Leahy or any Pierce Leahy  Subsidiary or
any  of  their   respective   businesses,   operations  or  properties,   which,
individually  or in the  aggregate,  if determined  against  Pierce Leahy or any
Pierce Leahy  Subsidiary  would reasonably be expected to have an Adverse Effect
on Pierce Leahy.

         (b) Pierce Leahy and its  Subsidiaries  have obtained all  Governmental
Authorizations  which are necessary for the ownership or use of their respective
properties  and the conduct of their  respective  businesses as now conducted by
Pierce Leahy or any Pierce Leahy Subsidiary and such Governmental Authorizations
are in full force and effect, except for such Governmental Authorizations which,
if not obtained and maintained in full force and effect,  would singly or in the
aggregate,  reasonably  be expected to have an Adverse  Effect on Pierce  Leahy.
Neither  Pierce Leahy nor any Pierce Leahy  Subsidiary is in material  breach or
violation of, or in default in the  performance,  observance or fulfillment  of,
any Governmental Authorization or any Applicable Law, and no Event exists or has
occurred,  which constitutes,  or but for any requirement of giving of notice or
passage of time or both would constitute,  such a breach,  violation or default,
under any  Governmental  Authorization  or any Applicable  Law,  except for such
breaches,  violations  or defaults as do not and, to Pierce  Leahy's  knowledge,
would not,  individually or in the aggregate,  reasonably be expected to have an
Adverse Effect on Pierce Leahy.

         Section  3.7.  Year  2000.  Any  inability  of Pierce  Leahy's  and its
Subsidiaries' systems (including,  without limitation, any Year 2000 Systems) to
properly recognize and process date sensitive  information  relating to the year
2000 will not have an Adverse Effect on Pierce Leahy.

         Section 3.8.  Related  Transactions.  Set forth in the Pierce Leahy SEC
Reports or on Section  3.8 of the Pierce  Leahy  Disclosure  Schedule is a true,
correct and complete (in all material  respects)  description of any Contractual
Obligation or  transaction,  whether now existing or existing  during the period
covered by the most recent audited Pierce Leahy  Financial  Statements,  between
Pierce Leahy or any Pierce Leahy  Subsidiary  and any  Affiliate  thereof or any
party  to the  Pierce  Leahy  Shareholders'  Agreement  that is  required  to be
disclosed pursuant to Item 404 of Regulation S-K, promulgated by the SEC.

         Section 3.9.      Tax Matters.

         (a) Each of  Pierce  Leahy  and each  Pierce  Leahy  Subsidiary  has in
accordance  with all Applicable Laws duly and timely filed all Tax Returns which
are  required to be filed,  and has paid,  or made  adequate  provision  for the
payment of, all Taxes shown on such Tax Returns which have or may become due and
payable  pursuant  to  said  Returns  and all  other  governmental  charges  and
assessments  received to date, other than any failure to file Tax Returns or pay
Taxes that would not,  individually or in the aggregate,  reasonably be expected
to have an Adverse Effect on Pierce Leahy. Except as would not,  individually or
in the  aggregate,  be reasonably  expected to have an Adverse  Effect on Pierce
Leahy, (i) the Tax Returns of Pierce Leahy and each Pierce Leahy Subsidiary have
been  prepared in accordance  with all  Applicable  Laws and generally  accepted
principles  applicable to taxation  consistently  applied;  (ii) all Taxes which
Pierce  Leahy and each Pierce Leahy  Subsidiary  are required by law to withhold
and collect have been duly withheld and collected, and have been paid over, in a
timely  manner,  to the proper  Authorities  to the extent due and payable;  and
(iii)  neither  Pierce  Leahy nor any Pierce Leahy  Subsidiary  has executed any
waiver to extend, or


<PAGE>


                                       11

otherwise  taken or failed to take any  action  that  would  have the  effect of
extending,  the  applicable  statute  of  limitations  in  respect  of  any  Tax
liabilities of Pierce Leahy or any Pierce Leahy  Subsidiary for the fiscal years
prior to and including the most recent fiscal year. Neither Pierce Leahy nor any
Pierce Leahy  Subsidiary  is a  "consenting  corporation"  within the meaning of
Section  341(f)  of the  Code.  Each of  Pierce  Leahy  and  each  Pierce  Leahy
Subsidiary has at all times been taxable as a Subchapter C corporation under the
Code,  except as  otherwise  set forth in  Section  3.9(a) of the  Pierce  Leahy
Disclosure  Schedule.  Neither Pierce Leahy nor any Pierce Leahy  Subsidiary has
ever been a member of any consolidated group (other than exclusively with Pierce
Leahy and its  Subsidiaries)  for Tax  purposes,  except as set forth in Section
3.9(a) of the Pierce Leahy Disclosure Schedule.

         (b)  From the end of its most  recent  fiscal  year to the date of this
Agreement,  neither  Pierce Leahy nor any Pierce Leahy  Subsidiary  has made any
payment on account of any Taxes except regular payments required in the ordinary
course of  business,  consistent  with prior  practice,  with respect to current
operations or property presently owned.

         (c) The information shown on the Federal and foreign income Tax Returns
of Pierce  Leahy and its  Subsidiaries  is true,  correct  and  complete  in all
material respects and fairly and accurately  reflects the information  purported
to be shown.  Federal  and state  income  Tax  Returns  of Pierce  Leahy and its
non-foreign  Subsidiaries  have been examined by the Internal Revenue Service or
applicable  state  Authority  through the  taxable  periods set forth in Section
3.9(c) of the Pierce Leahy Disclosure Schedule, and neither Pierce Leahy nor any
Pierce  Leahy  Subsidiary  has been  notified in writing  regarding  any pending
examination,  except as shown in Section  3.9(c) of the Pierce Leahy  Disclosure
Schedule.

         (d) Neither Pierce Leahy nor any Pierce Leahy  Subsidiary is a party to
any tax sharing agreement or arrangement.

         (e) Neither Pierce Leahy nor any Pierce Leahy  Subsidiary is, and since
the date of its  incorporation  has not been,  a "United  States  real  property
holding corporation" as defined in Section 897 of the Code.

         Section 3.10. ERISA.

         (a) Neither  Pierce  Leahy nor any Pierce Leahy  Subsidiary  (which for
purposes of this Section 3.10 shall include any ERISA  Affiliate with respect to
any Plan subject to Title IV of ERISA)  contributes  to any Plan or sponsors any
Plan or Benefit  Arrangement or, within the past five years,  has contributed to
or sponsored any Plan intended to comply with Section 401 of the Code, except as
set forth in Section 3.10(a) of the Pierce Leahy Disclosure Schedule.  As to all
Plans and Benefit  Arrangements  listed in Section  3.10(a) of the Pierce  Leahy
Disclosure  Schedule,  and except as disclosed  in such  Section  3.10(a) of the
Pierce Leahy Disclosure Schedule:

                  (i) all such  Plans  and  Benefit  Arrangements  substantially
         comply and have been  administered in all material respects in form and
         in operation with all Applicable Laws, all required returns  (including
         without  limitation  information  returns)  have been  prepared  in all
         material  respects in accordance with all Applicable Laws and have been
         timely  filed  with any  Authority  with  respect  to any such  Plan or
         Benefit Arrangement, and neither Pierce Leahy


<PAGE>


                                       12

         nor any Pierce Leahy  Subsidiary has received any  outstanding  written
         notice from any Authority questioning or challenging such compliance;

                  (ii) all such Plans  maintained  or  previously  maintained by
         Pierce Leahy or any Pierce Leahy  Subsidiary  that are or were intended
         to comply  with  Section  401 of the Code  comply and  complied  in all
         material  respects  in  form  and  in  operation  with  all  applicable
         requirements of such Section, a favorable determination letter has been
         received  from the Internal  Revenue  Service with respect to each such
         Plan or the  sponsor  of the Plan is  entitled  to rely on a  favorable
         opinion letter issued to the prototype  sponsor by the Internal Revenue
         Service  with  respect  to  each  such  Plan  or an  application  for a
         favorable  determination  letter is pending with the  Internal  Revenue
         Service,  and no event has occurred  which will or would  reasonably be
         expected to give rise to  disqualification  of any such Plan under such
         Section or to a tax under Section 511 of the Code;

                  (iii)  none of the  assets  of any such Plan are  invested  in
         employer securities or employer real property;

                  (iv)  neither  Pierce  Leahy nor any of its  Subsidiaries  has
         engaged in any  non-exempt  prohibited  transactions  (as  described in
         Section 406 of ERISA or Section  4975 of the Code) with  respect to any
         such Plan;

                  (v) there have been no acts or  omissions  by Pierce  Leahy or
         any  Pierce  Leahy  Subsidiary  which  have  given  rise  to  or  would
         reasonably be expected to give rise to material fines, penalties, taxes
         or related  charges under Sections  502(c),  502(i) or 4071 of ERISA or
         Chapter  43 of the Code for  which  Pierce  Leahy or any  Pierce  Leahy
         Subsidiary may be liable;

                  (vi) there are no material  Claims (other than routine  claims
         for benefits)  pending or, to Pierce Leahy's  knowledge,  threatened in
         writing involving such Plans or the assets of such Plans, except as set
         forth on Section 3.10(a)(vi) of the Pierce Leahy Disclosure Schedule;

                  (vii) no such  Plan is  subject  to Title IV of  ERISA,  or if
         subject,  there  have been no  "reportable  events"  (as  described  in
         Section  4043 of  ERISA)  as to  which  there is any  material  risk of
         termination of such Plan, and no steps have been taken to terminate any
         such Plan;

                  (viii) neither Pierce Leahy nor, to Pierce Leahy's  knowledge,
         any Pierce  Leahy  Subsidiary  nor any of their  respective  directors,
         officers,  employees or any other  fiduciary has committed any material
         breach of fiduciary  responsibility imposed by ERISA that would subject
         Pierce Leahy or any Pierce Leahy  Subsidiary or any of their respective
         directors, officers or employees to liability under ERISA;

                  (ix) no such Plan which is subject to Part 3 of  Subtitle B of
         Title I of ERISA or Section 412 of the Code had an accumulated  funding
         deficiency  (as  defined in Section 302 of ERISA and Section 412 of the
         Code),  whether or not waived,  as of the last day of the most recently
         completed fiscal year of such Plan;


<PAGE>
                                       13


                  (x) no material  liability to the PBGC has been or is expected
         by Pierce Leahy or any Pierce Leahy Subsidiary to be incurred by Pierce
         Leahy or any Pierce Leahy Subsidiary with respect to any such Plan, and
         there has been no event or condition  which presents a material risk of
         termination of any such Plan by the PBGC; and

                  (xi) except as set forth in Section  3.10(a)(xi) of the Pierce
         Leahy Disclosure  Schedule (which entry, if applicable,  shall indicate
         the present  value of  accumulated  plan  liabilities  calculated  in a
         manner  consistent  with FAS 106 and  actual  annual  expense  for such
         benefits  for  each of the  last  two (2)  years)  or  pursuant  to the
         provisions of COBRA,  which  provisions  have been complied with in all
         material respects, neither Pierce Leahy nor any Pierce Leahy Subsidiary
         maintains any Plan that provides benefits  described in Section 3(1) of
         ERISA to any former employees or retirees of Pierce Leahy or any of its
         Subsidiaries.

         (b)  Except  as  disclosed  in  Section  3.10(b)  of the  Pierce  Leahy
Disclosure Schedule,  neither Pierce Leahy nor any Pierce Leahy Subsidiary is or
ever has been a party to any  Multiemployer  Plan or made  contributions  to any
such plan.

         Section 3.11. Authorized and Outstanding Capital Stock.

         (a) As of September 30, 1999, the authorized  and  outstanding  capital
stock of Pierce  Leahy was as set forth in Section  3.11(a) of the Pierce  Leahy
Disclosure  Schedule.  All of such  outstanding  capital  stock  has  been  duly
authorized  and  validly  issued,  is fully  paid and  nonassessable  and is not
subject to any preemptive or similar rights. From September 30, 1999 through the
date of this Agreement,  Pierce Leahy has not issued any shares of capital stock
other  than  issuances  of Pierce  Leahy  Common  Stock in  accordance  with the
exercise  of  Pierce  Leahy  Options  or under  Pierce  Leahy's  401(k)  Plan in
accordance  with past  practice.  Shares of Pierce Leahy Common Stock issued and
outstanding on the record date for the Pierce Leahy Special  Meeting will be the
only class of capital stock eligible to vote on this  Agreement,  the Merger and
the Transactions. Except as set forth in Section 3.11(a) or 3.1(d) of the Pierce
Leahy Disclosure Schedule, (i) there is neither outstanding nor has Pierce Leahy
or any  Pierce  Leahy  Subsidiary  agreed  to grant or issue  any  shares of its
capital stock, other equity interests, any Option Security, Convertible Security
or Voting Debt, and (ii) neither Pierce Leahy nor any Pierce Leahy Subsidiary is
a party to and neither Pierce Leahy nor any Pierce Leahy  Subsidiary is bound by
any Contractual Obligation,  put or commitment pursuant to which it is obligated
to purchase,  redeem or  otherwise  acquire any shares of capital  stock,  other
equity  interests,  any Option  Security,  Convertible  Security or Voting Debt.
Neither Pierce Leahy nor any Pierce Leahy Subsidiary has any bonds,  debentures,
notes or other  Indebtedness  having general  voting rights or convertible  into
instruments  having general voting rights ("Voting Debt")  outstanding.  Between
the date of this  Agreement  and the  Closing,  except as set  forth in  Section
3.11(a) of the Pierce Leahy Disclosure Schedule, neither Pierce Leahy nor any of
its  Subsidiaries  will  issue,  sell or  purchase  or agree to  issue,  sell or
purchase  any  capital  stock,  other  equity  interests,  any Option  Security,
Convertible  Security or Voting Debt of Pierce Leahy or any of its Subsidiaries,
except to the extent required or permitted  pursuant to the terms hereof. All of
the issued  and  outstanding  shares of Pierce  Leahy's  capital  stock and each
Option Security or Convertible  Security of Pierce Leahy were issued and sold or
granted in compliance  with the Securities Act and applicable  state  securities
laws.



<PAGE>


                                       14

         (b) As of September 30, 1999, (i) Option  Securities to acquire 288,500
shares of Pierce Leahy Common Stock were  outstanding  under Pierce Leahy's 1997
Stock  Option Plan (the  "Pierce  Leahy 1997 Option  Plan"),  including  in such
number Option Securities which were then exercisable to acquire 29,003 shares of
Pierce Leahy Common Stock; (ii) Option Securities to acquire 1,047,746 shares of
Pierce Leahy Common Stock were  outstanding  under Pierce  Leahy's  Nonqualified
Stock Option Plan (the "Pierce  Leahy  Nonqualified  Option Plan" and,  together
with the 1997 Option Plan, the "Pierce Leahy Option  Plans"),  including in such
number Option  Securities  which were then exercisable to acquire 802,400 shares
of Pierce Leahy Common Stock;  and (iii) 1,211,000 shares of Pierce Leahy Common
Stock were reserved for future issuance  pursuant to Option Securities which may
be granted under the Pierce Leahy Option Plans.  From September 30, 1999 through
the date of this Agreement, neither Pierce Leahy nor any of its Subsidiaries has
issued any Option Securities.  The Pierce Leahy Option Plans constitute the only
plans  or  arrangements  pursuant  to which  Option  Securities  or  Convertible
Securities  to  acquire  shares of capital  stock of Pierce  Leahy or any of its
Subsidiaries  are  currently  outstanding.  Other  than as set forth in  Section
3.11(b) of the Pierce  Leahy  Disclosure  Schedule,  neither the  execution  and
delivery  of  this  Agreement  nor  the   consummation  of  the  Merger  or  the
Transactions  are events  which will cause an  acceleration  of the  exercise or
vesting schedule of any such Option Security or Convertible Security. All shares
of Pierce Leahy capital stock  subject to issuance  under an Option  Security or
Convertible  Security of Pierce Leahy or any of its  Subsidiaries  will be, upon
issuance  on the terms and  conditions  specified  in such  Option  Security  or
Convertible Security, validly issued, fully paid and nonassessable.

         (c) There are no voting  trusts or other  arrangements  to which Pierce
Leahy or any Pierce  Leahy  Subsidiary  is a party with respect to the voting of
capital  stock of Pierce  Leahy or any Pierce  Leahy  Subsidiary,  except as set
forth in Section 3.11(c) of the Pierce Leahy Disclosure Schedule.

         (d) At the  Effective  Time and at the time of issuance,  the shares of
Pierce Leahy Common Stock issued pursuant to the Merger will be duly authorized,
validly issued,  fully paid and  nonassessable and not subject to preemptive (or
similar)  rights.  All shares of Pierce Leahy  Common Stock  subject to issuance
pursuant to converted Iron Mountain  Options will be, upon issuance on the terms
and conditions specified in the applicable Iron Mountain Option, validly issued,
fully  paid and  nonassessable.  As a result  of an  election  duly and  validly
authorized,  Pierce Leahy is not subject to  Subchapter E (Sections  2541-2548),
Subchapter G (Sections  2561-2568) and Subchapter H (Sections  2571-2578) of the
PBCL.

         Section 3.12. Employment Arrangements.

         (a) Neither  Pierce  Leahy nor any Pierce  Leahy  Subsidiary  is now or
during  the past  three  (3) years  (at the time it was a  Subsidiary  of Pierce
Leahy)  has been  subject to or  involved  in or, to Pierce  Leahy's  knowledge,
threatened  in writing  with any union  elections,  petitions  therefor or other
organizational or recruiting activities,  except as described in Section 3.12(a)
of the Pierce Leahy Disclosure Schedule.  Except as set forth in Section 3.12(a)
of the Pierce Leahy Disclosure  Schedule,  none of the employees of Pierce Leahy
and its Subsidiaries are now, or during the past three (3) years (at the time it
was a Subsidiary of Pierce Leahy) have been,  represented  by any labor union or
other employee collective bargaining organization or are parties to any labor or
other  collective  bargaining  agreement,  and there are no pending  grievances,
disputes  or  controversies  with any  union or any  other  employee  collective
bargaining  organization  of such  employees,  or, to Pierce Leahy's  knowledge,
threats in writing of  strikes,  work  stoppages  or  slowdowns  or any  pending
demands for


<PAGE>


                                       15

collective  bargaining by any union or other such  organization  or by any other
employees, except as would not, individually or in the aggregate,  reasonably be
expected to have an Adverse Effect on Pierce Leahy.

         (b)  Except  as set  forth  in  Section  3.12(b)  of the  Pierce  Leahy
Disclosure Schedule,  no employee of Pierce Leahy or any Pierce Leahy Subsidiary
will accrue or receive or is entitled to accrue or receive additional  benefits,
service or  accelerated  rights to payments of benefits,  including the right to
receive any parachute payment, as defined in Section 280G of the Code, or become
entitled to severance,  termination allowance or similar payments as a result of
this Agreement, the Merger or the Transactions.

         Section 3.13. Material Agreements. To Pierce Leahy's knowledge,  listed
on  Section  3.13 of the  Pierce  Leahy  Disclosure  Schedule  are all  Material
Agreements to which Pierce Leahy or any Pierce Leahy Subsidiary is a party or to
which it or any of its property is subject or bound. True,  complete and correct
copies of each of the Material Agreements have been furnished by Pierce Leahy to
Iron Mountain.  All of the Material  Agreements  are valid,  binding and legally
enforceable  obligations of Pierce Leahy and, to Pierce Leahy's  knowledge,  the
other parties thereto (subject to the Enforceability  Exceptions),  except where
the  lack  of  enforceability  would  not,  individually  or in  the  aggregate,
reasonably be expected to have an Adverse Effect on Pierce Leahy.  Except as set
forth in Section 3.13 of the Pierce Leahy Disclosure Schedule,  Pierce Leahy and
each Pierce Leahy  Subsidiary  have duly complied in all material  respects with
all of the terms and conditions of each Material  Agreement and have not done or
performed,  or failed  to do or  perform  (and  there is no  pending  or, to the
knowledge of Pierce Leahy,  threatened  (in writing)  Claim that Pierce Leahy or
any Pierce Leahy Subsidiary has not so complied, done and performed or failed to
do and  perform) any act the effect of which would be to  invalidate  or provide
grounds  for the other  party  thereto to  terminate  (with or  without  notice,
passage  of time or both)  such  Material  Agreement  or  impair  the  rights or
benefits, or increase the costs, of Pierce Leahy or any Pierce Leahy Subsidiary,
under any of the Material Agreements, except as would not reasonably be expected
to have,  individually  or in the aggregate,  an Adverse Effect on Pierce Leahy.
Except as set forth in Section  3.13 of the Pierce  Leahy  Disclosure  Schedule,
neither the execution and delivery of this Agreement or any Collateral  Document
executed  or  required  to be  executed  pursuant  hereto  or  thereto,  nor the
consummation of the Transactions,  nor compliance with the terms, conditions and
provisions  hereof or thereof by Pierce Leahy will conflict with, or result in a
breach  or  violation  of,  or  constitute  a  default  under,   or  permit  the
acceleration  of any  obligation or liability in, or but for any  requirement of
giving of notice or  passage of time or both  would  constitute  such a conflict
with,  breach or violation of, or default under, or permit any such acceleration
in, any Material Agreement.

         Section  3.14.  Ordinary  Course  of  Business.  Except as set forth in
Section 3.14 of the Pierce Leahy Disclosure  Schedule or disclosed in the Pierce
Leahy  SEC  Reports,  since the date of the most  recent  audited  Pierce  Leahy
Financial  Statements  included in the Pierce Leahy SEC Reports through the date
of this  Agreement,  Pierce  Leahy  and its  Subsidiaries  have  operated  their
respective businesses only in the ordinary and usual course and in substantially
the same manner as previously conducted and there has not been:



<PAGE>


                                       16

                  (i) any  damage,  destruction  or  loss  with  respect  to the
         properties  or  assets  of  Pierce  Leahy or its  Subsidiaries  whether
         covered  by  insurance  or not,  which has had or would  reasonably  be
         expected to have,  individually or in the aggregate,  an Adverse Effect
         with respect to Pierce Leahy;

                  (ii) any other change,  occurrence or circumstance that had or
         would  reasonably be expected to have an Adverse Effect with respect to
         Pierce Leahy;

                  (iii) any  change  to any  accounting  methods  used by Pierce
         Leahy, unless required in accordance with GAAP;

                  (iv)  any  declaration  or  payment  of any  Distributions  in
         respect of the  outstanding  shares of capital stock of Pierce Leahy or
         any of its  Subsidiaries  (other  than  dividends  declared  or paid by
         wholly-owned   Subsidiaries  or   Distributions  on  the  Pierce  Leahy
         Preferred Stock in accordance with its terms);

                  (v) any  split,  combination  or  reclassification  of  Pierce
         Leahy's  capital  stock or any  issuance of shares of capital  stock of
         Pierce Leahy or any Pierce Leahy  Subsidiary or any other change in the
         authorized   capitalization   of  Pierce  Leahy  or  any  Pierce  Leahy
         Subsidiary,  except as  contemplated  or permitted by this Agreement or
         pursuant  to  employee  benefit  plans,  programs  or  arrangements  in
         existence on the date of this Agreement;

                  (vi) any repurchase or redemption by Pierce Leahy of shares of
         its  capital  stock  or any  issuance  by  Pierce  Leahy  of any  other
         securities  in  exchange or in  substitution  for shares of its capital
         stock  except   pursuant  to  employee   benefit  plans,   programs  or
         arrangements  in  existence  on the  date  of  this  Agreement,  in the
         ordinary course of business consistent with past practice;

                  (vii)  any  grant  or  award  of  any  Option   Securities  or
         Convertible Securities or other rights to acquire any shares of capital
         stock or other  equity  interests  of Pierce  Leahy or any  Subsidiary,
         except  as  contemplated  or  permitted  by this  Agreement  or  except
         pursuant  to  employee  benefit  plans,  programs  or  arrangements  in
         existence  on the date of this  Agreement,  in the  ordinary  course of
         business consistent with past practice; or

                  (viii) any sale or other  disposal of, or any contract to sell
         or otherwise dispose of, any of its properties or assets, other than in
         the ordinary course of business.

         Section 3.15. Broker or Finder.  Except as set forth on Section 3.15 of
the Pierce Leahy Disclosure Schedule, no Person assisted in or brought about the
negotiation  of  this  Agreement,  the  Merger  or  the  subject  matter  of the
Transactions  in the  capacity  of  broker,  agent or finder  or in any  similar
capacity on behalf of Pierce Leahy or is entitled to any brokerage,  finder's or
other fee or commission from Pierce Leahy in connection  with the  Transactions.
Pierce Leahy has  heretofore  furnished to Iron  Mountain a complete and correct
copy of all agreements between Pierce Leahy and the Persons set forth on Section
3.15 of the Pierce Leahy Disclosure Schedule pursuant to which such Person would
be entitled to payment relating to the Transactions.



<PAGE>


                                       17

         Section 3.16. Environmental Matters.

         (a)  Except  as set  forth  in  Section  3.16(a)  of the  Pierce  Leahy
Disclosure  Schedule,  Pierce Leahy and its Subsidiaries  have complied with all
applicable  Environmental  Laws except  where the failure to comply would not be
reasonably  expected  to have an  Adverse  Effect on Pierce  Leahy.  There is no
pending or, to Pierce  Leahy's  knowledge,  threatened  (in  writing),  civil or
criminal  Legal  Actions,  written  notice of violation,  formal  administrative
proceeding or  investigation,  inquiry or  information  request by any Authority
relating  to  any  Environmental  Law  involving  Pierce  Leahy  or  any  of its
Subsidiaries  or any of their  properties,  which would,  individually or in the
aggregate, not reasonably be expected to have an Adverse Effect on Pierce Leahy.

         (b)  Except  as set  forth  in  Section  3.16(b)  of the  Pierce  Leahy
Disclosure Schedule, there have been no releases of any Hazardous Materials into
the  environment  by  Pierce  Leahy or any of its  Subsidiaries,  or,  to Pierce
Leahy's  knowledge,  by any other  party at any parcel of real  property  or any
facility formerly or currently owned,  operated or controlled by Pierce Leahy or
any of its  Subsidiaries  which would  reasonably be expected to have an Adverse
Effect on Pierce Leahy.

         (c) Section 3.16(c) of the Pierce Leahy  Disclosure  Schedule (which in
accordance with Section 5.16 hereof,  will be delivered  within thirty (30) days
after the date of this  Agreement)  sets forth all site  assessments,  audits or
other investigations that have been conducted by or on behalf of Pierce Leahy or
any Pierce Leahy Subsidiary  within the last three (3) years as to environmental
matters at any property owned,  leased,  operated or occupied by Pierce Leahy or
any Pierce Leahy Subsidiary.

         Section 3.17. Board Action; Fairness Opinion.

         (a) The Board of Directors of Pierce Leahy at a meeting duly called and
held, has by unanimous vote of those directors  present (who constituted 100% of
the  directors  then in  office)  (i)  determined  that this  Agreement  and the
Transactions,  including  the Merger,  are in the best  interests  of the Pierce
Leahy  Shareholders  and has approved the same,  (ii) resolved to recommend that
the holders of the shares of Pierce Leahy Common Stock adopt this  Agreement and
the  Transactions,  including the Merger and (iii) nominated and recommended for
election to the Pierce  Leahy  Stockholders  the  individuals  who will serve as
members of the Board of Directors of the Surviving  Corporation at the Effective
Time.

         (b) Pierce Leahy has  received  the opinion of First Union  Securities,
Inc.,  dated as of October 20, 1999, to the effect that, as of the date thereof,
the  consideration  to be received in the Merger by the  shareholders  of Pierce
Leahy is fair, from a financial point of view, to such  shareholders.  A signed,
true and complete  copy of such opinion has been  delivered to Iron  Mountain or
will be promptly delivered to Iron Mountain by Pierce Leahy.

         Section  3.18.  Materiality.  The matters and items  excluded  from the
representations  and  warranties  set forth in this  Article by operation of the
materiality  exceptions  and  materiality   qualifications   contained  in  such
representations  and warranties,  in the aggregate for all such excluded matters
and items,  are not and would not reasonably be expected to be Adverse to Pierce
Leahy.



<PAGE>
                                       18

                                   ARTICLE 4.

                 REPRESENTATIONS AND WARRANTIES OF IRON MOUNTAIN

         Iron  Mountain  hereby  represents  and  warrants  to  Pierce  Leahy as
follows:

         Section 4.1. Organization and Business; Power and Authority;  Effect of
Transaction.

         (a)      Iron Mountain:

                  (i) is a corporation  duly organized,  validly existing and in
         good standing under the laws of the State of Delaware,

                  (ii) has all requisite corporate power and corporate authority
         to own or hold under lease its  properties and to conduct its business,
         and has in full force and effect all  Governmental  Authorizations  and
         Private  Authorizations and has made all Governmental  Filings,  to the
         extent  required  for such  ownership  and  lease of its  property  and
         conduct of its business, except to the extent the failure to be in full
         force and effect or to have made such  Governmental  Filings would not,
         individually  or in the  aggregate,  reasonably  be expected to have an
         Adverse Effect, and

                  (iii) is duly  qualified and  authorized to do business and is
         in good standing as a foreign corporation in each jurisdiction in which
         the  character  of its  property  or the  nature  of  its  business  or
         operations requires such qualification or authorization,  except to the
         extent the  failure to so qualify or to  maintain  such  authorizations
         would not reasonably be expected to have an Adverse Effect.

         (b) Iron  Mountain  has all  requisite  corporate  power and  corporate
authority to execute and deliver,  and to perform its  obligations  under,  this
Agreement and each Collateral Document executed or required to be executed by it
pursuant  hereto or thereto and to consummate  the Merger and the  Transactions,
and  the  execution,  delivery  and  performance  of  this  Agreement  and  each
Collateral Document executed or required to be executed by it pursuant hereto or
thereto have been duly authorized by all requisite  corporate action (other than
that of the Iron Mountain  Stockholders).  This Agreement has been duly executed
and delivered by Iron Mountain and  constitutes,  and each  Collateral  Document
executed or  required  to be  executed  by it  pursuant  hereto or thereto or to
consummate the Merger and the Transactions,  when executed and delivered by Iron
Mountain or an Iron  Mountain  Stockholder  will  constitute,  legal,  valid and
binding  obligations  of  Iron  Mountain  or  such  Iron  Mountain  Stockholder,
enforceable  in  accordance  with  their  respective   terms,   except  as  such
enforceability may be subject to the Enforceability  Exceptions. The affirmative
vote of the holders of a majority  of the  outstanding  shares of Iron  Mountain
Common  Stock is the only  vote of the  holders  of any  class or  series of the
capital stock of Iron Mountain  necessary to approve this Agreement,  the Merger
and the Transactions under Applicable Law and Iron Mountain's Organic Documents.
The provisions of Section 203 of the DGCL will not apply to this Agreement,  the
Merger or the Transactions.

         (c)  Except  as set  forth  in  Section  4.1(c)  of the  Iron  Mountain
Disclosure  Schedule  (which in accordance  with Section 5.16 hereof (other than
those sections relating to Applicable Law,


<PAGE>


                                       19

Organic  Documents and Material  Agreements,  which  sections shall be delivered
herewith),  will be  delivered  within  thirty  (30) days after the date of this
Agreement),  neither  the  execution  and  delivery  of  this  Agreement  or any
Collateral  Document  executed or required  to be  executed  pursuant  hereto or
thereto,  nor the  consummation  of the  Transactions,  nor compliance  with the
terms, conditions and provisions hereof or thereof by Iron Mountain:

                  (i) will conflict with, or result in a breach or violation of,
         or constitute a default  under,  any Applicable Law on the part of Iron
         Mountain or any Iron  Mountain  Subsidiary  or will  conflict  with, or
         result in a breach or violation of, or constitute a default  under,  or
         permit the  acceleration  of any obligation or liability in, or but for
         any  requirement  of giving of notice or  passage of time or both would
         constitute  such a conflict  with,  breach or violation  of, or default
         under, or permit any such  acceleration in, any Organic Document or any
         Contractual   Obligation   of  Iron   Mountain  or  any  Iron  Mountain
         Subsidiary,  other than any such conflict, breach, violation or default
         as would not, individually or in the aggregate,  reasonably be expected
         to have an Adverse Effect,

                  (ii) will result in or permit the  creation or  imposition  of
         any Lien upon any property now owned or leased by Iron  Mountain or any
         Iron Mountain Subsidiary,  except for such Liens that,  individually or
         in the  aggregate,  would not reasonably be expected to have an Adverse
         Effect,

                  (iii)  will   require  any   Governmental   Authorization   or
         Governmental   Filing  or   Private   Authorization,   except  for  the
         certificate  and articles of merger and related  filings under the DGCL
         and the PBCL in  connection  with the Merger and the  Transactions  and
         except  pursuant to the HSR Act, the Exchange Act , the  Securities Act
         or any  applicable  state  securities  laws, or as otherwise  would not
         reasonably be expected to have an Adverse Effect.

         (d) Iron Mountain does not have any  Subsidiaries  other than those set
forth on Section 4.1(d) of the Iron Mountain Disclosure Schedule,  each of which
is directly or indirectly wholly owned (except as set forth in Section 4.1(d) of
the Iron Mountain  Disclosure  Schedule),  is an Entity which is duly organized,
validly  existing  and in  good  standing  under  the  laws  of  the  respective
jurisdiction  of  organization  set forth opposite its name on Section 4.1(d) of
the  Iron  Mountain  Disclosure  Schedule,  and is  duly  qualified  and in good
standing in each other  jurisdiction  in which the  character of its property or
the  nature  of its  business  or  operations  requires  such  qualification  or
authorization  (except to the extent the failure to be duly  organized,  validly
existing or in good standing or to so qualify would not,  individually or in the
aggregate,  reasonably  be  expected  to  have an  Adverse  Effect),  with  full
corporate or similar  power and  corporate or similar  authority to carry on the
business  in which it is engaged.  Except as set forth in Section  4.1(d) to the
Iron Mountain  Disclosure  Schedule,  each Iron Mountain  Subsidiary has in full
force and effect all Governmental Authorizations and Private Authorizations, and
has made all Governmental  Filings to the extent required for such ownership and
lease of its  property  and  conduct of its  business,  except to the extent the
failure to so have such  Authorizations or made such Governmental  Filings would
not, individually or in the aggregate, reasonably be expected to have an Adverse
Effect.  Except to the extent set forth on Section  4.1(d) of the Iron  Mountain
Disclosure  Schedule,  Iron Mountain owns,  directly or indirectly through other
Iron Mountain Subsidiaries, all of the outstanding capital stock or other equity
interests (as shown on Section 4.1(d) of the Iron Mountain Disclosure  Schedule)
of each Iron  Mountain  Subsidiary,  free and clear of all  Liens,  and all such
stock or other equity interests


<PAGE>


                                       20

have  been  duly   authorized   and  validly  issued  and  are  fully  paid  and
nonassessable  and were issued and sold in compliance  with the Securities  Act,
the Exchange Act and applicable state  securities  laws.  Except as set forth in
Section 4.1(d) of the Iron Mountain  Disclosure  Schedule,  (i) there is neither
outstanding  nor has any Iron Mountain  Subsidiary  agreed to grant or issue any
shares of its capital stock or other equity  interests or any Option Security or
Convertible  Security,  and (ii) no Iron Mountain Subsidiary is a party to or is
bound by any agreement,  put or commitment  pursuant to which it is obligated to
purchase,  redeem or  otherwise  acquire  any shares of  capital  stock or other
equity interests or any Option Security or Convertible Security.

         (e) Iron  Mountain  does not own any  capital  stock or equity or other
interest in any other Entity or enterprise,  however  organized and however such
interest may be denominated or evidenced,  except as set forth in Section 4.1(d)
or 4.1(e) of the Iron Mountain Disclosure Schedule.

         Section 4.2. SEC Filings; Financial Statements.

         (a) Iron Mountain has filed all forms,  reports and documents  required
to be filed by it with the SEC,  and has  heretofore  made  available  to Pierce
Leahy, in the form filed with the SEC (including any exhibits thereto),  (i) its
Annual Report on Form 10-K for the fiscal year ended December 31, 1998, (ii) its
Quarterly  Reports on Form 10-Q for the  quarters  ended March 31, 1999 and June
30,  1999,   (iii)  its  proxy  statement   relating  to  its  1999  meeting  of
stockholders,  (iv) all of its registration  statements that are effective as of
the date of this Agreement  under which shares of Iron Mountain Common Stock are
still  available  for issuance (a complete list of which is set forth in Section
4.2(a) of the Iron  Mountain  Disclosure  Schedule),  and (v) all  other  forms,
reports and  registration  statements  filed by it with the SEC since January 1,
1999 (the forms, reports and other documents referred to in clauses (i), through
(v) above,  together with all other forms,  reports and documents  filed by Iron
Mountain  with the SEC,  being  referred  to  herein  collectively  as the "Iron
Mountain SEC Reports"). The Iron Mountain SEC Reports and any forms, reports and
other  documents  filed by Iron  Mountain  with the SEC  after  the date of this
Agreement,  (x) complied  with or will comply in all material  respects with the
requirements of the Securities Act and the Exchange Act, as the case may be, and
the  rules  and  regulations  thereunder  and (y) did not at the time  they were
filed, or will not at the time they are filed, contain any untrue statement of a
material fact or omit to state a material fact required to be stated  therein or
necessary  in order to make the  statements  made  therein,  in the light of the
circumstances  under  which they were made,  not  misleading;  provided  that no
representation  or warranty is made with respect to any information  provided by
Pierce Leahy that is or will be included in any Iron  Mountain SEC Report.  None
of Iron Mountain's  Subsidiaries is required to file any forms, reports or other
documents with the SEC pursuant to Section 12 or 15 of the Exchange Act.

         (b) Iron Mountain's  financial  statements,  including in each case the
notes  thereto,  contained in its Annual Report on Form 10-K for the fiscal year
ended December 31, 1998 and its Quarterly  Reports on Form 10-Q for the quarters
ended  March  31,  1999  and  June  30,  1999  (the  "Iron  Mountain   Financial
Statements")  (i) have been prepared from, and are in accordance with, the books
and records of Iron Mountain and its consolidated  Subsidiaries,  (ii) comply in
all material respects with applicable accounting requirements and with published
rules and regulations of the SEC with respect thereto,  (iii) have been prepared
in accordance  with GAAP applied on a consistent  basis  throughout  the periods
covered  thereby,  except as  otherwise  noted  therein,  are true,  correct and
complete,  and (iv)  fairly  present  the  financial  condition  and  results of
operations and cash flows of

<PAGE>
                                       21

Iron  Mountain and its  Subsidiaries,  on the bases  therein  stated,  as of the
respective  dates  thereof,  and  for the  respective  periods  covered  thereby
subject,  in the case of unaudited  financial  statements to normal  nonmaterial
year-end  audit  adjustments  and  accruals  and  to  the  absence  of  complete
footnotes.

         Section 4.3.  Changes in  Condition.  Since the date of the most recent
financial  statements  forming part of the Iron Mountain  Financial  Statements,
except to the extent specifically  described in Section 4.3 of the Iron Mountain
Disclosure Schedule,  there has been no Adverse Change in Iron Mountain. To Iron
Mountain's  knowledge,  there is no Event known to Iron Mountain which Adversely
Affects,  or would reasonably be expected to Adversely Affect, Iron Mountain and
its  Subsidiaries,  taken as a whole, or the ability of Iron Mountain to perform
any of the  obligations  set forth in this Agreement or any Collateral  Document
executed or required to be executed pursuant hereto or thereto.

         Section 4.4.  Liabilities.  (i) At the date of the most recent  balance
sheet  forming  part of the Iron  Mountain  Financial  Statements,  neither Iron
Mountain nor any Iron Mountain  Subsidiary had any  obligations or  liabilities,
accrued or unaccrued, fixed, absolute,  contingent or other (including,  without
limitation,  any contingent  payments or "earnouts"  owing under any acquisition
agreement), except as disclosed in such balance sheet, or the notes thereto, and
(ii) since such date, neither Iron Mountain nor any Iron Mountain Subsidiary has
incurred any such  obligations or liabilities,  other than those incurred in the
ordinary  course of business  consistent with past practice of Iron Mountain and
Iron Mountain Subsidiaries,  and other than obligations and liabilities which in
the case of clauses (i) and (ii) do not and, to Iron Mountain's knowledge, would
not,  individually  or in the  aggregate,  reasonably  be expected to  Adversely
Affect Iron Mountain,  except to the extent set forth in Section 4.4 of the Iron
Mountain  Disclosure  Schedule.  Neither  Iron  Mountain  nor any Iron  Mountain
Subsidiary  has guaranteed or is otherwise  primarily or  secondarily  liable in
respect of any  obligation  or liability  of any other  Person  (other than Iron
Mountain or an Iron Mountain Subsidiary),  except for endorsements of negotiable
instruments  for deposit in the  ordinary  course of business,  consistent  with
prior  practice,  or as disclosed in the most recent balance sheet, or the notes
thereto,  forming part of the Iron Mountain  Financial  Statements or in Section
4.4 of the Iron Mountain Disclosure Schedule.

         Section  4.5.  Title  to  Properties;   Leases.  Except  as  would  not
reasonably be expected to have an Adverse Effect on Iron Mountain,  each of Iron
Mountain and its  Subsidiaries  has good legal,  marketable and insurable title,
with respect to all real property owned (in fee simple), good title with respect
to all real  property  leased (in  leasehold)  reflected as an asset on the most
recent balance sheet forming part of the Iron Mountain Financial Statements,  or
held by Iron Mountain or any such Subsidiary for use in its business,  if not so
reflected,  and good  indefeasible and  merchantable  title to all other assets,
tangible and intangible, reflected on the most recent balance sheet forming part
of the Iron Mountain  Financial  Statements,  or (excluding  leased real estate)
held by Iron Mountain or any Iron Mountain Subsidiary for use in its business if
not so  reflected,  or purported to have been  acquired by Iron  Mountain or any
Iron Mountain Subsidiary since such date, except inventory sold or depleted,  or
property, plant and other equipment used up or retired, since such date, in each
case in the ordinary  course of business  consistent  with the past  practice of
Iron  Mountain  and its  Subsidiaries,  free and clear of all Liens,  except (i)
Liens reflected in the Iron Mountain Financial Statements,  (ii) Liens set forth
on Section  4.5(a) of the Iron Mountain  Disclosure  Schedule,  (iii)  Permitted
Liens,  and (iv) such  Liens that do not or would  not,  individually  or in the
aggregate,  reasonably be expected to have an Adverse  Effect on Iron  Mountain.
Each Lease or other occupancy


<PAGE>
                                       22

or other  agreement  under which Iron Mountain or any Iron  Mountain  Subsidiary
holds real or personal property has been duly authorized, executed and delivered
by Iron  Mountain  or an  Iron  Mountain  Subsidiary,  and,  to Iron  Mountain's
knowledge,  by each of the other  parties  thereto;  each such Lease is a legal,
valid and binding  obligation of Iron  Mountain or an Iron Mountain  Subsidiary,
and, to Iron Mountain's knowledge,  of each other party thereto,  enforceable in
accordance  with its terms (subject to the  Enforceability  Exceptions),  except
where the lack of such  authorization,  execution or delivery or the lack of the
legal,  valid and binding  nature of such  obligation  would not  reasonably  be
expected to have an Adverse Effect on Iron Mountain.

         Section 4.6. Compliance with Governmental Authorizations and Applicable
Law.

         (a) Section 4.6(a) of the Iron Mountain  Disclosure Schedule contains a
description of all Legal Actions which are pending in which Iron Mountain or any
Iron Mountain  Subsidiary is a party, or to which the businesses,  operations or
properties of Iron Mountain or any Iron Mountain  Subsidiary  are subject or, to
Iron  Mountain's  knowledge,  which are  threatened  in  writing  against,  Iron
Mountain or any Iron Mountain Subsidiary or any of their respective  businesses,
operations or properties, which, individually or in the aggregate, if determined
against  Iron  Mountain or any Iron  Mountain  Subsidiary  would  reasonably  be
expected to have an Adverse Effect on Iron Mountain.

         (b) Iron Mountain and its  Subsidiaries  have obtained all Governmental
Authorizations  which are necessary for the ownership or use of their respective
properties  and the conduct of their  respective  businesses as now conducted by
Iron  Mountain  or  any  Iron   Mountain   Subsidiary   and  such   Governmental
Authorizations  are in full  force  and  effect,  except  for such  Governmental
Authorizations  which,  if not obtained and maintained in full force and effect,
would  singly or in the  aggregate,  reasonably  be  expected to have an Adverse
Effect on Iron Mountain.  Neither Iron Mountain nor any Iron Mountain Subsidiary
is in  material  breach or  violation  of,  or in  default  in the  performance,
observance or fulfillment of, any  Governmental  Authorization or any Applicable
Law,  and no Event exists or has  occurred,  which  constitutes,  or but for any
requirement  of giving of notice or passage  of time or both  would  constitute,
such a breach, violation or default, under any Governmental Authorization or any
Applicable Law, except for such breaches,  violations or defaults as do not and,
to Iron  Mountain's  knowledge,  would not,  individually  or in the  aggregate,
reasonably be expected to have an Adverse Effect on Iron Mountain.

         Section  4.7.  Year 2000.  Any  inability  of Iron  Mountain's  and its
Subsidiaries' systems (including,  without limitation, any Year 2000 Systems) to
properly recognize and process date sensitive  information  relating to the year
2000 will not have an Adverse Effect on Iron Mountain.

         Section 4.8. Related  Transactions.  Set forth in the Iron Mountain SEC
Reports or on Section 4.8 of the Iron  Mountain  Disclosure  Schedule is a true,
correct and complete (in all material  respects)  description of any Contractual
Obligation or  transaction,  whether now existing or existing  during the period
covered by the most recent audited Iron Mountain Financial  Statements,  between
Iron Mountain or any Iron Mountain  Subsidiary and any Affiliate thereof that is
required to be disclosed pursuant to Item 404 of Regulation S-K,  promulgated by
the SEC.


<PAGE>

                                       23

         Section 4.9.      Tax Matters.

         (a) Each of Iron  Mountain  and each Iron  Mountain  Subsidiary  has in
accordance  with all Applicable Laws duly and timely filed all Tax Returns which
are  required to be filed,  and has paid,  or made  adequate  provision  for the
payment of, all Taxes shown on such Tax Returns which have or may become due and
payable  pursuant  to  said  Returns  and all  other  governmental  charges  and
assessments  received to date, other than any failure to file Tax Returns or pay
Taxes that would not,  individually or in the aggregate,  reasonably be expected
to have an Adverse Effect on Iron Mountain. Except as would not, individually or
in the  aggregate,  be  reasonably  expected  to have an Adverse  Effect on Iron
Mountain, (i) the Tax Returns of Iron Mountain and each Iron Mountain Subsidiary
have been prepared in accordance with all Applicable Laws and generally accepted
principles  applicable to taxation  consistently  applied;  (ii) all Taxes which
Iron Mountain and each Iron Mountain  Subsidiary are required by law to withhold
and collect have been duly withheld and collected, and have been paid over, in a
timely  manner,  to the proper  Authorities  to the extent due and payable;  and
(iii) neither Iron Mountain nor any Iron  Mountain  Subsidiary  has executed any
waiver to extend,  or  otherwise  taken or failed to take any action  that would
have the effect of extending,  the applicable  statute of limitations in respect
of any Tax liabilities of Iron Mountain or any Iron Mountain  Subsidiary for the
fiscal years prior to and including  the most recent  fiscal year.  Neither Iron
Mountain nor any Iron Mountain  Subsidiary is a "consenting  corporation" within
the meaning of Section  341(f) of the Code.  Each of Iron Mountain and each Iron
Mountain  Subsidiary has at all times been taxable as a Subchapter C corporation
under the Code,  except as  otherwise  set forth in  Section  4.9(a) of the Iron
Mountain  Disclosure  Schedule.  Neither  Iron  Mountain  nor any Iron  Mountain
Subsidiary  has  ever  been a  member  of any  consolidated  group  (other  than
exclusively with Iron Mountain and its Subsidiaries) for Tax purposes, except as
set forth in Section 4.9(a) of the Iron Mountain Disclosure Schedule.

         (b)  From the end of its most  recent  fiscal  year to the date of this
Agreement,  neither Iron Mountain nor any Iron Mountain  Subsidiary has made any
payment on account of any Taxes except regular payments required in the ordinary
course of  business,  consistent  with prior  practice,  with respect to current
operations or property presently owned.

         (c) The information shown on the Federal and foreign income Tax Returns
of Iron  Mountain  and its  Subsidiaries  is true,  correct and  complete in all
material respects and fairly and accurately  reflects the information  purported
to be shown.  Federal  and state  income Tax  Returns of Iron  Mountain  and its
non-foreign  Subsidiaries  have been examined by the Internal Revenue Service or
applicable  state  Authority  through the  taxable  periods set forth in Section
4.9(c) of the Iron Mountain Disclosure  Schedule,  and neither Iron Mountain nor
any Iron Mountain  Subsidiary has been notified in writing regarding any pending
examination,  except as shown in Section 4.9(c) of the Iron Mountain  Disclosure
Schedule.

         (d) Neither Iron Mountain nor any Iron  Mountain  Subsidiary is a party
to any tax sharing agreement or arrangement.

         (e) Neither Iron  Mountain  nor any Iron  Mountain  Subsidiary  is, and
since the date of its incorporation has not been, a "United States real property
holding corporation" as defined in Section 897 of the Code.

<PAGE>
                                       24

         Section 4.10. ERISA.

         (a) Neither Iron Mountain nor any Iron Mountain  Subsidiary  (which for
purposes of this Section 4.10 shall include any ERISA  Affiliate with respect to
any Plan subject to Title IV of ERISA)  contributes  to any Plan or sponsors any
Plan or Benefit  Arrangement or, within the past five years,  has contributed to
or sponsored any Plan intended to comply with Section 401 of the Code, except as
set forth in Section 4.10(a) of the Iron Mountain Disclosure Schedule. As to all
Plans and Benefit  Arrangements  listed in Section  4.10(a) of the Iron Mountain
Disclosure Schedule, and except as disclosed in such Section 4.10(a) of the Iron
Mountain Disclosure Schedule:

                  (i) all such  Plans  and  Benefit  Arrangements  substantially
         comply and have been  administered in all material respects in form and
         in operation with all Applicable Laws, all required returns  (including
         without  limitation  information  returns)  have been  prepared  in all
         material  respects in accordance with all Applicable Laws and have been
         timely  filed  with any  Authority  with  respect  to any such  Plan or
         Benefit  Arrangement,  and neither Iron  Mountain nor any Iron Mountain
         Subsidiary  has  received  any  outstanding  written  notice  from  any
         Authority questioning or challenging such compliance;

                  (ii) except as  described in Section  4.10(a)(ii)  of the Iron
         Mountain Disclosure  Schedule,  all such Plans maintained or previously
         maintained by Iron Mountain or any Iron Mountain Subsidiary that are or
         were  intended  to  comply  with  Section  401 of the Code  comply  and
         complied in all  material  respects in form and in  operation  with all
         applicable  requirements  of such  Section,  a favorable  determination
         letter has been received from the Internal Revenue Service with respect
         to each such Plan or the  sponsor of the Plan is  entitled to rely on a
         favorable  opinion  letter  issued  to  the  prototype  sponsor  by the
         Internal  Revenue  Service  with  respect  to  each  such  Plan  or  an
         application  for a favorable  determination  letter is pending with the
         Internal Revenue Service, and no event has occurred which will or would
         reasonably  be  expected to give rise to  disqualification  of any such
         Plan under such Section or to a tax under Section 511 of the Code;

                  (iii)  none of the  assets  of any such Plan are  invested  in
         employer securities or employer real property;

                  (iv) neither Iron  Mountain  nor any of its  Subsidiaries  has
         engaged in any  non-exempt  prohibited  transactions  (as  described in
         Section 406 of ERISA or Section  4975 of the Code) with  respect to any
         such Plan;

                  (v) there have been no acts or omissions  by Iron  Mountain or
         any  Iron  Mountain  Subsidiary  which  have  given  rise  to or  would
         reasonably be expected to give rise to material fines, penalties, taxes
         or related  charges under Sections  502(c),  502(i) or 4071 of ERISA or
         Chapter 43 of the Code for which  Iron  Mountain  or any Iron  Mountain
         Subsidiary may be liable;

                  (vi) there are no material  Claims (other than routine  claims
         for benefits) pending or, to Iron Mountain's  knowledge,  threatened in
         writing involving such Plans or the assets of such Plans, except as set
         forth on Section 4.10(a)(vi) of the Iron Mountain Disclosure Schedule;


<PAGE>
                                       25


                  (vii) except as described in Section  4.10(a)(vii) of the Iron
         Mountain  Disclosure  Schedule,  no such Plan is subject to Title IV of
         ERISA,  or if  subject,  there  have been no  "reportable  events"  (as
         described  in Section  4043 of ERISA) as to which there is any material
         risk of  termination  of such  Plan,  and no steps  have been  taken to
         terminate any such Plan;

                  (viii)   neither  Iron  Mountain   nor,  to  Iron   Mountain's
         knowledge,  any Iron Mountain  Subsidiary  nor any of their  respective
         directors, officers, employees or any other fiduciary has committed any
         material breach of fiduciary responsibility imposed by ERISA that would
         subject Iron Mountain or any Iron  Mountain  Subsidiary or any of their
         respective directors, officers or employees to liability under ERISA;

                  (ix) no such Plan which is subject to Part 3 of  Subtitle B of
         Title I of ERISA or Section 412 of the Code had an accumulated  funding
         deficiency  (as  defined in Section 302 of ERISA and Section 412 of the
         Code),  whether or not waived,  as of the last day of the most recently
         completed fiscal year of such Plan;

                  (x) no material  liability to the PBGC has been or is expected
         by Iron Mountain or any Iron Mountain Subsidiary to be incurred by Iron
         Mountain or any Iron Mountain Subsidiary with respect to any such Plan,
         and there has been no event or condition which presents a material risk
         of termination of any such Plan by the PBGC; and

                  (xi)  except as set forth in Section  4.10(a)(xi)  of the Iron
         Mountain  Disclosure  Schedule  (which  entry,  if  applicable,   shall
         indicate the present value of accumulated plan  liabilities  calculated
         in a manner  consistent with FAS 106 and actual annual expense for such
         benefits  for  each of the  last  two (2)  years)  or  pursuant  to the
         provisions of COBRA,  which  provisions  have been complied with in all
         material  respects,   neither  Iron  Mountain  nor  any  Iron  Mountain
         Subsidiary  maintains  any Plan that  provides  benefits  described  in
         Section  3(1) of ERISA to any  former  employees  or  retirees  of Iron
         Mountain or any of its Subsidiaries.

         (b)  Except  as  disclosed  in  Section  4.10(b)  of the Iron  Mountain
Disclosure  Schedule,  neither Iron Mountain nor any Iron Mountain Subsidiary is
or ever has been a party to any Multiemployer  Plan or made contributions to any
such plan.

         Section 4.11. Authorized and Outstanding Capital Stock.

         (a) As of September 30, 1999, the authorized  and  outstanding  capital
stock of Iron Mountain was as set forth in Section  4.11(a) of the Iron Mountain
Disclosure  Schedule.  All of such  outstanding  capital  stock  has  been  duly
authorized  and  validly  issued,  is fully  paid and  nonassessable  and is not
subject to any preemptive or similar rights. From September 30, 1999 through the
date of this Agreement, Iron Mountain has not issued any shares of capital stock
other than  issuances  of Iron  Mountain  Common  Stock in  accordance  with the
exercise  of Iron  Mountain  Options  or under  the Iron  Mountain  ESPP Plan in
accordance  with past practice.  Shares of Iron Mountain Common Stock issued and
outstanding on the record date for the Iron Mountain Special Meeting will be the
only class of capital stock eligible to vote on this  Agreement,  the Merger and
the  Transactions.  Except as set forth in Section 4.11(a) or 4.1(d) of the Iron
Mountain Disclosure Schedule, (i) there


<PAGE>

                                       26

is neither  outstanding  nor has Iron Mountain or any Iron  Mountain  Subsidiary
agreed  to grant  or  issue  any  shares  of its  capital  stock,  other  equity
interests,  any Option Security,  Convertible  Security or Voting Debt, and (ii)
neither Iron Mountain nor any Iron Mountain Subsidiary is a party to and neither
Iron  Mountain  nor any Iron  Mountain  Subsidiary  is bound by any  Contractual
Obligation,  put or  commitment  pursuant to which it is  obligated to purchase,
redeem or otherwise acquire any shares of capital stock, other equity interests,
any Option Security,  Convertible Security or Voting Debt. Neither Iron Mountain
nor any Iron Mountain  Subsidiary has any Voting Debt  outstanding.  Between the
date of this Agreement and the Closing,  except as set forth in Section  4.11(a)
of the Iron Mountain Disclosure  Schedule,  neither Iron Mountain nor any of its
Subsidiaries  will issue,  sell or purchase or agree to issue,  sell or purchase
any capital stock,  other equity  interests,  any Option  Security,  Convertible
Security or Voting Debt of Iron Mountain or any of its  Subsidiaries,  except to
the extent required or permitted pursuant to the terms hereof. All of the issued
and outstanding shares of Iron Mountain's capital stock and each Option Security
or  Convertible  Security  of Iron  Mountain  were issued and sold or granted in
compliance with the Securities Act and applicable state securities laws.

         (b)  As of  September  30,  1999,  (i)  Option  Securities  to  acquire
2,120,795  shares of Iron  Mountain  Common  Stock were  outstanding  under Iron
Mountain's  1995 Stock  Incentive  Plan (the "Iron  Mountain 1995 Option Plan"),
including  in such  number  Option  Securities  which were then  exercisable  to
acquire 929,631 shares of Iron Mountain Common Stock;  (ii) Option Securities to
acquire 264,227 shares of Iron Mountain Common Stock were outstanding  under the
Iron  Mountain/ATSI  1995  Stock  Option  Plan (the "Iron  Mountain/ATSI  Option
Plan"),  including in such number Option  Securities which were then exercisable
to  acquire  222,297  shares  of Iron  Mountain  Common  Stock;  (iii) no Option
Securities  to acquire  shares of Iron  Mountain  Common Stock were  outstanding
under Iron Mountain's 1998 Employee Stock Purchase Plan (the "Iron Mountain ESPP
Plan" and,  together with the Iron Mountain 1995 Option Plan, the "Iron Mountain
Option  Plans");  and (iv)  531,350  shares of Iron  Mountain  Common Stock were
reserved for future issuance  pursuant to Option Securities which may be granted
under the Iron  Mountain  1995 Option Plan and 375,000  shares of Iron  Mountain
Common Stock were  reserved for future  issuance  pursuant to Option  Securities
which may be granted under the Iron Mountain ESPP Plan.  From September 30, 1999
through  the  date of  this  Agreement,  neither  Iron  Mountain  nor any of its
Subsidiaries  has issued any Option  Securities,  other than  Option  Securities
under the Iron  Mountain ESPP Plan in accordance  with past  practice.  The Iron
Mountain  Option Plans  constitute  the only plans or  arrangements  pursuant to
which Option  Securities or Convertible  Securities to acquire shares of capital
stock of Iron Mountain or any of its  Subsidiaries  are  currently  outstanding.
Other  than as set forth in  Section  4.11(b)  of the Iron  Mountain  Disclosure
Schedule,  neither  the  execution  and  delivery  of  this  Agreement  nor  the
consummation  of the Merger or the  Transactions  are events which will cause an
acceleration of the exercise or vesting  schedule of any such Option Security or
Convertible  Security.  All shares of Iron  Mountain  capital  stock  subject to
issuance under an Option  Security or  Convertible  Security of Iron Mountain or
any of its  Subsidiaries  will be,  upon  issuance  on the terms and  conditions
specified in such Option Security or Convertible Security, validly issued, fully
paid and nonassessable.

         (c) There are no voting  trusts  or other  arrangements  to which  Iron
Mountain or any Iron  Mountain  Subsidiary is a party with respect to the voting
of capital stock of Iron Mountain or any Iron Mountain Subsidiary.

<PAGE>

                                       27

         Section 4.12. Employment Arrangements.

         (a) Neither Iron  Mountain nor any Iron  Mountain  Subsidiary is now or
during  the  past  three  (3)  years  (at the time it was a  Subsidiary  of Iron
Mountain) has been subject to or involved in or, to Iron  Mountain's  knowledge,
threatened  in writing  with any union  elections,  petitions  therefor or other
organizational or recruiting activities,  except as described in Section 4.12(a)
of the Iron Mountain Disclosure Schedule. Except as set forth in Section 4.12(a)
of the Iron Mountain Disclosure Schedule, none of the employees of Iron Mountain
and its Subsidiaries are now, or during the past three (3) years (at the time it
was a Subsidiary of Iron Mountain) have been,  represented by any labor union or
other employee collective bargaining organization or are parties to any labor or
other  collective  bargaining  agreement,  and there are no pending  grievances,
disputes  or  controversies  with any  union or any  other  employee  collective
bargaining  organization  of such employees,  or, to Iron Mountain's  knowledge,
threats in writing of  strikes,  work  stoppages  or  slowdowns  or any  pending
demands for collective  bargaining by any union or other such organization or by
any other  employees,  except as would not,  individually  or in the  aggregate,
reasonably be expected to have an Adverse Effect on Iron Mountain.

         (b)  Except  as set  forth in  Section  4.12(b)  of the  Iron  Mountain
Disclosure  Schedule,  no  employee  of  Iron  Mountain  or  any  Iron  Mountain
Subsidiary will accrue or receive or is entitled to accrue or receive additional
benefits,  service or accelerated rights to payments of benefits,  including the
right to receive any parachute payment,  as defined in Section 280G of the Code,
or become entitled to severance,  termination allowance or similar payments as a
result of this Agreement, the Merger or the Transactions.

         Section 4.13. Material Agreements. To Iron Mountain's knowledge, listed
on  Section  4.13 of the Iron  Mountain  Disclosure  Schedule  are all  Material
Agreements to which Iron Mountain or any Iron Mountain  Subsidiary is a party or
to which it or any of its  property  is subject  or bound.  True,  complete  and
correct  copies of each of the Material  Agreements  have been furnished by Iron
Mountain to Pierce Leahy. All of the Material Agreements are valid,  binding and
legally  enforceable  obligations  of Iron  Mountain  and,  to  Iron  Mountain's
knowledge, the other parties thereto (subject to the Enforceability Exceptions),
except  where  the lack of  enforceability  would  not,  individually  or in the
aggregate,  reasonably be expected to have an Adverse  Effect on Iron  Mountain.
Except as set forth in Section 4.13 of the Iron  Mountain  Disclosure  Schedule,
Iron  Mountain  and each Iron  Mountain  Subsidiary  have duly  complied  in all
material  respects  with  all of the  terms  and  conditions  of  each  Material
Agreement and have not done or performed,  or failed to do or perform (and there
is no pending or, to the  knowledge of Iron  Mountain,  threatened  (in writing)
Claim that Iron  Mountain or any Iron Mountain  Subsidiary  has not so complied,
done and  performed  or failed to do and  perform)  any act the  effect of which
would be to  invalidate  or  provide  grounds  for the other  party  thereto  to
terminate  (with or  without  notice,  passage  of time or both)  such  Material
Agreement  or impair the rights or  benefits,  or  increase  the costs,  of Iron
Mountain or any Iron Mountain Subsidiary,  under any of the Material Agreements,
except as would not  reasonably  be  expected  to have,  individually  or in the
aggregate,  an Adverse Effect on Iron  Mountain.  Except as set forth in Section
4.13 of the  Iron  Mountain  Disclosure  Schedule,  neither  the  execution  and
delivery of this Agreement or any Collateral Document executed or required to be
executed  pursuant hereto or thereto,  nor the consummation of the Transactions,
nor compliance  with the terms,  conditions and provisions  hereof or thereof by
Iron  Mountain  will  conflict  with,  or result in a breach or violation of, or
constitute a default  under,  or permit the  acceleration  of any  obligation or
liability in, or but for


<PAGE>

                                       28

any requirement of giving of notice or passage of time or both would  constitute
such a conflict with,  breach or violation of, or default  under,  or permit any
such acceleration in, any Material Agreement.

         Section  4.14.  Ordinary  Course  of  Business.  Except as set forth in
Section 4.14 of the Iron Mountain  Disclosure  Schedule or disclosed in the Iron
Mountain SEC Reports,  since the date of the most recent  audited Iron  Mountain
Financial  Statements included in the Iron Mountain SEC Reports through the date
of this  Agreement,  Iron  Mountain and its  Subsidiaries  have  operated  their
respective businesses only in the ordinary and usual course and in substantially
the same manner as previously conducted and there has not been:

                  (i) any  damage,  destruction  or  loss  with  respect  to the
         properties  or  assets of Iron  Mountain  or its  Subsidiaries  whether
         covered  by  insurance  or not,  which has had or would  reasonably  be
         expected to have,  individually or in the aggregate,  an Adverse Effect
         with respect to Iron Mountain;

                  (ii) any other change,  occurrence or circumstance that had or
         would  reasonably be expected to have an Adverse Effect with respect to
         Iron Mountain;

                  (iii)  any  change  to any  accounting  methods  used  by Iron
         Mountain, unless required in accordance with GAAP;

                  (iv)  any  declaration  or  payment  of any  Distributions  in
         respect of the outstanding  shares of capital stock of Iron Mountain or
         any of its  Subsidiaries  (other  than  dividends  declared  or paid by
         wholly-owned Subsidiaries);

                  (v)  any  split,   combination  or  reclassification  of  Iron
         Mountain's  capital stock or any issuance of shares of capital stock of
         Iron  Mountain or any Iron  Mountain  Subsidiary or any other change in
         the  authorized  capitalization  of Iron  Mountain or any Iron Mountain
         Subsidiary,  except as  contemplated  or permitted by this Agreement or
         pursuant  to  employee  benefit  plans,  programs  or  arrangements  in
         existence on the date of this Agreement;

                  (vi) any  repurchase  or redemption by Iron Mountain of shares
         of its  capital  stock or any  issuance  by Iron  Mountain of any other
         securities  in  exchange or in  substitution  for shares of its capital
         stock  except   pursuant  to  employee   benefit  plans,   programs  or
         arrangements  in  existence  on the  date  of  this  Agreement,  in the
         ordinary course of business consistent with past practice;

                  (vii)  any  grant  or  award  of  any  Option   Securities  or
         Convertible Securities or other rights to acquire any shares of capital
         stock or other  equity  interests of Iron  Mountain or any  Subsidiary,
         except  as  contemplated  or  permitted  by this  Agreement  or  except
         pursuant  to  employee  benefit  plans,  programs  or  arrangements  in
         existence  on the date of this  Agreement,  in the  ordinary  course of
         business consistent with past practice; or

                  (viii) any sale or other  disposal of, or any contract to sell
         or otherwise dispose of, any of its properties or assets, other than in
         the ordinary course of business.

<PAGE>

                                       29

         Section 4.15. Broker or Finder. Other than Bear, Stearns & Co. Inc., no
Person  assisted in or brought  about the  negotiation  of this  Agreement,  the
Merger or the  subject  matter of the  Transactions  in the  capacity of broker,
agent or finder or in any  similar  capacity  on behalf of Iron  Mountain  or is
entitled  to any  brokerage,  finder's  or other  fee or  commission  from  Iron
Mountain in  connection  with the  Transactions.  Iron  Mountain has  heretofore
furnished to Pierce Leahy a complete and correct copy of all agreements  between
Iron Mountain and Bear,  Stearns & Co. Inc.  pursuant to which such Person would
be entitled to payment relating to the Transactions.

         Section 4.16. Environmental Matters.

         (a)  Except  as set  forth in  Section  4.16(a)  of the  Iron  Mountain
Disclosure  Schedule,  Iron Mountain and its Subsidiaries have complied with all
applicable  Environmental  Laws except  where the failure to comply would not be
reasonably  expected  to have an Adverse  Effect on Iron  Mountain.  There is no
pending or, to Iron  Mountain's  knowledge,  threatened  (in writing),  civil or
criminal  Legal  Actions,  written  notice of violation,  formal  administrative
proceeding or  investigation,  inquiry or  information  request by any Authority
relating  to  any  Environmental  Law  involving  Iron  Mountain  or  any of its
Subsidiaries  or any of their  properties,  which would,  individually or in the
aggregate,  not  reasonably  be  expected  to have  an  Adverse  Effect  on Iron
Mountain.

         (b)  Except  as set  forth in  Section  4.16(b)  of the  Iron  Mountain
Disclosure Schedule, there have been no releases of any Hazardous Materials into
the  environment  by  Iron  Mountain  or any of its  Subsidiaries,  or,  to Iron
Mountain's  knowledge,  by any other party at any parcel of real property or any
facility formerly or currently owned, operated or controlled by Iron Mountain or
any of its  Subsidiaries  which would  reasonably be expected to have an Adverse
Effect on Iron Mountain.

         (c) Section 4.16(c) of the Iron Mountain  Disclosure Schedule (which in
accordance with Section 5.16 hereof,  will be delivered  within thirty (30) days
after the date of this  Agreement)  sets forth all site  assessments,  audits or
other  investigations  that have been conducted by or on behalf of Iron Mountain
or  any  Iron  Mountain  Subsidiary  within  the  last  three  (3)  years  as to
environmental  matters at any property  owned,  leased,  operated or occupied by
Iron Mountain or any Iron Mountain Subsidiary.

         Section 4.17. Board Action; Fairness Opinion.

         (a) The Board of  Directors  of Iron  Mountain at a meeting duly called
and held, has by unanimous vote of those directors present (who constituted 100%
of the  directors  then in office) (i)  determined  that this  Agreement and the
Transactions,  including the Merger,  are advisable to and in the best interests
of the Iron Mountain  Stockholders  and has approved the same, and (ii) resolved
to recommend that the holders of the shares of Iron Mountain  Common Stock adopt
this Agreement and the Transactions, including the Merger.

         (b) Iron Mountain has received the opinion of Bear, Stearns & Co. Inc.,
dated as of October 20, 1999, to the effect that,  as of the date  thereof,  the
"Exchange Ratio" (as defined in such opinion)  equivalent to 1.10 shares of Iron
Mountain  Common  Stock  per share of Pierce  Leahy  Common  Stock to be paid in
connection  with the  Merger is fair,  from a  financial  point of view,  to the
stockholders of Iron Mountain.  A signed, true and complete copy of such opinion
has been delivered to Pierce Leahy or will be promptly delivered to Pierce Leahy
by Iron Mountain.


<PAGE>
                                       30


         Section  4.18.  Materiality.  The matters and items  excluded  from the
representations  and  warranties  set forth in this  Article by operation of the
materiality  exceptions  and  materiality   qualifications   contained  in  such
representations  and warranties,  in the aggregate for all such excluded matters
and items,  are not and would not  reasonably  be expected to be Adverse to Iron
Mountain.

                                   ARTICLE 5.

                              ADDITIONAL COVENANTS

         Section 5.1.      Access to Information; Confidentiality.

         (a) Upon reasonable notice,  each Party shall afford to the other Party
and their  respective  Representatives  full access during normal business hours
throughout  the period  prior to the  Effective  Time to all of its  properties,
books,  contracts  (other  than  customer  contracts),  commitments  and records
(including  without  limitation  Tax Returns)  and,  during such  period,  shall
furnish  promptly to one another (i) a copy of each  report,  schedule and other
document filed or received by either of them pursuant to the requirements of any
Applicable Law (including  without  limitation federal or state securities laws)
or filed by it or any of its Subsidiaries  with any Authority in connection with
the Transactions or which would reasonably be expected to have an Adverse Effect
on such  Party and (ii)  such  other  information  concerning  their  respective
businesses,  properties and personnel as Pierce Leahy or Iron  Mountain,  as the
case may be, shall  reasonably  request  (other than  customer  contracts or the
pricing  thereof).  Pierce Leahy and Iron  Mountain  acknowledge  that they have
heretofore  executed a  confidentiality  agreement,  dated  October 4, 1999 (the
"Confidentiality Agreement"),  which separately and as incorporated herein shall
remain in full force and effect  after and  notwithstanding  the  execution  and
delivery of this Agreement,  and that information  obtained from Pierce Leahy by
Iron Mountain or its  Representatives or by Pierce Leahy or its  Representatives
from  Iron  Mountain,  pursuant  to this  Section  5.1(a),  the  Confidentiality
Agreement   or   otherwise,   shall  be  subject  to  the   provisions   of  the
Confidentiality Agreement.

         (b)  Subject  to  the  terms  and  conditions  of  the  Confidentiality
Agreement,  Iron Mountain and Pierce Leahy may disclose such  information as may
be  necessary  in  connection   with  seeking  all   Governmental   and  Private
Authorizations or that is required by Applicable Law or the rules of the NYSE to
be disclosed. In the event that this Agreement is terminated,  Iron Mountain and
Pierce Leahy shall each  promptly  redeliver  all  non-public  written  material
provided  pursuant to this Section or any other  provision of this  Agreement or
otherwise  in  connection  with the  Merger and the  Transactions  and shall not
retain any copies,  extracts or other  reproductions in whole or in part of such
written  material  other  than one copy  thereof  which  shall be  delivered  to
independent counsel for such party.

         (c) No  investigation  pursuant to this  Section  5.1 shall  affect any
representation  or  warranty  in  this  Agreement  of any  Party  hereto  or any
condition to the obligations of the Parties hereto.

         Section  5.2.  Conduct of the  Business  of Pierce  Leahy  Pending  the
Merger.  Between the date of this  Agreement and the Closing Date,  Pierce Leahy
will, and will ensure that each of its  Subsidiaries  will (except (i) as may be
described on Section 5.2 of the Pierce Leahy Disclosure


<PAGE>

                                       31

Schedule,  (ii) as may be required or expressly contemplated or permitted by the
terms of this Agreement, or (iii) as may be consented to by Iron Mountain, which
consent shall not be unreasonably withheld or delayed):

                  (i) operate its  business in the normal,  usual and  customary
         manner  in the  ordinary  course of  business,  consistent  with  prior
         practice,  and  use  all  reasonable  efforts,   consistent  with  past
         practice, to maintain and preserve its business  organization,  assets,
         employees and advantageous business relationships;

                  (ii) not sell or  otherwise  dispose of or contract to sell or
         otherwise dispose of any material amount of properties or assets, other
         than in the ordinary course of business consistent with past practice;

                  (iii) not  create or permit to be  created  any Lien on any of
         its  properties,  except  such  Liens  which,  individually  or in  the
         aggregate,  would not  reasonably be expected to have an Adverse Effect
         on Pierce Leahy;

                  (iv) except in the  ordinary  course of  business,  consistent
         with prior practice,  not increase the  compensation or fringe benefits
         payable  or to  become  payable  to  any of  its  directors,  officers,
         employees,  advisers,  consultants,  salesmen  or agents  or  otherwise
         alter, modify or change the terms of their employment or engagement, or
         grant any severance or  termination  pay not  currently  required to be
         paid under existing  severance  plans to, or enter into any employment,
         consulting or severance agreement with, any present or former director,
         officer or other  employee of Pierce Leahy or any of its  Subsidiaries,
         or establish,  adopt,  enter into or amend or terminate any  collective
         bargaining, bonus, profit sharing, thrift, compensation,  stock option,
         restricted   stock,   pension,   retirement,   deferred   compensation,
         employment,  termination,  severance or other plan,  agreement,  trust,
         fund,  policy or arrangement for the benefit of directors,  officers or
         employees;

                  (v) not settle any pending or threatened material Legal Action
         or  any  other  Legal  Action  which  relates  to  the  Merger  or  the
         Transactions;

                  (vi) not (A) enter into,  amend or terminate  (1) any Material
         Agreement,  except in the ordinary course of business,  consistent with
         prior  practice,  in  accordance  with  the  terms  thereof  and  which
         individually  or in the aggregate  would not  reasonably be expected to
         have  an  Adverse  Effect  on  Pierce  Leahy,  or (2)  any  Contractual
         Obligation or  transaction  with an Affiliate that would be required to
         be disclosed  pursuant to Item 404 of Regulation S-K promulgated by the
         SEC,  or (B)  enter  into or amend  any  Contractual  Obligation  which
         restrains,  limits or impedes  Pierce Leahy or any of its  Subsidiaries
         (or,  after  the  Merger,  the  Surviving  Corporation  or  any  of its
         Subsidiaries)  from  freely  engaging  in  any  business  or  competing
         anywhere in the world  (including,  without  limitation,  in connection
         with any joint  venture or similar  Entity that provides for such joint
         venture or Entity to be the  exclusive  provider of records  management
         services in a particular geographic area);

                  (vii) not,  directly  or  indirectly,  (A) sell or transfer or
         agree to sell or  transfer  any shares of Pierce  Leahy  Common  Stock,
         Pierce Leahy Preferred Stock or capital stock or other equity interests
         of it or any of its  Subsidiaries  directly or indirectly  beneficially
         owned

<PAGE>

                                       32

         by Pierce Leahy or any of its  Subsidiaries;  or (B) split,  combine or
         reclassify the Pierce Leahy Common Stock,  Pierce Leahy Preferred Stock
         or any other outstanding  capital stock or other equity interests of it
         or any of Pierce Leahy's Subsidiaries;

                  (viii)  not,  directly  or  indirectly,  (A) amend its Organic
         Documents; (B) issue, grant or sell any Option Securities,  Convertible
         Securities, shares of capital stock or other equity interests of Pierce
         Leahy or its Subsidiaries or any other ownership interests  (including,
         without limitation,  stock appreciation rights or phantom stock), other
         than (1) shares of Pierce Leahy  Common Stock  reserved for issuance on
         the date of this  Agreement  pursuant to the  exercise of Pierce  Leahy
         Options  outstanding on the date of this Agreement,  (2) dividends paid
         in kind in  accordance  with the terms of the  Pierce  Leahy  Preferred
         Stock,  or (3) shares of  preferred  stock of Pierce Leahy that satisfy
         the  definition  of  Permitted   Indebtedness   ("Redeemable  Preferred
         Stock");  (C)  incur  any  Indebtedness  other  than  borrowings  under
         existing  agreements  as in  effect on the date of this  Agreement  and
         under  agreements  representing  Permitted  Indebtedness so long as the
         proceeds of such  borrowings are used in a manner  consistent with this
         Section 5.2; or (D) redeem,  purchase or otherwise  acquire directly or
         indirectly  any of its  capital  stock  (other  than the  Pierce  Leahy
         Preferred Stock or Redeemable Preferred Stock);

                  (ix)  not  declare,  set  aside or pay any  Distribution  with
         respect to its capital stock (other than (A) the Stock Dividend, (B) in
         accordance with the terms of the Pierce Leahy Preferred Stock or (C) in
         accordance  with the terms of any Redeemable  Preferred Stock issued in
         accordance with Section 5.2(viii));

                  (x) not  change  any  accounting  methods  used  by it  unless
         required in accordance with GAAP;

                  (xi)  not   acquire   or  agree  to   acquire  by  merging  or
         consolidating with, or by purchasing any of the assets of or equity in,
         or by any other  manner,  any  business of any Person (A) having a fair
         market value  (which  amount  shall  include the maximum  amount of any
         earnout  or  other  contingent   payment)  in  excess  of  $25  million
         individually  or $100 million in the aggregate or (B) that is primarily
         engaged in a line of business  different than those of Pierce Leahy and
         its Subsidiaries, regardless of fair market value; and

                  (xii) not  authorize  or enter into an  agreement to do any of
         the foregoing.

         Section  5.3.  Conduct of the  Business  of Iron  Mountain  Pending the
Merger.  Between the date of this Agreement and the Closing Date,  Iron Mountain
will, and will ensure that each of its  Subsidiaries  will (except (i) as may be
described on Section 5.3 of the Iron Mountain Disclosure  Schedule,  (ii) as may
be  required  or  expressly  contemplated  or  permitted  by the  terms  of this
Agreement,  or (iii) as may be consented to by Pierce Leahy, which consent shall
not be unreasonably withheld or delayed):

                  (i) operate its  business in the normal,  usual and  customary
         manner  in the  ordinary  course of  business,  consistent  with  prior
         practice,  and  use  all  reasonable  efforts,   consistent  with  past
         practice, to maintain and preserve its business  organization,  assets,
         employees and advantageous business relationships;

<PAGE>
                                       33


                  (ii)  except  as  disclosed  in  Section  5.3(ii)  of the Iron
         Mountain  Disclosure  Schedule,  not sell or  otherwise  dispose  of or
         contract  to  sell or  otherwise  dispose  of any  material  amount  of
         properties  or assets,  other than in the  ordinary  course of business
         consistent with past practice;  provided,  however,  that Iron Mountain
         may sell or  otherwise  dispose  of or  contract  to sell or  otherwise
         dispose of any  properties or assets which  generated not more than $50
         million in  revenues  for the  fiscal  year ended  December  31,  1998,
         excluding,  for  purposes of such  calculation,  those  properties  and
         assets  described in Section  5.3(ii) of the Iron  Mountain  Disclosure
         Schedule;

                  (iii) not  create or permit to be  created  any Lien on any of
         its  properties,  except  such  Liens  which,  individually  or in  the
         aggregate,  would not  reasonably be expected to have an Adverse Effect
         on Iron Mountain;

                  (iv) not settle any pending or  threatened  Legal Action which
         relates to the Merger or the Transactions;

                  (v)  not  enter  into,  amend  or  terminate  any  Contractual
         Obligation or  transaction  with an Affiliate that would be required to
         be disclosed  pursuant to Item 404 of Regulation S-K promulgated by the
         SEC;

                  (vi) not,  directly  or  indirectly,  (A) sell or  transfer or
         agree to sell or transfer  any shares of Iron  Mountain  Common  Stock,
         preferred stock or capital stock or other equity interests of it or any
         of its Subsidiaries  directly or indirectly  beneficially owned by Iron
         Mountain  or any of its  Subsidiaries;  provided,  however,  that  Iron
         Mountain or one of its  Subsidiaries may transfer its shares of capital
         stock of, or other equity  interests in, any Subsidiary so long as such
         transaction  would be permitted  under Section  5.3(ii);  or (B) split,
         combine  or  reclassify  the Iron  Mountain  Common  Stock or any other
         outstanding  capital  stock or other  equity  interests of it or any of
         Iron Mountain's Subsidiaries;

                  (vii)  not,  directly  or  indirectly,  (A) amend its  Organic
         Documents or (B) issue, grant or sell any Option Securities (other than
         under the Iron Mountain Option Plans),  Convertible Securities,  shares
         of capital  stock or other  equity  interests  of Iron  Mountain or its
         Subsidiaries,  other than (1)  issuances by Iron Mountain of additional
         shares of Iron  Mountain  Common  Stock in an  aggregate  amount not to
         exceed an  additional  ten percent  (10%) of the number of  outstanding
         shares of Iron Mountain  Common Stock as of the date of this  Agreement
         in  connection  with  acquisitions  by  Iron  Mountain  or  any  of its
         Subsidiaries,  (2) shares of Iron Mountain Common Stock pursuant to the
         exercise of Iron Mountain  Options under the Iron Mountain Option Plans
         and  (3)  shares  of  preferred  stock  of  Iron  Mountain  that do not
         represent Option Securities, Convertible Securities or Voting Debt);

                  (viii) not  declare,  set aside or pay any  Distribution  with
         respect to its capital stock (other than in  accordance  with the terms
         of any  preferred  stock issued in  accordance  with  Section  5.3(vii)
         hereof);

<PAGE>
                                       34

                  (ix) not  change  any  accounting  methods  used by it  unless
         required in accordance with GAAP;

                  (x)  not   acquire   or  agree  to   acquire   by  merging  or
         consolidating with, or by purchasing any of the assets of or equity in,
         or by any other manner,  businesses or Persons (A) having a fair market
         value (which amount shall include the maximum  amount of any earnout or
         other contingent payment) in excess of $200 million in the aggregate or
         (B) that are  primarily  engaged in a line of business  different  than
         those of Iron Mountain and its Subsidiaries,  regardless of fair market
         value; and

                  (xi) not authorize or enter into an agreement to do any of the
         foregoing.

         Section 5.4. Control of Operations. Nothing contained in this Agreement
shall give to Pierce Leahy or Iron Mountain,  directly or indirectly,  rights to
control or direct the  operations of Iron Mountain or Pierce Leahy,  as the case
may be, prior to the Effective Time. Prior to the Effective Time, each of Pierce
Leahy and Iron Mountain shall exercise, consistent with the terms and conditions
of this Agreement, complete control and supervision of its operations.

         Section 5.5.      Agreement to Cooperate.

         (a) Each of the Parties shall use its reasonable  best efforts to take,
or cause to be taken,  all  actions  and to do, or cause to be done,  all things
necessary, proper or advisable under Applicable Law to consummate the Merger and
make effective the Transactions, including using its reasonable best efforts (i)
to prepare and file with the  applicable  Authorities as promptly as practicable
after the execution of this Agreement all requisite  applications and amendments
thereto,  together with related  information,  data and  exhibits,  necessary to
request issuance of orders approving the Merger and the Transactions by all such
applicable Authorities,  each of which must be obtained or become final in order
to satisfy the condition  applicable to it set forth in Section 6.1(c);  (ii) to
obtain all necessary or appropriate  waivers,  consents and approvals;  (iii) to
effect all necessary  registrations,  filings and submissions (including without
limitation filings under federal or state securities laws or the HSR Act and any
other  submissions  requested by the SEC, the FTC or the DOJ);  and (iv) to lift
any  injunction or other legal bar to the Merger and the  Transactions.  Each of
the Parties  recognizes that the consummation of the Merger and the Transactions
is subject to the preacquisition  notification requirements of the HSR Act. Each
agrees  that it will file  with the  Antitrust  Division  of the DOJ and the FTC
within fifteen (15) days of the date of this Agreement a Notification and Report
Form  in  a  manner  so  as  to  constitute   substantial  compliance  with  the
notification requirements of the HSR Act. Each Party covenants and agrees to use
its reasonable  best efforts to achieve the prompt  termination or expiration of
any waiting period or any extension  thereof under the HSR Act and to obtain any
clearance  required under the HSR Act for the consummation of the Merger,  which
efforts,  for purposes of this  Agreement,  shall not require either Party,  the
Surviving Corporation or any of their respective Subsidiaries in order to obtain
any  consent  or  clearance  from the DOJ,  FTC or any other  Authority  to hold
separate,  sell or otherwise dispose of any assets,  the effect of any of which,
in the  reasonable  judgment of such Party,  would be to  materially  impair the
value of the Merger to such Party.

         (b) Pierce  Leahy will use its  reasonable  best efforts on or prior to
the Closing  Date to obtain the  satisfaction  of the  conditions  specified  in
Sections 6.1 and 6.2. Iron Mountain will use

<PAGE>

                                       35

its  reasonable  best  efforts  on or prior to the  Closing  Date to obtain  the
satisfaction  of the  conditions  applicable to it specified in Sections 6.1 and
6.3.

         (c) The parties shall  cooperate  with one another in the  preparation,
execution  and filing of all  Returns,  questionnaires,  applications,  or other
documents  regarding any real property transfer or gains,  sales, use, transfer,
value added, stock transfer and stamp Taxes or any Plan, Benefit  Arrangement or
employment arrangement,  any transfer,  recording,  registration and other fees,
and any similar Taxes which become payable in connection  with the  Transactions
that are required or permitted to be filed on or before the Effective Time.

         (d) Iron Mountain shall cause its  independent  accountants,  and shall
use its reasonable best efforts to cause any other independent  accountants that
have audited any financial  statements  of businesses  acquired by Iron Mountain
that  are  required  to  be  included  or   incorporated  by  reference  in  the
Registration Statement, to cooperate with Pierce Leahy and to consent to the use
of their audit reports on audited financial statements for Iron Mountain or such
other businesses for inclusion in the Registration  Statement.  Without limiting
the generality of the foregoing,  Iron Mountain  agrees that it will (i) consent
to the use of such audited financial statements in any registration statement or
other  document  filed by Pierce Leahy under the  Securities Act or the Exchange
Act,  and (ii)  execute  and  deliver,  and cause its  officers  to execute  and
deliver,  such   "representation"   letters  as  are  customarily  delivered  in
connection  with  audits  and as  Pierce  Leahy's  independent  accountants  may
reasonably request under the circumstances.

         (e)  Pierce  Leahy  and Iron  Mountain  (i) shall  supply  consolidated
financial  statements for it and, to the extent  required  under  Regulation S-X
under the Securities  Act, any acquired  businesses,  (and any and all documents
and  consents  related  thereto)  which  comply  with  Regulation  S-X under the
Securities Act and the applicable published rules and regulations thereunder for
inclusion in any  registration  statement  or other  public  filing of the other
Party under the  Securities  Act and the Exchange  Act,  and any other  offering
circular or document used by Pierce Leahy or Iron Mountain,  as the case may be,
in any  other  offering,  whether  public  or  private,  and (ii)  shall use its
reasonable  best efforts to cause their  respective  independent  accountants to
cooperate  with the other Party in  connection  with the  foregoing  (including,
without  limitation,  using  reasonable  best efforts to cause such  independent
accountants to deliver so-called "comfort letters" and written consents relating
to the foregoing); provided, however, that Pierce Leahy or Iron Mountain, as the
case may be, shall reimburse the other for its reasonable out-of-pocket expenses
incurred in connection  with its compliance with this Section 5.5(e) (other than
with  respect  to any  services  that  would  ordinarily  be  provided  by  such
accountants). Without limiting the generality of the foregoing, Pierce Leahy and
Iron  Mountain  each agrees that it will (i) consent to the use of such  audited
financial  statements in any such registration  statement,  document or circular
and (ii)  execute and  deliver,  and cause its  officers to execute and deliver,
such  "representation"  letters as are customarily  delivered in connection with
audits and as Pierce Leahy's and Iron  Mountain's  independent  accountants  may
reasonably request under the circumstances.

         Section 5.6. Affiliate Agreements; Registration Rights Agreement.

         (a) Prior to the Closing Date,  Iron  Mountain  shall deliver to Pierce
Leahy a letter  identifying  all Persons who are, at the time this  Agreement is
submitted to the  Stockholders,  "affiliates"  of Iron  Mountain for purposes of
Rule 145 under the Securities Act. Iron Mountain shall

<PAGE>

                                       36

use its reasonable  best efforts to cause each such  "affiliate",  to deliver to
Pierce Leahy on or prior to the Closing Date a written  agreement (an "Affiliate
Agreement") substantially in the form attached hereto as Exhibit 5.6(a).

         (b) Pierce  Leahy agrees that it will  expressly  assume the rights and
obligations   of  Iron  Mountain   under  that  certain   Amended  and  Restated
Registration  Rights  Agreement  dated as of June 12, 1997 among Iron  Mountain,
certain principal  stockholders of Iron Mountain and such other  stockholders of
Iron Mountain as are party thereto (the  "Registration  Rights  Agreement") with
respect to shares of Pierce  Leahy  Common  Stock to be issued in the Merger and
that for  purposes of the  Registration  Rights  Agreement,  Pierce Leahy Common
Stock  shall be  considered  "Registrable  Securities".  Pierce  Leahy  and Iron
Mountain agree that the Registration  Rights Agreement will be amended as of the
Effective  Time to join (the  "Registration  Rights  Agreement  Joinder")  those
Pierce  Leahy  Principal  Shareholders  who  become  party to the  Pierce  Leahy
Shareholders'  Agreement  on or before  November  3, 1999  (together  with their
Permitted Assignees (as defined in the Pierce Leahy  Shareholders'  Agreement)),
with  respect to Subject  Shares (as defined in the Pierce  Leahy  Shareholders'
Agreement),  for the benefit of such Pierce Leahy Principal Shareholders,  which
amendment to the  Registration  Rights  Agreement shall be  substantially in the
form attached hereto as Exhibit 5.6(b).

         Section 5.7. No Solicitation.

         (a)  Pierce   Leahy  shall  not,   nor  shall  it  permit  any  of  its
Representatives (including,  without limitation, any investment banker, attorney
or accountant retained by it) to, initiate,  solicit or facilitate,  directly or
indirectly, any inquiries or the making of any proposal with respect to an Other
Transaction, engage in any discussions or negotiations concerning, or provide to
any other Person any information or data relating to, Pierce Leahy or any of its
Subsidiaries  for the  purposes  of, or  otherwise  cooperate in any way with or
assist or  participate  in,  facilitating  any  inquiries  or the  making of any
proposal which constitutes, or may reasonably be expected to lead to, a proposal
to seek or  effect  an  Other  Transaction,  or agree to or  endorse  any  Other
Transaction;  provided,  however, that, notwithstanding anything to the contrary
in this Agreement,  prior to the approval of this Agreement and the Transactions
by the Pierce  Leahy  Shareholders,  Pierce Leahy may engage in  discussions  or
negotiations with, and may furnish  information  concerning Pierce Leahy and its
Subsidiaries  and their  business,  properties and assets to, a third party who,
without any solicitation, initiation, encouragement,  discussion or negotiation,
directly or indirectly,  by or with Pierce Leahy, any of its Subsidiaries or any
of their respective Representatives,  or in furtherance thereof makes a written,
bona fide  proposal  regarding an Other  Transaction  that is not subject to any
material  contingencies  relating to financing and that is reasonably capable of
being financed and is financially  superior to the  consideration to be received
by the Pierce Leahy  Shareholders  pursuant to the Merger (as determined in good
faith by Pierce  Leahy's  Board of  Directors  after  consultation  with  Pierce
Leahy's financial advisors) if (1) Pierce Leahy's Board of Directors  determines
in good faith,  after  consultation  with Pierce Leahy's  outside legal counsel,
that such action is required for Pierce  Leahy's  Board of Directors to act in a
manner  consistent with its fiduciary  duties under Applicable Law and (2) prior
to furnishing  information  with respect to Pierce Leahy and its Subsidiaries to
such third  party,  Pierce  Leahy shall have  received  from such third party an
executed  confidentiality  agreement in reasonably  customary  form on terms not
more  favorable to such Entity than the terms  contained in the  Confidentiality
Agreement. Notwithstanding the foregoing, the Board of Directors of Pierce Leahy
may take and disclose to the Pierce Leahy Shareholders a position with regard to


<PAGE>

                                       37

a tender offer or exchange  offer to the extent  required by Rule 14e-2(a) under
the Exchange Act. In the event of a purported  termination  of this Agreement by
Pierce  Leahy  pursuant  to  Section  7.1(c)(ii),  any  violation  prior to such
termination  of the  restrictions  set forth in the  preceding  sentence  (after
giving  effect to the proviso  contained  therein) by any  investment  banker or
financial  advisor  retained  by Pierce  Leahy,  whether  or not such  Person is
purporting  to act on  behalf  of  Pierce  Leahy or any of its  Subsidiaries  or
otherwise,  shall be deemed to  constitute  a breach of this  Section  5.7(a) by
Pierce Leahy.  Pierce Leahy shall promptly  advise Iron Mountain of, and (unless
the Board of  Directors  of Pierce  Leahy  concludes  that  such  disclosure  is
inconsistent  with its fiduciary  duties under  Applicable Law)  communicate the
material  terms of, any  proposal it may receive,  or any  inquiries it receives
which may reasonably be expected to lead to such a proposal relating to an Other
Transaction,  and the  identity  of the Person  making it.  Pierce  Leahy  shall
further  advise Iron  Mountain of the status and changes in the  material  terms
(unless the Board of Directors of Pierce Leahy concludes that such disclosure is
inconsistent  with  its  fiduciary  duties  under  Applicable  Law) of any  such
proposal or inquiry (or any  amendment to any of them).  During the term of this
Agreement,  except as contemplated  or permitted by this Section 5.7(a),  Pierce
Leahy  shall  not  enter  into  any  agreement  (other  than  a  confidentiality
agreement), whether oral or written and whether or not legally binding, with any
Person that provides for, or in any way facilitates, an Other Transaction.

         (b)  Iron  Mountain   shall  not,  nor  shall  it  permit  any  of  its
Representatives (including,  without limitation, any investment banker, attorney
or accountant retained by it) to, initiate,  solicit or facilitate,  directly or
indirectly,  any inquiries or the making of any proposal with respect to an Iron
Mountain Transaction,  engage in any discussions or negotiations concerning,  or
provide to any other Person any  information  or data relating to, Iron Mountain
or any of its  Subsidiaries  for the purposes of, or otherwise  cooperate in any
way with or assist or participate in,  facilitating  any inquiries or the making
of any proposal which  constitutes,  or may reasonably be expected to lead to, a
proposal to seek or effect an Iron Mountain Transaction,  or agree to or endorse
any Iron Mountain Transaction; provided, however, that, notwithstanding anything
to the contrary in this  Agreement,  prior to the approval of this Agreement and
the Transactions by the Iron Mountain Stockholders,  Iron Mountain may engage in
discussions or negotiations  with, and may furnish  information  concerning Iron
Mountain and its  Subsidiaries  and their business,  properties and assets to, a
third party who, without any solicitation, initiation, encouragement, discussion
or  negotiation,  directly or indirectly,  by or with Iron Mountain,  any of its
Subsidiaries  or any of  their  respective  Representatives,  or in  furtherance
thereof  makes  a  written,  bona  fide  proposal  regarding  an  Iron  Mountain
Transaction  that is not  subject  to any  material  contingencies  relating  to
financing and that is reasonably  capable of being  financed and is  financially
superior to the  consideration to be received by the Iron Mountain  Stockholders
pursuant to the Merger (as determined in good faith by Iron Mountain's  Board of
Directors after  consultation  with Iron Mountain's  financial  advisors) if (1)
Iron Mountain's Board of Directors  determines in good faith, after consultation
with Iron  Mountain's  outside legal  counsel,  that such action is required for
Iron  Mountain's  Board  of  Directors  to act in a manner  consistent  with its
fiduciary  duties under  Applicable Law and (2) prior to furnishing  information
with respect to Iron  Mountain and its  Subsidiaries  to such third party,  Iron
Mountain  shall have received from such third party an executed  confidentiality
agreement  in  reasonably  customary  form on terms not more  favorable  to such
Entity   than   the   terms   contained   in  the   Confidentiality   Agreement.
Notwithstanding the foregoing,  the Board of Directors of Iron Mountain may take
and  disclose  to the Iron  Mountain  Stockholders  a position  with regard to a
tender offer or exchange offer to the extent required by Rule 14e-2(a) under the
Exchange Act. In the event of a purported termination of this Agreement by Iron

<PAGE>

                                       38

Mountain pursuant to Section 7.1(d)(ii), any violation prior to such termination
of the restrictions set forth in the preceding  sentence (after giving effect to
the proviso  contained  therein) by any investment  banker or financial  advisor
retained by Iron  Mountain,  whether or not such Person is  purporting to act on
behalf of Iron Mountain or any of its Subsidiaries or otherwise, shall be deemed
to constitute a breach of this Section  5.7(b) by Iron  Mountain.  Iron Mountain
shall  promptly  advise  Pierce  Leahy of, and (unless the Board of Directors of
Iron Mountain  concludes that such disclosure is inconsistent with its fiduciary
duties under  Applicable Law) communicate the material terms of, any proposal it
may receive,  or any inquiries it receives  which may  reasonably be expected to
lead to  such a  proposal  relating  to an Iron  Mountain  Transaction,  and the
identity of the Person  making it. Iron  Mountain  shall  further  advise Pierce
Leahy of the  status and  changes in the  material  terms  (unless  the Board of
Directors of Pierce Leahy concludes that such  disclosure is  inconsistent  with
its fiduciary  duties under  Applicable Law) of any such proposal or inquiry (or
any  amendment  to any of them).  During the term of this  Agreement,  except as
contemplated or permitted by this Section 5.7(b),  Iron Mountain shall not enter
into any agreement  (other than a  confidentiality  agreement),  whether oral or
written and whether or not legally  binding,  with any Person that provides for,
or in any way facilitates, an Iron Mountain Transaction.

         (c) In the event  Pierce  Leahy or Iron  Mountain  shall  determine  to
provide any  information or negotiate as described  above,  or shall receive any
offer of the type referred to above, it shall (i) immediately  provide the other
Party a copy of all information provided to the third party, and (ii) inform the
other Party that  information is to be provided,  that  negotiations are to take
place or that an offer has been received, as the case may be.

         Section 5.8. Directors' and Officers' Indemnification and Insurance.

         (a) From and after the Effective Time, the Surviving  Corporation shall
indemnify,  defend and hold  harmless each Person who is now, or has been at any
time prior to the date of this  Agreement or who becomes  prior to the Effective
Time,  an  officer  or  director  of  Pierce  Leahy  or any of its  Subsidiaries
(collectively,  the "Indemnified  Parties")  against all Claims or amounts that,
with the approval of the Surviving  Corporation as to settlements only, are paid
in settlement of or otherwise in connection  with any Claim based in whole or in
part on or  arising  in whole or in part out of the fact that such  Person is or
was a  director  or  officer  of  Pierce  Leahy or any of its  Subsidiaries  and
pertaining  to any  matter  existing  or arising  out of  actions  or  omissions
occurring at or prior to the Effective Time (including,  without limitation, any
Claims arising out of this Agreement,  the Merger or any  Transaction),  whether
asserted or claimed  prior to, at or after the  Effective  Time, in each case to
the fullest  extent  currently  provided  under Pierce Leahy's or the applicable
Subsidiary's   Organic  Documents  (but  only  to  the  extent  permitted  under
Applicable  Law),  and shall pay any  expenses,  as incurred,  in advance of the
final  disposition of any such action or proceeding to each Indemnified Party to
the fullest  extent  permitted  under  Applicable  Law,  upon  receipt  from the
Indemnified  Party to whom expenses are advanced of an undertaking to repay such
advances to the extent  required  under  Applicable  Law.  Without  limiting the
foregoing, in the event any such Claim is brought against any of the Indemnified
Parties,  such Indemnified  Parties may retain counsel (including local counsel)
satisfactory to them and which shall be reasonably satisfactory to the Surviving
Corporation,  and the Surviving  Corporation  shall pay all reasonable  fees and
expenses of such counsel for such Indemnified  Parties.  The Indemnified Parties
as a group shall retain only one law firm (plus  appropriate  local  counsel) to
represent them with respect to each such Claim unless there is, as determined by
counsel to the Indemnified Parties, under applicable

<PAGE>

                                       39

standards of professional  conduct,  a conflict or a reasonable  likelihood of a
conflict  on any  significant  issue  between the  positions  of any two or more
Indemnified  Parties, in which event such Indemnified Party shall be entitled to
retain separate legal counsel at the expense of the Surviving Corporation.

         (b) Pierce Leahy,  Iron Mountain and the  Surviving  Corporation  shall
maintain Pierce Leahy's existing  officers' and directors'  liability  insurance
policy  for a period  of not less than six (6) years  after  the  Closing  Date;
provided, (i) that the Surviving Corporation may substitute therefor policies of
substantially similar coverage and amounts containing terms no less advantageous
to such former  directors  or officers and (ii) if the  existing  officers'  and
directors'  liability  insurance expires or is canceled during such period,  the
Surviving Corporation will obtain substantially similar officers' and directors'
liability  insurance to the extent  available.  Pierce  Leahy and Iron  Mountain
agree that the  officers  and  directors of Pierce Leahy on the Closing Date and
their  respective  heirs  and  legal   representatives   shall  be  third  party
beneficiaries of this Section 5.8.

         (c) In the event the Surviving Corporation or its successors or assigns
(i)  consolidates  with or  merges  into any other  Person  and shall not be the
continuing or surviving corporation or Entity of such consolidation or merger or
(ii)  transfers all or  substantially  all of its  properties  and assets to any
Person,  then and in each such case, proper provisions shall be made so that the
successors and assigns of the Surviving Corporation shall assume the obligations
set forth in this Section 5.8.

         Section 5.9.  Notification  of Certain  Matters.  Each Party shall give
prompt written notice to the other of the  occurrence or  non-occurrence  of any
Event the occurrence or  non-occurrence of which would be likely to cause in any
material respect (i) any representation or warranty made by it contained in this
Agreement to be untrue or  inaccurate,  (ii) any change to be made in the Pierce
Leahy Disclosure Schedule or the Iron Mountain Disclosure Schedule,  as the case
may be, or (iii) any failure of Pierce Leahy or Iron  Mountain,  as the case may
be,  to  comply  with or  satisfy,  or be able to comply  with or  satisfy,  any
material covenant, condition or agreement to be complied with or satisfied by it
hereunder;  provided,  however, that the delivery of any notice pursuant to this
Section 5.9 shall not limit or otherwise affect the remedies available hereunder
to the Party receiving such notice.

         Section 5.10. Public Announcements.  Until the Closing, or in the event
of termination of this Agreement, each party shall consult with the other before
issuing any press release or otherwise making any public statements with respect
to this  Agreement,  the Merger or any  Transaction and shall not issue any such
press release or make any such public statement without the prior consent of the
other,   which   consent  shall  not  be   unreasonably   withheld  or  delayed.
Notwithstanding the foregoing, each Party acknowledges and agrees that the other
Party may, without the prior consent of such Party, issue such press releases or
make such public statements as may be required by Applicable Law or by the terms
of any agreement or instrument with any exchange,  including without  limitation
the NYSE,  on which such  Party's  securities  are  listed  (each,  a  "Required
Disclosure"),  in which case,  to the extent  practicable,  the Party making the
Required  Disclosure  will  consult  with,  and  exercise  in  good  faith,  all
reasonable business efforts to agree with the other regarding the nature, extent
and form of such press  release or public  statement,  and,  in any event,  with
prior notice to the other Party.


<PAGE>

                                       40

         Section 5.11. Certain Actions Concerning Business Combinations. Neither
Pierce Leahy nor Iron Mountain will apply, nor will it take any action resulting
in the application of, or otherwise elect to apply, the provisions of applicable
state takeover laws, if any, with respect to or as a result of the Merger or the
Transactions.   If  any  "fair  price"  or  "control   share   acquisition"   or
"anti-takeover"  statute,  or other similar  statute or regulation  shall become
applicable  to the  transactions  contemplated  hereby,  Pierce  Leahy  and Iron
Mountain and the members of their  respective  Boards of  Directors  shall grant
such approvals and take such actions as are necessary so that the Merger and the
Transactions  may be  consummated  as  promptly  as  practicable  on  the  terms
contemplated  hereby,  and otherwise act to minimize the effects of such statute
or regulation on the Merger and the Transactions.

         Section 5.12. Option Securities.

         (a) Prior to the Effective  Time,  Iron Mountain and Pierce Leahy shall
take such action as may be  necessary to cause each Iron  Mountain  Option to be
automatically  converted in accordance  with Section 2.5. At the Effective Time,
all  references in the stock option  agreements to Iron Mountain shall be deemed
to refer to the Surviving  Corporation.  As of the Effective Time, the Surviving
Corporation shall assume all of Iron Mountain's obligations with respect to Iron
Mountain Options as so amended.

         (b) Without the prior written consent of the other Party, except as set
forth on Section 5.12(b) of the Pierce Leahy Disclosure Schedule,  neither Party
will accelerate, or cause an acceleration of, the exercise,  exchange or vesting
schedule of any of its Option  Securities.  Notwithstanding  the foregoing,  (i)
Pierce Leahy may accelerate the vesting of any Pierce Leahy Options described on
Section  5.12(b)  of the  Pierce  Leahy  Disclosure  Schedule  owned by  current
employees under the Pierce Leahy  Nonqualified  Option Plan, which  acceleration
shall  occur no later  than  immediately  prior to the  Effective  Time and (ii)
Pierce Leahy may accelerate the vesting of any Pierce Leahy Options described on
Section  5.12(b)  of the  Pierce  Leahy  Disclosure  Schedule  owned by  current
non-employee  directors of Pierce Leahy, which acceleration shall occur no later
than immediately prior to the Effective Time.

         Section  5.13.  Tax  Treatment.  Each of Iron Mountain and Pierce Leahy
shall use its  reasonable  best  efforts  to cause the  Merger to  qualify  as a
tax-free  reorganization  under the provisions of Section 368(a) of the Code and
to obtain the opinions of counsel referred to in Sections 6.2(d) and 6.3(c).

         Section    5.14.     Registration    Statement    and    Joint    Proxy
Statement/Prospectus.

         (a) As promptly as practicable after the date of this Agreement, Pierce
Leahy  will  prepare  and  file  with  the  SEC a  registration  statement  (the
"Registration   Statement")  in  connection  with  the  registration  under  the
Securities  Act of the Pierce Leahy  Common  Stock to be issued  pursuant to the
Merger, which Registration Statement shall contain (i) a preliminary joint proxy
statement  to be mailed by Pierce  Leahy and Iron  Mountain to their  respective
shareholders and  stockholders in connection with the vote of such  shareholders
and  stockholders  with  respect to the Merger and the  Transactions  and (ii) a
preliminary  prospectus  of Pierce Leahy in  connection  with such  registration
under the  Securities Act  (together,  the "Joint Proxy  Statement/Prospectus").
Each of Pierce Leahy and Iron Mountain shall use its reasonable  best efforts to
(i) have the Registration Statement declared

<PAGE>

                                       41

effective under the Securities Act as promptly as practicable after such filing,
and (ii) to cause the  Joint  Proxy  Statement/Prospectus  to be mailed to their
respective  shareholders and  stockholders as promptly as practicable  after the
Registration  Statement is declared  effective  under the Securities Act. Pierce
Leahy shall also take any action  (other than  qualifying  to do business in any
jurisdiction  in which it is not now so  qualified or  consenting  to service of
process in any  jurisdiction  in which it has not previously so consented in any
action  other than one arising out of the  offering of the Pierce  Leahy  Common
Stock in such  jurisdiction)  required to be taken to qualify  the Pierce  Leahy
Common Stock to be issued in the Merger under any applicable state securities or
"blue sky" laws prior to the Effective Time, and Iron Mountain shall furnish all
information  concerning Iron Mountain and the Iron Mountain  Stockholders as may
be requested in connection with any such action.

         (b) Pierce Leahy and Iron Mountain shall  cooperate with each other and
provide  to each  other  all  information  necessary  in  order to  prepare  the
Registration  Statement.   Pierce  Leahy  and  Iron  Mountain  shall  use  their
respective  reasonable  best  efforts to respond to any comments of the SEC with
respect to the Registration Statement as promptly as practicable. If at any time
prior to the  Effective  Time there shall occur any Event with respect to Pierce
Leahy or Iron Mountain or any of their respective Subsidiaries,  as the case may
be, or with  respect  to other  information  supplied  by  Pierce  Leahy or Iron
Mountain,  as the case may be, for inclusion in the Registration  Statement,  in
either case which Event is required to be  described  in an  amendment  of, or a
supplement  to,  the  Joint  Proxy   Statement/Prospectus  or  the  Registration
Statement,  Pierce Leahy or Iron Mountain shall notify the other Party, and such
Event shall be so described,  and such amendment or supplement shall be promptly
filed with the SEC and, as  required  by  Applicable  Law,  disseminated  to the
Pierce Leahy Shareholders and the Iron Mountain Stockholders. Pierce Leahy shall
notify  Iron  Mountain  promptly  upon  (i)  the  declaration  by the SEC of the
effectiveness  of the  Registration  Statement,  (ii) the issuance or threatened
issuance of any stop order or other order  preventing or  suspending  the use of
any prospectus relating to the Registration  Statement,  (iii) any suspension or
threatened  suspension of the use of any prospectus relating to the Registration
Statement  in any state,  (iv) any  proceedings  commenced or  threatened  to be
commenced by the SEC or any state securities commission that might result in the
issuance of a stop order or other order or  suspension of use or (v) any request
by the SEC to supplement or amend the Joint Proxy Statement/Prospectus after the
effectiveness  thereof.  Pierce  Leahy  and,  to  the  extent  applicable,  Iron
Mountain,  shall use their reasonable best efforts to prevent or promptly remove
any stop order or other order preventing or suspending the use of any prospectus
relating to the  Registration  Statement  and to comply with any such request by
the  SEC  or  any  state  securities  commission  to  amend  or  supplement  the
Registration Statement or the Joint Proxy Statement/Prospectus.

         (c) Pierce Leahy and Iron Mountain  will notify each other  promptly of
the receipt by such Party or its Representatives of any comments from the SEC or
its staff or any other  appropriate  government  official and of any requests by
the SEC or its staff or any other appropriate government official for amendments
or   supplements   to   the   Registration   Statement   or  the   Joint   Proxy
Statement/Prospectus  or for  additional  information  and will supply the other
Party with copies of all  correspondence  between Pierce Leahy, Iron Mountain or
any of their  respective  Representatives,  on the one hand,  and the SEC or its
staff or any other  appropriate  government  official,  on the other hand,  with
respect thereto.

<PAGE>

                                       42

         (d) None of the information  supplied or to be supplied by Pierce Leahy
or Iron Mountain or any Pierce Leahy  Shareholder  or Iron Mountain  Stockholder
for  inclusion  in  (i)  the  Registration  Statement  will,  at  the  time  the
Registration  Statement  is filed  with the SEC,  at any time it is  amended  or
supplemented  or at the time it  becomes  effective  under the  Securities  Act,
contain any untrue  statement  of a material  fact or omit to state any material
fact required to be stated therein or necessary to make the  statements  therein
not misleading, or (ii) the Joint Proxy  Statement/Prospectus or any other proxy
statement or  information  furnished to the Pierce  Leahy  Shareholders  or Iron
Mountain  Stockholders in connection with the Special Meetings will, at the date
it is first mailed to such  shareholders  or  stockholders or at the time of the
applicable  Special Meeting,  contain any untrue statement of a material fact or
omit to state any material  fact  required to be stated  therein or necessary in
order to make the statements  therein, in light of the circumstances under which
they are made,  not  misleading.  The Joint Proxy  Statement/Prospectus  and the
Registration  Statement will comply as to form in all material respects with the
requirements of the Securities Act.

         Section 5.15.  Exchange Listing.  Pierce Leahy shall use its reasonable
best  efforts to effect,  at or before the  Effective  Time,  authorization  for
listing on the NYSE, upon official  notice of issuance,  of the shares of Pierce
Leahy Common Stock to be issued pursuant to the Merger.

         Section 5.16.  Disclosure  Schedules.  Iron  Mountain  shall deliver to
Pierce Leahy within thirty (30) days after the date of this Agreement,  Sections
4.1(c)  (except  such  sections  otherwise  required  in  Section  4.1(c)  to be
delivered  as of the date of this  Agreement)  and 4.16(c) of the Iron  Mountain
Disclosure  Schedule  and Pierce  Leahy shall  deliver to Iron  Mountain  within
thirty (30) days after the date of this Agreement,  Sections 3.1(c) (except such
sections  otherwise required in Section 3.1(c) to be delivered as of the date of
this  Agreement)  and 3.16(c) of the Pierce Leahy  Disclosure  Schedule.  Pierce
Leahy shall  deliver to Iron  Mountain one (1) business day prior to the Closing
Date an update to Section 3.11(a) of the Pierce Leahy Disclosure Schedule, which
update shall also include the number of Option  Securities  outstanding  (with a
breakdown for each Pierce Leahy Option Plan and an indication of how many Option
Securities are then currently  exercisable) under the Pierce Leahy Option Plans,
as of such date;  provided,  however,  that the only changes to the  information
contained in Section 3.11(a) of the Pierce Leahy Disclosure Schedule between the
date of this  Agreement  and the Closing Date shall be changes  contemplated  or
permitted by this Agreement. Iron Mountain shall deliver to Pierce Leahy one (1)
business day prior to the Closing Date an update to Section  4.11(a) of the Iron
Mountain  Disclosure  Schedule,  which  update  shall also include the number of
Option  Securities  outstanding  (with a breakdown for each Iron Mountain Option
Plan  and an  indication  of how  many  Option  Securities  are  then  currently
exercisable)  under the Iron Mountain Option Plans,  as of such date;  provided,
however,  that the only changes to the information  contained in Section 4.11(a)
of the Iron Mountain  Disclosure Schedule between the date of this Agreement and
the Closing Date shall be changes  contemplated  or permitted by this Agreement.
All other Sections of the Pierce Leahy Disclosure Schedule and the Iron Mountain
Disclosure Schedule shall have been delivered on the date of this Agreement.

         Section 5.17. Pierce Leahy Indebtedness. Pierce Leahy shall assist Iron
Mountain in, and shall take such actions as Iron Mountain may reasonably request
in order to facilitate,  the amendment,  repayment,  redemption,  refinancing or
other restructuring of outstanding  Indebtedness of Pierce Leahy on or after the
Effective Time in connection with the Merger.

<PAGE>


                                       43

         Section  5.18.  Pierce  Leahy  Command  Company.  Prior  to or  at  the
Effective Time,  Pierce Leahy shall cause J. Peter Pierce to transfer his entire
ownership  interests  in PLC Command I, Inc.  and PLC Command II, Inc. to Pierce
Leahy or one of its Subsidiaries for no  consideration,  such that, after giving
effect to such transfer, PLC Command I, L.P. and PLC Command II, L.P. are wholly
owned Subsidiaries of Pierce Leahy.

         Section 5.19. Stock Dividend.  Prior to the Effective Time the Board of
Directors  of Pierce Leahy may declare and pay a stock  dividend on  outstanding
shares of Pierce Leahy Common Stock in an amount equal to one-tenth  (1/10) of a
share of Pierce  Leahy  Common Stock for each share of Pierce Leahy Common Stock
outstanding (the "Stock Dividend").  Pierce Leahy shall convert a holder's right
to receive  shares of Pierce Leahy Common Stock  pursuant to the Stock  Dividend
into a right to  receive  the  highest  whole  number of shares of Pierce  Leahy
Common  Stock  payable with respect to  certificates  representing  Pierce Leahy
Common Stock plus cash in lieu of fractional shares in a reasonable amount based
on the  market  value of  Pierce  Leahy  Common  Stock,  as Pierce  Leahy  shall
determine.  Upon the  effectiveness of the Stock Dividend,  the number of shares
subject to each Pierce  Leahy  Option and the exercise  price  thereof  shall be
proportionately adjusted to give effect to the Stock Dividend.

         Section 5.20. Pierce Leahy Shareholders' Agreement.  Pierce Leahy shall
use its reasonable best efforts to cause each Pierce Leahy Principal Shareholder
who has not  executed the Pierce  Leahy  Shareholders'  Agreement on the date of
this  Agreement to execute and become  party to the Pierce  Leahy  Shareholders'
Agreement on or before  November 3, 1999.  Pierce Leahy shall keep Iron Mountain
informed  of the  results of such  efforts  and shall  deliver to Iron  Mountain
original  counterparts  executed by each Pierce Leahy Principal  Shareholder who
has become party to such Agreement.  In the event Iron Mountain does not receive
original, executed counterparts of the Pierce Leahy Shareholders' Agreement from
all Pierce Leahy  Principal  Shareholders  on or before  November 3, 1999,  Iron
Mountain  shall have the right to terminate  this  Agreement in accordance  with
this Section and Section  7.1(d)(iv) by  delivering  written  notice  thereof to
Pierce Leahy on or before 5:00 p.m. local time on November 8, 1999.

         Section 5.21.  Termination of Plans.  At least one (1) day prior to the
Closing  Date,  Pierce Leahy shall,  at the request of Iron  Mountain,  take all
actions necessary to terminate its participation in any Plan that complies or is
intended to comply with Section 401 of the Code. If such a Plan is terminated in
accordance with this Section 5.21, benefit accruals,  including contributions of
salary reduction  contributions,  if any, shall cease. For a period of three (3)
years  following the Closing Date,  if the Surviving  Corporation  maintains any
Plan intended to comply with Section 401 of the Code,  service with Pierce Leahy
prior to the Closing Date shall, to the extent  permitted by ERISA and the Code,
count  as  service  with  the   Surviving   Corporation   for  purposes  of  the
participation,  vesting and benefit  accrual  provisions of any such Plan to the
extent such  service is  recognized  for  similarly  situated  employees of Iron
Mountain  as of  the  Closing  Date;  provided,  however,  that  there  may be a
reasonable  delay in the effective date of  participation  in any such Plan; and
provided,   further,   that  participation  may  be  limited  by  the  Surviving
Corporation to one such Plan if a similar limitation is imposed by the Surviving
Corporation with respect to Iron Mountain employees as of the Closing Date.


<PAGE>
                                       44


                                   ARTICLE 6.

                               CLOSING CONDITIONS

         Section  6.1.  Conditions  to  Obligations  of Each Party to Effect the
Merger.  The respective  obligations of each Party to effect the Merger shall be
subject to the  satisfaction  at or prior to the Effective Time of the following
conditions,  any or all of which  may be  waived,  in  whole or in part,  to the
extent permitted by Applicable Law:

         (a) This  Agreement,  the Merger and the  Transactions  shall have been
approved and adopted in accordance with the PBCL and the DGCL by the affirmative
vote of the  Pierce  Leahy  Shareholders  and the  Iron  Mountain  Stockholders,
respectively,  holding  at least the  minimum  number of shares of Pierce  Leahy
Common Stock and Iron Mountain  Common  Stock,  as  applicable,  then issued and
outstanding as are required by Applicable Law, Pierce Leahy's Organic  Documents
and Iron  Mountain's  Organic  Documents,  as applicable,  for such approval and
adoption;

         (b) As of the  Closing  Date,  no Legal  Action  shall be pending by or
before  any  Authority  seeking to  restrain,  prohibit,  make  illegal or delay
materially,  or to  impose  any  Adverse  conditions,  or  which  might,  in the
reasonable  business  judgment of Iron Mountain or Pierce Leahy, as the case may
be,  reasonably  be  expected  to  have  an  Adverse  Effect  on  the  Surviving
Corporation and its Subsidiaries  taken as a whole assuming  consummation of the
Merger;

         (c) Other than the filing of the  certificate  of merger in  accordance
with  the DGCL  and  articles  of  merger  in  accordance  with  the  PBCL,  all
authorizations,  consents, waivers, orders or approvals required to be obtained,
and all filings, submissions, registrations, notices or declarations required to
be  made,  by  Iron  Mountain  or  Pierce  Leahy  or  any  of  their  respective
Subsidiaries  prior to the consummation of the Merger and the Transactions shall
have been obtained  from, and made with,  all required  Authorities,  except for
such   authorizations,    consents,   waivers,   orders,   approvals,   filings,
registrations,  notices or declarations the failure to obtain or make would not,
in the  reasonable  judgment of Pierce Leahy or Iron  Mountain,  as  applicable,
assuming  consummation of the Merger,  reasonably be expected to have an Adverse
Effect on the Surviving Corporation;

         (d) The waiting periods (and any extension  thereof)  applicable to the
Merger under the HSR Act shall have expired or been terminated,  and neither the
FTC,  DOJ nor any other  Authority  shall have  authorized  the  institution  of
enforcement  proceedings (that have not been dismissed or otherwise disposed of)
to delay,  prohibit, or otherwise restrain the transactions  contemplated by the
Agreement;

         (e) The shares of Pierce Leahy Common Stock  issuable to Iron  Mountain
Stockholders  pursuant to this Agreement shall have been approved for listing on
the NYSE, subject only to official notice of issuance; and

         (f) The Registration Statement shall have been declared effective,  and
no stop order suspending the  effectiveness of the Registration  Statement shall
be in effect.


<PAGE>

                                       45

         Section  6.2.   Conditions  to  Obligations   of  Iron  Mountain.   The
obligations  of Iron  Mountain  to effect  the  Merger  shall be  subject to the
satisfaction at or prior to the Effective Time of the following conditions,  any
or all of which may be waived,  in whole or in part, to the extent  permitted by
Applicable Law:

         (a) The  representations  and  warranties of Pierce Leahy  contained in
Section 3.11(a) of the Pierce Leahy Disclosure  Schedule (as updated pursuant to
Section  5.16) shall be true and correct in all  material  respects at and as of
the Closing Date with the same force and effect as though made on and as of such
date, and all other  representations and warranties of Pierce Leahy contained in
this  Agreement  or  otherwise  made  in  connection  with  the  Merger  and the
Transactions  shall be true and correct at and as of the  Closing  Date with the
same force and effect as though made on and as of such date  except  those which
speak as of a certain  date which  shall  continue  to be true and correct as of
such  date  on  the  Closing  Date,  except  for  such  failure  of  such  other
representations and warranties to be true and correct as would not reasonably be
expected to have an Adverse Effect on Pierce Leahy or the Surviving Corporation;
each and all of the  covenants  and  conditions  to be performed or satisfied by
Pierce  Leahy  hereunder  at or prior to the  Closing  Date shall have been duly
performed or satisfied  in all  material  respects;  and Pierce Leahy shall have
furnished Iron Mountain with such  certificates  and other documents  evidencing
Pierce Leahy's  compliance with the foregoing  provisions as Iron Mountain shall
have reasonably requested;

         (b) As of the  Closing  Date,  there  shall  not have  occurred  and be
continuing any Adverse Change affecting Pierce Leahy from the condition  thereof
(financial  and other)  reflected  in the most  recent  Pierce  Leahy  Financial
Statements;

         (c) Each of the officers  and  directors of Pierce Leahy (other than J.
Peter  Pierce,  who shall  continue  as the  President  and as a director of the
Surviving Corporation) and each trustee under each Plan shall have submitted his
or her unqualified written  resignation,  dated as of the Closing Date, from all
such positions held with Pierce Leahy and as a trustee for each such Plan;

         (d) Iron Mountain  shall have received a favorable  opinion,  dated the
Closing  Date,  of Sullivan & Worcester  LLP,  its special tax  counsel,  to the
effect that this  Agreement  constitutes  a tax-free plan of  reorganization  in
accordance  with the  provisions  of  Section  368(a)  of the Code and as to the
consequences thereof to the Iron Mountain Stockholders;

         (e) J. Peter Pierce shall have  executed  and  delivered an  employment
agreement  in the  form of  Exhibit  6.2(e)  attached  hereto  (the  "Employment
Agreement");

         (f) The Pierce Leahy Principal  Shareholders eligible to become parties
to the Registration Rights Agreement in accordance with Section 5.6(b)shall have
executed and delivered the Registration Rights Agreement Joinder; and

         (g) All agreements, certificates, opinions and other documents shall be
reasonably  satisfactory  in form,  scope and substance to Iron Mountain and its
counsel,  and Iron Mountain and its counsel shall have received all  information
and copies of all documents,  including records of corporate proceedings,  which
they may  reasonably  request in  connection  therewith,  such  documents  where
appropriate to be certified by proper corporate officers.


<PAGE>


                                       46

         Section 6.3. Conditions to Obligations of Pierce Leahy. The obligations
of Pierce Leahy to effect the Merger shall be subject to the  satisfaction at or
prior to the Effective Time of the following conditions, any or all of which may
be waived, in whole or in part to the extent permitted by Applicable Law:

         (a) The  representations  and warranties of Iron Mountain  contained in
Section 4.11(a) of the Iron Mountain Disclosure Schedule (as updated pursuant to
Section  5.16) shall be true and correct in all  material  respects at and as of
the Closing Date with the same force and effect as though made on and as of such
date, and all other representations and warranties of Iron Mountain contained in
this  Agreement  or  otherwise  made  in  connection  with  the  Merger  and the
Transactions  shall be true and correct at and as of the  Closing  Date with the
same force and effect as though made on and as of such date  except  those which
speak as of a certain  date which  shall  continue  to be true and correct as of
such  date  on  the  Closing  Date,  except  for  such  failure  of  such  other
representations and warranties to be true and correct as would not reasonably be
expected  to  have  an  Adverse   Effect  on  Iron  Mountain  or  the  Surviving
Corporation;  each and all of the  covenants  and  conditions to be performed or
satisfied by Iron Mountain  hereunder at or prior to the Closing Date shall have
been duly  performed or satisfied in all material  respects;  and Iron  Mountain
shall have furnished  Pierce Leahy with such  certificates  and other  documents
evidencing  Iron Mountain's  compliance with the foregoing  provisions as Pierce
Leahy shall have reasonably requested;

         (b) As of the  Closing  Date,  there  shall  not have  occurred  and be
continuing any Adverse Change affecting Iron Mountain from the condition thereof
(financial  and other)  reflected  in the most  recent Iron  Mountain  Financial
Statements;

         (c) Pierce  Leahy shall have  received a favorable  opinion,  dated the
Closing Date, of Cozen and O'Connor, its special tax counsel, to the effect that
this Agreement  constitutes a tax-free plan of reorganization in accordance with
the provisions of Section 368(a) of the Code and as to the consequences  thereof
to Pierce Leahy;

         (d) Iron Mountain  shall have  executed and delivered the  Registration
Rights Agreement Joinder; and

         (e) All agreements, certificates, opinions and other documents shall be
reasonably  satisfactory  in form,  scope and  substance to Pierce Leahy and its
counsel,  and Pierce Leahy and its counsel shall have  received all  information
and copies of all documents,  including records of corporate proceedings,  which
they may  reasonably  request in  connection  therewith,  such  documents  where
appropriate to be certified by proper corporate officers.

                                   ARTICLE 7.

                        TERMINATION, AMENDMENT AND WAIVER

         Section 7.1. Termination.  This Agreement may be terminated at any time
prior to the Effective Time, whether before or after approval of this Agreement,
the Merger and the  Transactions by the Pierce Leahy  Shareholders  and the Iron
Mountain Stockholders as follows:

         (a)      by mutual consent of Iron Mountain and Pierce Leahy;


<PAGE>

                                       47


         (b) by either Iron Mountain or Pierce Leahy:

                  (i) if any permanent injunction,  decree, judgment, statute or
         regulation of or by any Authority  preventing the  consummation  of the
         Merger shall have become final and nonappealable; or

                  (ii) if the Merger and the  Transactions  fail to receive  the
         approval  required by Applicable Law and the Organic  Documents by vote
         of the Pierce Leahy  Shareholders or the Iron Mountain  Stockholders at
         the applicable Special Meeting;

         (c)      by Pierce Leahy:

                  (i) in the event (A) Pierce Leahy is not in material breach of
         any  covenant or  agreement  in this  Agreement,  unless such breach is
         capable of being cured by and will not prevent or delay consummation of
         the Merger by or beyond the  Termination  Date, and (B) either (I) Iron
         Mountain  is in  breach of this  Agreement  or its  representations  or
         warranties  in Section 4.11 shall have become and continue to be untrue
         in any material respect (other than as a result of any action expressly
         permitted by the terms hereof) or any of its other  representations  or
         warranties  shall have become and continue to be untrue and such breach
         or untruth would  reasonably  be expected to have an Adverse  Effect on
         Iron  Mountain  or the  Surviving  Corporation,  unless  such breach or
         untruth  is  capable  of being  cured by and will not  prevent or delay
         consummation of the Merger by or beyond the  Termination  Date, or (II)
         the  Merger  and the  Transactions  have  not been  consummated  by the
         Termination Date;

                  (ii) prior to the approval and adoption of this  Agreement and
         the  Transactions by the Pierce Leahy  Shareholders,  if Pierce Leahy's
         Board of Directors shall withdraw its recommendation of this Agreement,
         the Merger and the Transactions and recommend any Other  Transaction to
         its shareholders;  provided, however, that (i) Pierce Leahy is not then
         in breach of Section  5.7(a),  (ii) prior to such  termination,  Pierce
         Leahy has  negotiated  with Iron  Mountain  in good  faith to make such
         adjustments  in the terms and  conditions  of this  Agreement  as would
         enable  Pierce  Leahy to proceed  with the  Transactions,  (iii) Pierce
         Leahy's Board of Directors  has  determined in good faith (on the basis
         of the terms of such Other Transaction and the terms of this Agreement,
         after  giving  effect  to any  adjustments  offered  by  Iron  Mountain
         pursuant to clause (ii) above),  after consultation with Pierce Leahy's
         outside legal counsel,  that such termination is required for the Board
         of Directors to act in a manner  consistent  with its fiduciary  duties
         under  Applicable  Law and (iv)  Pierce  Leahy  shall  provide  to Iron
         Mountain prior written notice of such termination; or

                  (iii) if (A) the Board of Directors of Iron Mountain shall (I)
         withdraw,  modify or  change  its  recommendation  so that it is not in
         favor of this Agreement, the Merger or the Transactions,  or shall have
         resolved  to do any of the  foregoing,  or  (II)  have  recommended  or
         resolved  to  recommend  to the  Iron  Mountain  Stockholders  any Iron
         Mountain  Transaction,  or (B) Iron Mountain shall have entered into or
         agreed to enter into any Iron Mountain Transaction.


<PAGE>

                                       48

         (d)      by Iron Mountain:

                  (i) in the event (A) Iron  Mountain is not in material  breach
         of any covenant or agreement in this  Agreement,  unless such breach is
         capable of being cured by and will not prevent or delay consummation of
         the Merger by or beyond the Termination Date, and (B) either (I) Pierce
         Leahy is in material breach of this Agreement or its representations or
         warranties  in Section 3.11 shall have become and continue to be untrue
         in any material respect (other than as a result of any action expressly
         permitted by the terms hereof) or any of its other  representations  or
         warranties  shall have become and continue to be untrue and such breach
         or untruth would  reasonably  be expected to have an Adverse  Effect on
         Pierce  Leahy or the  Surviving  Corporation,  unless  such  breach  or
         untruth  is  capable  of being  cured by and will not  prevent or delay
         consummation of the Merger by or beyond the  Termination  Date, or (II)
         the Merger and the Transactions  have not been consummated prior to the
         Termination Date;

                  (ii) prior to the approval and adoption of this  Agreement and
         the Transactions by the Iron Mountain Stockholders,  if Iron Mountain's
         Board of Directors shall withdraw its recommendation of this Agreement,
         the  Merger  and the  Transactions  and  recommend  any  Iron  Mountain
         Transaction  to its  stockholders;  provided,  however,  that  (i) Iron
         Mountain is not then in breach of Section 5.7(b),  (ii) Iron Mountain's
         Board of Directors  has  determined  in good faith (on the basis of the
         terms  of  such  Iron  Mountain  Transaction  and  the  terms  of  this
         Agreement),  after  consultation  with Iron  Mountain's  outside  legal
         counsel,  that such  termination is required for the Board of Directors
         to  act  in  a  manner  consistent  with  its  fiduciary  duties  under
         Applicable  Law and (iii) Iron  Mountain  shall provide to Pierce Leahy
         prior written notice of such termination;

                  (iii) if (A) the Board of  Directors of Pierce Leahy shall (I)
         withdraw,  modify or  change  its  recommendation  so that it is not in
         favor of this Agreement, the Merger or the Transactions,  or shall have
         resolved  to do any of the  foregoing,  or  (II)  have  recommended  or
         resolved  to  recommend  to the  Pierce  Leahy  Shareholders  any Other
         Transaction,  or (B) Pierce  Leahy shall have entered into or agreed to
         enter into any Other Transaction; or

                  (iv) in accordance with Section 5.20 hereof.

         Section 7.2.  Effect of  Termination.  In the event of  termination  by
Pierce  Leahy or Iron  Mountain  pursuant to Section 7.1,  written  notice shall
promptly be given to the other Party hereto and this Agreement  shall  forthwith
become void,  there shall be no  liability  on the part of any Party,  or any of
their  respective  officers  or  directors,  to the  other  and all  rights  and
obligations of any Party shall cease,  except as provided in Sections 5.1, 5.10,
7.2 and 7.5;  provided,  however,  that such  termination  shall not relieve any
Party from liability for the breach of any of its  representations,  warranties,
covenants  or  agreements  set forth in this  Agreement,  or impair the right of
Pierce Leahy,  on the one hand, and Iron Mountain,  on the other hand, to compel
specific performance of the other Party of its obligations under this Agreement.

         Section 7.3. Amendment. This Agreement may be amended by the Parties by
action taken by or on behalf of the  respective  Boards of Directors  thereof at
any time prior to the Effective Time; provided, however, that, after approval of
this Agreement and the Merger by the Pierce Leahy

<PAGE>

                                       49

Shareholders  or the Iron  Mountain  Stockholders,  no  amendment,  which  under
Applicable  Law  may  not  be  made  without  the  approval  of  the  applicable
shareholders or stockholders,  may be made without such approval. This Agreement
may not be amended  except by an  instrument  in writing  signed by the  Parties
hereto.

         Section 7.4. Waiver. At any time prior to the Effective Time, except to
the extent Applicable Law does not permit,  either Iron Mountain or Pierce Leahy
may extend the time for the  performance of any of the obligations or other acts
of the other,  subject,  however,  to the terms and  conditions  of Section 7.1,
waive  any  inaccuracies  in the  representations  and  warranties  of the other
contained  herein  or in  any  document  delivered  pursuant  hereto  and  waive
compliance  by the other with any of the  agreements,  covenants  or  conditions
contained herein.  Any such extension or waiver shall be valid only if set forth
in an agreement in writing signed by the Party or Parties to be bound thereby.

         Section 7.5.      Fees, Expenses and Other Payments.

         (a) All costs and expenses  incurred in connection with this Agreement,
the  Merger  and  the  Transactions,  and  compliance  with  Applicable  Law and
Contractual Obligations as a consequence hereof and thereof, including,  without
limitation,   fees  and  disbursements  of  counsel,   financial   advisors  and
accountants,  incurred by the Parties  shall be borne solely and entirely by the
Party which has incurred such costs and expenses  (except as otherwise  provided
in Section 5.5(e)); provided, however, that all filing fees for all filings made
by Pierce Leahy, Iron Mountain or their respective Affiliates in connection with
the Transactions that are associated with the Registration Statement and the HSR
Act shall be borne one half by each Party.

         (b) In order to induce Iron Mountain to, among other things, enter into
this Agreement,  Pierce Leahy agrees that if this Agreement is terminated (A) by
Iron  Mountain  pursuant  to Section  7.1(d)(iii)  hereof,  (B) by Pierce  Leahy
pursuant to Section  7.1(c)(ii)  hereof, or (C) by Pierce Leahy or Iron Mountain
pursuant to Section  7.1(b)(ii) hereof and (1) Pierce Leahy's Board of Directors
shall have  materially  modified or withdrawn  its  approval,  determination  or
recommendation of this Agreement and the Transactions  prior to the Pierce Leahy
Special Meeting or (2) there shall have been a proposal for an Other Transaction
(an "Other  Proposal") and such proposal shall not have been withdrawn  prior to
the Pierce Leahy Special Meeting and within one (1) year thereafter Pierce Leahy
enters  into  a  definitive  agreement  with  respect  to  such  Other  Proposal
(including any definitive agreement relating to an Other Proposal offered by the
same proponent or its Affiliate as such Other Proposal), then Pierce Leahy shall
promptly pay Iron  Mountain a fee of $35 million.  Any payment  required by this
Section  7.5(b) shall be made in same day funds to Iron Mountain by Pierce Leahy
no later than five (5) business days following  termination of this Agreement by
Pierce Leahy or Iron Mountain, as the case may be, or if applicable, within five
(5) days after execution of such definitive agreement.

         (c) In order to induce Pierce Leahy to, among other things,  enter into
this Agreement, Iron Mountain agrees that if this Agreement is terminated (A) by
Pierce  Leahy  pursuant  to Section  7.1(c)(iii)  hereof,  (B) by Iron  Mountain
pursuant to Section  7.1(d)(ii)  hereof, or (C) by Pierce Leahy or Iron Mountain
pursuant to Section 7.1(b)(ii) hereof and (1) Iron Mountain's Board of Directors
shall have  materially  modified or withdrawn  its  approval,  determination  or
recommendation of this Agreement and the Transactions prior to the Iron Mountain
Special Meeting or (2) there shall have


<PAGE>

                                       50

been a proposal for an Iron Mountain  Transaction (a "Iron  Mountain  Proposal")
and such  proposal  shall not have  been  withdrawn  prior to the Iron  Mountain
Special  Meeting and within one (1) year  thereafter Iron Mountain enters into a
definitive  agreement with respect to such Iron Mountain Proposal (including any
definitive  agreement  relating to an Iron Mountain Proposal offered by the same
proponent or its Affiliate as such Iron Mountain  Proposal),  then Iron Mountain
shall  promptly pay Pierce Leahy a fee of $35 million.  Any payment  required by
this  Section  7.5(c)  shall be made in same day funds to  Pierce  Leahy by Iron
Mountain no later than five (5)  business  days  following  termination  of this
Agreement  by  Iron  Mountain  or  Pierce  Leahy,  as the  case  may  be,  or if
applicable, within five (5) days after execution of such definitive agreement.

         Section  7.6.  Effect  of  Investigation.  The  right  of any  Party to
terminate this Agreement  pursuant to Section 7.1 shall remain  operative and in
full force and effect  regardless of any  investigation  made by or on behalf of
any Party, or any Person  controlling any such party or any of their  respective
Representatives whether prior to or after the execution of this Agreement.

                                   ARTICLE 8.

                               GENERAL PROVISIONS

         Section  8.1.  Nonsurvival  of  Representations  and  Warranties.   All
representations  and warranties in this Agreement shall not survive the Closing,
and after the Effective Time neither Pierce Leahy, Iron Mountain or any of their
respective  Subsidiaries  or  officers  or  directors  shall  have  any  further
obligation with respect thereto.

         Section 8.2.  Notices.  All notices and other  communications  given or
made  pursuant  hereto shall be in writing and shall be deemed to have been duly
given or made as of the date  delivered or  transmitted,  and shall be effective
upon receipt,  if delivered  personally,  mailed by registered or certified mail
(postage  prepaid,  return  receipt  requested)  to the parties at the following
addresses  (or at such other address for a party as shall be specified by giving
written notice) or sent by confirmed  electronic  transmission to the telecopier
number specified below:

         (a)      If to Iron Mountain:

                  745 Atlantic Avenue
                  Boston, MA 02111
                  Attention:  C. Richard Reese
                              Chairman and Chief Executive Officer
                  Telecopier No.:  (617) 535-4734

                  with a copy (which shall not constitute notice) to:

                  Sullivan & Worcester LLP
                  One Post Office Square
                  Boston, MA 02109
                  Attention:  William J. Curry, Esq.
                  Telecopier No.:  (617) 338-2880

<PAGE>

                                       51

         (b)      If to Pierce Leahy:

                  631 Park Avenue
                  King of Prussia, PA  19406
                  Attention:  J. Peter Pierce
                              President and Chief Executive Officer
                  Telecopier No.:  (610) 992-8394

                  with a copy (which shall not constitute notice) to:

                  Cozen and O'Connor
                  1900 Market Street
                  Philadelphia, PA  19103
                  Attention:  Richard J. Busis, Esq.
                  Telecopier No.:  (215) 665-2013

         Section 8.3. Headings. The headings contained in this Agreement are for
purposes  of  reference  only and shall not  affect  in any way the  meaning  or
interpretation of this Agreement.

         Section 8.4.  Severability.  If any term or provision of this Agreement
shall be held or  deemed  to be,  or shall  in fact  be,  invalid,  inoperative,
illegal or  unenforceable  as applied to any particular case in any jurisdiction
or  jurisdictions,  or in all  jurisdictions  or in all  cases,  because  of the
conflict of any  provision  with any  constitution  or statute or rule of public
policy or for any other reason,  such circumstance  shall not have the effect of
rendering the provision or provisions in question invalid, inoperative,  illegal
or unenforceable in any other  jurisdiction or in any other case or circumstance
or of rendering any other  provision or  provisions  herein  contained  invalid,
inoperative,  illegal or  unenforceable to the extent that such other provisions
are not themselves actually in conflict with such constitution,  statute or rule
of public policy, but this Agreement shall be reformed and construed in any such
jurisdiction or case as if such invalid,  inoperative,  illegal or unenforceable
provision had never been contained herein and such provision reformed so that it
would be valid,  operative and  enforceable to the maximum  extent  permitted in
such jurisdiction or in such case.  Notwithstanding the foregoing,  in the event
of any such  determination  the  effect  of which is to  Affect  Materially  and
Adversely either Party, the Parties shall negotiate in good faith to modify this
Agreement  so as to effect  the  original  intent of the  Parties  as closely as
possible to the fullest  extent  permitted by  Applicable  Law in an  acceptable
manner to the end that the  Transactions  are fulfilled and  consummated  to the
maximum extent possible.

         Section  8.5.  Entire  Agreement.  This  Agreement  (together  with the
Confidentiality  Agreement,  the  Pierce  Leahy  Disclosure  Schedule,  the Iron
Mountain  Disclosure  Schedule and the other Collateral  Documents  delivered in
connection  herewith)  constitutes  the  entire  agreement  of the  Parties  and
supersedes all prior agreements and  undertakings,  both written and oral (other
than the Confidentiality  Agreement),  between the Parties, or any of them, with
respect to the subject matter hereof.

         Section 8.6. Assignment. This Agreement shall not be assigned by any of
the Parties hereto (including,  without limitation, by operation of law) and any
purported assignment shall be null and void.

<PAGE>
                                       52


         Section 8.7. Parties in Interest.  This Agreement shall be binding upon
and inure solely to the benefit of each Party (except as specifically  set forth
in Section  5.8(b)),  and,  except for such Section,  nothing in this Agreement,
express or implied,  is  intended to or shall  confer upon any Person any right,
benefit or remedy of any nature whatsoever under or by reason of this Agreement.

         Section 8.8. Governing Law. The validity, interpretation,  construction
and  performance  of this  Agreement  shall be  governed  by, and  construed  in
accordance  with,  the  applicable  laws of the United States of America and the
laws of the State of Delaware applicable to contracts made and performed in such
state and, in any event, without giving effect to any choice or conflict of laws
provision or rule that would cause the application of domestic  substantive laws
of any other jurisdiction,  except to the extent that the provisions of the PBCL
apply to the Merger. Anything in this Agreement to the contrary notwithstanding,
in the event of any dispute between the parties which results in a Legal Action,
the prevailing party shall be entitled to receive from the non-prevailing  party
reimbursement for reasonable legal fees and expenses incurred by such prevailing
party in such Legal Action.

         Section 8.9.  Enforcement of the Agreement.  Each Party  recognizes and
agrees that each other Party's remedy at law for any breach of the provisions of
this  Agreement  would  be  inadequate  and  agrees  that  for  breach  of  such
provisions,  such Party  shall,  in  addition  to such other  remedies as may be
available  to it at law or in  equity  or as  provided  in  this  Agreement,  be
entitled  to  injunctive  relief  and to  enforce  its  rights by an action  for
specific  performance  to the extent  permitted by  Applicable  Law.  Each Party
hereby waives any  requirement  for security or the posting of any bond or other
surety in  connection  with any  temporary  or  permanent  award of  injunctive,
mandatory or other equitable relief. Nothing herein contained shall be construed
as prohibiting a Party from pursuing any other remedies  available to such Party
for any breach or  threatened  breach  hereof or failure to take or refrain from
any action as  required  hereunder  to  consummate  the Merger and carry out the
Transactions.

         Section 8.10.  Counterparts.  This  Agreement may be executed in one or
more counterparts, and by the different Parties hereto in separate counterparts,
each of which when  executed  shall be deemed to be an original but all of which
taken together shall  constitute  one and the same  agreement.  Any signature by
facsimile shall be deemed to be a manual signature for purposes of the execution
of this Agreement.

         Section  8.11.  Mutual  Drafting.  This  Agreement is the result of the
joint efforts of Iron Mountain and Pierce Leahy,  and each provision  hereof has
been  subject to the  mutual  consultation,  negotiation  and  agreement  of the
parties  and there  shall be no  construction  against  any  Party  based on any
presumption of that Party's involvement in the drafting thereof.

                                   ARTICLE 9.

                                   DEFINITIONS

         As used herein,  unless the context otherwise  requires,  the following
terms  (or any  variant  in the  form  thereof)  have the  following  respective
meanings.  Terms  defined in the singular  shall have a comparable  meaning when
used in the plural, and vice versa, and the reference to any gender shall


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                                       53

be deemed to include  all  genders.  Unless  otherwise  defined  or the  context
otherwise clearly  requires,  terms for which meanings are provided herein shall
have such meanings when used in the Pierce Leahy Disclosure  Schedule,  the Iron
Mountain Disclosure Schedule and each Collateral Document, notice,  certificate,
communication,  opinion or other  document  executed  or required to be executed
pursuant hereto or thereto or otherwise  delivered,  from time to time, pursuant
hereto or thereto.

         Adverse,  Adversely, when used alone or in conjunction with other terms
(including without limitation  "Affect," "Change" and "Effect") shall mean, with
respect to Pierce  Leahy or Iron  Mountain,  as the case may be, any Event which
would reasonably be expected to (a) adversely  affect,  in any material respect,
the validity or enforceability  of this Agreement or any Collateral  Document or
the  likelihood  of  consummation  of the  Merger,  (b) to result in a  material
adverse  effect  on the  business,  operations,  management,  properties  or the
condition,  (financial  or other),  or results of operation  (including  without
limitation,  earnings before interest,  taxes, depreciation and amortization) of
Pierce Leahy and its  Subsidiaries  taken as a whole,  or Iron  Mountain and its
Subsidiaries  taken as a whole, as the case may be (it being understood that (i)
a reduction  in the market value of Iron  Mountain  Common Stock or Pierce Leahy
Common Stock shall not, in and of itself,  constitute or be deemed to reflect an
Adverse Change,  (ii) changes in general economic  conditions or in the industry
of Pierce Leahy and Iron Mountain  shall not  constitute or be deemed to reflect
an  Adverse  Change  and  (iii) any  obligation  to  repay,  redeem or  purchase
Indebtedness  of Pierce Leahy in accordance  with the terms thereof as in effect
on the  date  of  this  Agreement  solely  as a  result  of the  Merger  and the
Transactions  shall not  constitute or be deemed to reflect an Adverse  Change),
(c)  materially  impair Pierce Leahy's or Iron  Mountain's,  as the case may be,
ability to fulfill  its  obligations  under the terms of this  Agreement  or any
Collateral Document, or (d) materially adversely affect the aggregate rights and
remedies  of Iron  Mountain  or Pierce  Leahy,  as the case may be,  under  this
Agreement or any Collateral Document.

         Affiliate,  Affiliated shall mean, with respect to any Person,  (a) any
other Person at the time  directly or indirectly  controlling,  controlled by or
under direct or indirect  common control with such Person,  (b) any other Person
of which such Person at the time owns, or has the right to acquire,  directly or
indirectly,  ten percent  (10%) or more of any class of the capital stock (other
than Pierce Leahy Preferred  Stock) or beneficial  interest of such Person,  (c)
any other Person which at the time owns,  or has the right to acquire,  directly
or  indirectly,  ten  percent  (10%) or more of any class of the  capital  stock
(other than Pierce Leahy Preferred Stock) or beneficial interest of such Person,
(d) any  executive  officer or director of such Person,  and (e) with respect to
any partnership, joint venture or similar Entity, any general partner thereof.

         Affiliate  Agreement  shall  have the  meaning  given to it in  Section
5.6(a).

         Agreement shall mean this Agreement as originally in effect,  including
unless the context otherwise  specifically  requires, all schedules and exhibits
hereto, as the same may from time to time be supplemented,  amended, modified or
restated in the manner herein or therein provided.

         Applicable Law shall mean any Law of any Authority, whether domestic or
foreign,  including without limitation the DGCL, the PBCL, all federal and state
securities laws, the Code, ERISA and Environmental Laws, to or by which a Person
or it or any of its business or  operations is subject or any of its property or
assets is bound.


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                                       54

         Authority shall mean any governmental or quasi-governmental  authority,
whether administrative,  executive, judicial or legislative,  whether foreign or
domestic.

         Benefit Arrangement shall mean any material benefit arrangement that is
not a Plan,  including  (i) any  employment or  consulting  agreement,  (ii) any
arrangement providing for insurance coverage or workers' compensation  benefits,
(iii) any incentive  bonus or deferred bonus  arrangement,  (iv) any arrangement
providing termination allowance,  severance, salary continuation for disability,
or  other  leave  of  absence,   supplemental  unemployment  benefits,  lay-off,
reduction in force or similar benefits,  (v) any equity  compensation plan, (vi)
any deferred  compensation  plan,  (vii) any  compensation  policy and practice,
(viii) any educational  assistance  arrangements or policies and (ix) any change
of control arrangements or policies.

         Claims shall mean any and all debts, liabilities,  obligations, losses,
damages,  deficiencies,  assessments  and  penalties,  together  with all  Legal
Actions, pending or threatened in writing, claims and judgments of whatever kind
and nature relating  thereto,  and all fees,  costs,  expenses and disbursements
(including without limitation  reasonable attorneys' and other legal fees, costs
and expenses) relating to any of the foregoing.

         Closing shall have the meaning given to it in Section 1.3.

         Closing Date shall have the meaning given to it in Section 1.3.

         COBRA shall mean the Consolidated Omnibus Budget  Reconciliation Act of
1985, as amended,  as set forth in Section 4980B of the Code and Part 6 of Title
I of ERISA.

         Code  shall  have  the  meaning  given  to it in the  recitals  to this
Agreement.

         Collateral   Documents  shall  mean  the  Pierce  Leahy   Shareholders'
Agreement,  the Iron Mountain Voting Agreement, the Employment Agreement and the
Registration Rights Agreement Joinder.

         Confidentiality Agreement shall have the meaning given to it in Section
5.1(a).

         Contract,  Contractual  Obligation  shall  mean  any  term,  condition,
provision,   representation,   warranty,   agreement,   covenant,   undertaking,
commitment, indemnity or other obligation which is outstanding or existing under
any instrument,  contract,  lease or other contractual  undertaking to which the
obligee is a party or by which it or any of its  business is subject or property
or assets is bound.

         control (including the terms  "controlled,"  "controlled by" and "under
common control with") means the possession, directly or indirectly or as trustee
or executor,  of the power to direct or cause the direction of the management or
policies of a Person,  or the disposition of such Person's assets or properties,
whether through the ownership of stock, equity or other ownership,  by contract,
arrangement or understanding,  or as trustee or executor,  by contract or credit
arrangement or otherwise.

<PAGE>

                                       55

         Convertible Securities shall mean any evidences of indebtedness, shares
of capital stock (other than common stock), equity interests or other securities
directly or indirectly  convertible  into or exchangeable  for shares of capital
stock, equity interests or other securities, whether or not the right to convert
or exchange  thereunder is immediately  exercisable  or is conditioned  upon the
passage of time, the occurrence or  non-occurrence or existence or non-existence
of some other Event, or both.

         DGCL  shall  have  the  meaning  given  to it in the  recitals  to this
Agreement.

         Distribution  shall mean, with respect to Pierce Leahy or Iron Mountain
or any of their respective  Subsidiaries:  (a) the declaration or payment of any
dividend  on or in respect of any shares of any class of capital  stock or other
equity  interests  of Pierce Leahy or Iron  Mountain or any of their  respective
Subsidiaries  owned by a  Person  other  than  Pierce  Leahy  or Iron  Mountain,
respectively,  or  any of  their  respective  Subsidiaries,  (b)  the  purchase,
redemption  or other  retirement  of any shares of any class of capital stock or
other  equity  interest  of  Pierce  Leahy  or  Iron  Mountain  or any of  their
respective  Subsidiaries  owned  by a Person  other  than  Pierce  Leahy or Iron
Mountain,  respectively,  or any of their respective  Subsidiaries,  and (c) any
other  distribution on or in respect of any shares of any class of capital stock
or other  equity  interests  of Pierce  Leahy or Iron  Mountain  or any of their
respective  Subsidiaries  owned  by a Person  other  than  Pierce  Leahy or Iron
Mountain, respectively, or any of their respective Subsidiaries.

         DOJ shall mean the  Department  of Justice of the United  States or any
successor Authority.

         Effective Time shall have the meaning given to it in Section 1.4.

         Employment  Agreement  shall  have the  meaning  given to it in Section
6.2(e).

         Enforceability  Exceptions  shall have the meaning set forth in Section
3.1(b).

         Entity shall mean any corporation,  firm, unincorporated  organization,
association,  partnership,  limited  liability  company,  trust  (inter vivos or
testamentary),  estate of a deceased, insane or incompetent individual, business
trust,  joint stock  company,  joint  venture or other  organization,  entity or
business, whether acting in an individual, fiduciary or other capacity.

         Environmental Law shall mean any Law relating to or otherwise  imposing
liability or  standards of conduct  concerning  pollution or  protection  of the
environment or occupational health and safety, including without limitation Laws
relating to emissions,  discharges, releases or threatened releases of Hazardous
Materials  or  other  pollutants,  contaminants,  chemicals,  noises,  odors  or
industrial,  toxic or  hazardous  substances,  materials  or wastes,  whether as
matter or energy, into the environment (including,  without limitation,  ambient
air,  surface  water,  ground  water,  land  surface  or  subsurface  strata) or
otherwise  relating to the manufacture,  processing,  generation,  distribution,
use, treatment, storage, disposal, cleanup, transport or handling of pollutants,
contaminants,  chemicals or industrial, toxic or hazardous substances, materials
or wastes.

         ERISA shall mean the Employee  Retirement  Income Security Act of 1974,
and the rules and regulations thereunder, all as from time to time in effect, or
any successor law, rules or regulations,


<PAGE>
                                       56

and any reference to any statutory or regulatory provision shall be deemed to be
a reference to any successor statutory or regulatory provision.

         ERISA  Affiliate shall mean any Person that is or has ever been treated
as a single  employer with Pierce Leahy or Iron Mountain,  as applicable,  under
Sections 414(b), (c), (m) or (o) of the Code or Section 4001(b)(1) of ERISA.

         Event  shall  mean the  occurrence  or  existence  of any act,  action,
activity,  circumstance,  condition,  event,  fact,  failure to act, omission or
incident, or any set or combination of any of the foregoing.

         Exchange Act shall mean the  Securities  Exchange Act of 1934,  and the
rules and regulations of the Commission thereunder,  all as from time to time in
effect,  or any successor  law, rules or  regulations,  and any reference to any
statutory  or  regulatory  provision  shall be deemed to be a  reference  to any
successor statutory or regulatory provision.

         Exchange Agent shall have the meaning given to it in Section 2.2(a).

         FTC shall mean the Federal Trade Commission of the United States or any
successor Authority.

         GAAP shall mean generally accepted  accounting  principles as in effect
from time to time in the United States of America.

         Governmental  Authorizations  shall  mean all  approvals,  concessions,
consents,   franchises,   licenses,  permits,  plans,  registrations  and  other
authorizations of all Authorities.

         Governmental  Filings shall mean all filings,  including  franchise and
similar Tax  filings,  and the payment of all fees,  assessments,  interest  and
penalties associated with such filings, with all Authorities.

         Hazardous  Materials  shall mean any  substance  (in whatever  state of
matter):  (a) the presence of which requires  investigation or remediation under
any Environmental  Law; (b) that is defined as a "hazardous  waste",  "hazardous
material" or  "hazardous  substance"  under any  Environmental  Law; (c) that is
toxic, explosive, corrosive, pollutive, contaminating,  infectious, radioactive,
carcinogenic,   mutagenic  or  otherwise  hazardous  and  is  regulated  by  any
Authority;  or (d) that contains or consists of petroleum or petroleum products,
PCBs, asbestos, or urea formaldehyde foam insulation.

         HSR Act shall mean the  Hart-Scott-Rodino  Antitrust Improvement Act of
1976,  and the rules  and  regulations  thereunder,  all as from time to time in
effect,  or any successor  law, rules or  regulations,  and any reference to any
statutory  or  regulatory  provision  shall be deemed to be a  reference  to any
successor statutory or regulatory provision.

         Indebtedness  shall mean,  all  obligations,  contingent  or otherwise,
which in accordance with GAAP should be classified  upon the applicable  Party's
consolidated  balance sheet as  liabilities in respect of borrowed money and all
guarantees, endorsements and other contingent obligations in


<PAGE>
                                       57

respect of  Indebtedness of others (it being  understood  that  obligations of a
Party in  respect of trade  payables  and  capitalized  leases  incurred  in the
ordinary  course  of  business  shall  not  be  included  in the  definition  of
Indebtedness).

         Iron  Mountain  shall have the meaning  given to it in the  recitals to
this Agreement.

         Iron  Mountain/ATSI  Option Plan shall have the meaning  given to it in
Section 4.11(b).

         Iron  Mountain  Common  Stock  shall  have the  meaning  given to it in
Section 2.1(c).

         Iron Mountain  Disclosure  Schedule shall mean the disclosure  schedule
dated as of the date of this  Agreement  delivered  by Iron  Mountain  to Pierce
Leahy; provided, however, that Sections 4.1(c)(to the extent provided in Section
4.1(c) of this Agreement) and 4.16(c) of the Iron Mountain  Disclosure  Schedule
shall be  delivered  by Iron  Mountain to Pierce Leahy no later than thirty (30)
days following the date of this Agreement;  and provided  further,  that Section
4.11(a)  of the Iron  Mountain  Disclosure  Schedule  shall be  updated  one (1)
business day prior to the Closing Date.

         Iron  Mountain  ESPP Plan shall have the meaning given to it in Section
4.11(b).

         Iron Mountain  Financial  Statements shall have the meaning given to it
in Section 4.2(b).

         Iron  Mountain  1995 Option Plan shall have the meaning  given to it in
Section 4.11(b).

         Iron  Mountain  Option  Plans  shall  have the  meaning  given to it in
Section 4.11(b).

         Iron  Mountain  Options  shall have the meaning  given to it in Section
2.5.

         Iron  Mountain  Proposal  shall have the meaning given to it in Section
7.5(c).

         Iron Mountain SEC Reports shall have the meaning given to it in Section
4.2(a).

         Iron  Mountain  Special  Meeting  shall have the meaning given to it in
Section 1.2(b).

         Iron  Mountain  Stockholders  shall have the meaning given to it in the
recitals to this Agreement.

         Iron Mountain Transaction shall mean a transaction or series of related
transactions  (other  than the Merger)  resulting  in any "change in control" of
Iron Mountain (as defined in Iron Mountain's indentures).

         Iron Mountain Voting Agreement shall mean that certain Voting Agreement
of even date herewith  among certain  principal  stockholders  of Iron Mountain,
Pierce  Leahy  and Iron  Mountain,  together  with all  schedules  and  exhibits
thereto, as the same may from time to time be supplemented, amended, modified or
restated in the manner therein provided.

<PAGE>

                                       58

         Iron Mountain's knowledge (including the term "to the knowledge of Iron
Mountain") means the knowledge,  information or belief of C. Richard Reese, John
F. Kenny,  Jr. and John P. Lawrence,  without any duty to investigate or conduct
any inquiry.

         Joint Proxy  Statement/Prospectus shall have the meaning given to it in
Section 5.14(a).

         Law  shall  mean any  administrative,  judicial,  legislative  or other
action, code, consent decree, constitution,  decree, enactment, law, injunction,
judgment,  order,  ordinance,  regulation,   requirement,  rule,  rule  of  law,
settlement agreement, statute or writ of any Authority, domestic or foreign.

         Lease  shall mean any lease of  property,  whether  real,  personal  or
mixed, and all amendments thereto.

         Legal  Action  shall  mean any  litigation  or legal or other  actions,
arbitrations,  counterclaims,  proceedings or suits,  at law or in  arbitration,
equity or  admiralty  commenced  by any Person,  whether or not  purported to be
brought on behalf of a party hereto  affecting such party or any of such party's
business, property or assets.

         Lien shall mean any of the  following:  mortgage;  lien  (statutory  or
other);  or other  security  agreement;  hypothecation,  pledge or other deposit
arrangement;   assignment;   charge;   levy;   executory  seizure;   attachment;
garnishment;   encumbrance   (including  any  easement,   exception,   variance,
reservation or limitation,  right of way,  zoning  restriction,  building or use
restriction,  and the like);  conditional sale, title retention or other similar
agreement,  arrangement,  device or  restriction;  the  filing of any  financing
statement   under  the  Uniform   Commercial  Code  or  comparable  law  of  any
jurisdiction; or restriction on sale, transfer, assignment, disposition or other
alienation (it being understood that any Contractual Obligation which restrains,
limits or impedes the Party or any of its  Subsidiaries  from freely engaging in
any  business or  competing  anywhere  in the world shall not, in any event,  be
considered to be a Lien for purposes of this Agreement).

         Material or  materiality  for the  purposes of this  Agreement,  shall,
unless specifically stated to the contrary,  be determined without regard to the
fact  that  various  provisions  of this  Agreement  set forth  specific  dollar
amounts.

         Material  Agreement shall mean any (i) employment  agreement  requiring
payments of base compensation in excess of $250,000 per year; (ii) joint venture
or similar contract or agreement;  (iii) note,  mortgage,  indenture,  guaranty,
other  obligation,  agreement  or  other  instrument  for  or  relating  to  any
Indebtedness  (including  assumed  Indebtedness)  of  $1,000,000  or more;  (iv)
Contractual  Obligation which  restrains,  limits or impedes the Party or any of
its Subsidiaries  from freely engaging in any business or competing  anywhere in
the world;  or (v) other  Contractual  Obligations  involving an estimated total
future  payment or  payments  by Pierce  Leahy or Iron  Mountain or any of their
respective  Subsidiaries  in excess of $2,000,000  annually or $5,000,000 in the
aggregate (it being understood that leases and customer  contracts shall not, in
any  event,  be  considered  to be  Material  Agreements  for  purposes  of this
Agreement).

         Merger  shall  have the  meaning  given to it in the  recitals  to this
Agreement.


<PAGE>

                                       59

         Multiemployer Plan shall mean a "multiemployer plan" within the meaning
of Section 4001(a)(3) of ERISA.

         NYSE shall  mean the New York Stock  Exchange  or any  successor  stock
exchange or market.

         Option  Securities  shall mean all rights,  options and  warrants,  and
calls or  commitments  evidencing  the right,  to  subscribe  for,  purchase  or
otherwise  acquire  shares of capital  stock,  equity  interests or  Convertible
Securities,  whether or not the right to  subscribe  for,  purchase or otherwise
acquire is immediately  exercisable or is conditioned  upon the passage of time,
the occurrence or non-occurrence or the existence or non-existence of some other
Event.

         Organic  Documents shall mean, with respect to any Party,  the Articles
or Certificate of Incorporation,  by-laws or other organizational  documents and
all   shareholder   or  stockholder   agreements,   voting  trusts  and  similar
arrangements  applicable  to any of its  capital  stock to which such Party is a
party, each as in effect from time to time.

         Other Proposal shall have the meaning given to it in Section 7.5(b).

         Other  Transaction  shall  mean a  transaction  or  series  of  related
transactions  (other than the Merger)  resulting in (a) any change in control of
Pierce Leahy,  (b) any merger or  consolidation  of Pierce Leahy,  regardless of
whether  Pierce Leahy is the surviving  Entity (other than any such  transaction
pursuant to which Pierce Leahy acquires assets or a business so long as (i) such
transaction  is not  prohibited  by  Section  5.2 and (ii)  Pierce  Leahy is the
surviving  corporation),  (c)  any  tender  offer  or  exchange  offer  for  any
securities of Pierce Leahy or any other  acquisition  of greater than 20% of the
Pierce Leahy Common Stock  outstanding,  or (d) any sale or other disposition of
assets of Pierce  Leahy or its  Subsidiaries  if the fair  market  value of such
assets  exceeds 20% of the  aggregate  fair market value of the assets of Pierce
Leahy and its Subsidiaries.

         Party shall mean a signatory to this Agreement.

         PBCL  shall  have  the  meaning  given  to it in the  recitals  to this
Agreement.

         PBGC shall mean the Pension Benefit Guaranty Corporation and any Entity
succeeding to any or all of its functions under ERISA.

         Permitted  Indebtedness  shall mean shares of preferred stock of Pierce
Leahy or additional  Indebtedness of Pierce Leahy (other than  borrowings  under
existing  agreements  as in  effect  on the  date  of  this  Agreement)  that is
redeemable or repayable, as the case may be, at any time at the option of Pierce
Leahy for cash without the payment of any penalty or premium so long as (i) such
preferred  stock  or  Indebtedness  does  not  represent  Option  Securities  or
Convertible  Securities  and  (ii)  the  sum of (A)  the  aggregate  liquidation
preference  and other amounts  required to be paid to redeem such shares and (B)
the aggregate principal amount outstanding or available for borrowing (whichever
is higher) under such Indebtedness does not exceed $50 million.

         Permitted Liens shall mean any of the following Liens: (i) building and
zoning ordinances and by-laws of any applicable  Authority;  (ii) taxes assessed
or to be assessed  for the then  current year to the extent the same are not yet
due or payable; and (iii) rights, easements and restrictions of


<PAGE>
                                       60

record, provided the same do not materially interfere with the current occupancy
and use of any  property  of  Pierce  Leahy  or Iron  Mountain  or any of  their
respective Subsidiaries.

         Person shall mean any natural individual or any Entity.

         Pierce  Leahy  shall have the meaning  given to it in the  introductory
paragraph to this Agreement.

         Pierce Leahy Common Stock shall have the meaning given to it in Section
2.1(a).

         Pierce Leahy  Disclosure  Schedule shall mean the  disclosure  schedule
dated  as of the  date of this  Agreement  delivered  by  Pierce  Leahy  to Iron
Mountain;  provided,  however,  that Sections  3.1(c)(to the extent  provided in
Section  3.1(c) of this  Agreement)  and 3.16(c) of the Pierce Leahy  Disclosure
Schedule  shall be  delivered  by Pierce  Leahy to Iron  Mountain  no later than
thirty (30) days  following the date of this  Agreement;  and provided  further,
that Section  3.11(a) of the Pierce Leahy  Disclosure  Schedule shall be updated
one (1) business day prior to the Closing Date.

         Pierce Leahy Financial Statements shall have the meaning given to it in
Section 3.2(b).

         Pierce  Leahy 1997 Option  Plan shall have the  meaning  given to it in
Section 3.11(b).

         Pierce Leahy  Nonqualified  Option Plan shall have the meaning given to
it in Section 3.11(b).

         Pierce Leahy Option Plans shall have the meaning given to it in Section
3.11(b).

         Pierce Leahy Options shall have the meaning given to it in Section 2.4.

         Pierce  Leahy  Preferred  Stock shall have the  meaning  given to it in
Section 2.1(b).

         Pierce Leahy Principal  Shareholders  shall mean those  shareholders of
Pierce Leahy identified on Section 9 of the Pierce Leahy Disclosure Schedule.

         Pierce Leahy SEC Reports  shall have the meaning given to it in Section
3.2(a).

         Pierce  Leahy  Shareholders  shall have the meaning  given to it in the
recitals to this Agreement.

         Pierce   Leahy   Shareholders'   Agreement   shall  mean  that  certain
Shareholders'  Agreement  of even date  herewith  among all or a portion  of the
Pierce Leahy Principal  Shareholders,  Iron Mountain and Pierce Leahy,  together
with all  schedules and exhibits  thereto,  as the same may from time to time be
supplemented, amended, modified or restated in the manner therein provided.

         Pierce  Leahy  Special  Meeting  shall have the meaning  given to it in
Section 1.2(a).



<PAGE>
                                       61

         Pierce  Leahy's  knowledge  (including  the term "to the  knowledge  of
Pierce  Leahy") means the  knowledge,  information or belief of J. Peter Pierce,
Douglas B. Huntley and Joseph P.  Linaugh,  without any duty to  investigate  or
conduct any inquiry.

         Plan shall mean, at a particular  time, any employee benefit plan which
is covered by ERISA and in respect of which Pierce Leahy or Iron  Mountain,  or,
in the case of any such plan subject to Title IV of ERISA, an ERISA Affiliate is
(or, if such plan were  terminated  at such time,  would under  Section  4069 of
ERISA be deemed to be) an "employer," as defined in Section 3(5) of ERISA, other
than a Multiemployer Plan.

         Private Authorizations shall mean all approvals, concessions, consents,
franchises,  licenses,  permits,  and other authorizations of all Persons (other
than Authorities)  including  without  limitation those with respect to patents,
trademarks, service marks, trade names, copyrights,  computer software programs,
technology and know-how, but not including those with respect to Leases.

         Redeemable  Preferred  Stock  shall  have  the  meaning  given to it in
Section 5.2(viii).

         Registered  Stock shall mean those  shares of Pierce Leahy Common Stock
to be issued in accordance with Section 2.1(c) and to be registered  pursuant to
the Securities Act.

         Registration  Rights  Agreement  shall have the meaning  given to it in
Section 5.6(b).

         Registration  Rights Agreement  Joinder shall have the meaning given to
it in Section 5.6(b).

         Registration Statement shall mean the registration statement (including
the  Joint  Proxy  Statement/Prospectus,   exhibits,  financial  statements  and
schedules   included   therein),   and   all   amendments   thereof   (including
post-effective    amendments)    and    supplements    to   the   Joint    Proxy
Statement/Prospectus  which are a part thereof,  filed under the  Securities Act
registering the Registered Stock.

         Representatives  of  a  Party  shall  mean  the  officers,   directors,
employees,  accountants,  counsel,  financial  advisors,  consultants  and other
representatives of such Party.

         Required Disclosure shall have the meaning given to it in Section 5.10.

         SEC shall mean the  Securities  and Exchange  Commission  of the United
States or any successor Authority.

         Securities Act shall mean the Securities Act of 1933, and the rules and
regulations of the Commission thereunder, all as from time to time in effect, or
any successor law, rules or  regulations,  and any reference to any statutory or
regulatory  provision  shall  be  deemed  to be a  reference  to  any  successor
statutory or regulatory provision.

         Special Meetings shall have the meaning given to it in Section 1.2(b).

         Stock Dividend shall have the meaning given to it in Section 5.19.


<PAGE>

                                       62

         Subsidiary  shall mean, with respect to any Person,  (i) each Entity of
which such Person owns, either directly or indirectly,  50% or more of the stock
or other equity interests, (ii) each partnership in which such Person or another
Subsidiary of such Person is a general  partner or a managing  partner and (iii)
each limited  liability  company in which such Person or another  Subsidiary  of
such Persons is a managing member or otherwise controls.

         Surviving  Corporation  shall have the  meaning  given to it in Section
1.1.

         Tax (and  "Taxable",  which shall mean subject to Tax),  shall mean (a)
all taxes (domestic or foreign),  including without  limitation any income (net,
gross or other  including  recapture  of any tax items  such as  investment  tax
credits),  alternative  or add-on  minimum tax,  gross income,  gross  receipts,
gains,  sales,  use,  leasing,  lease,  user, ad valorem,  transfer,  recording,
franchise,  profits, property (real or personal, tangible or intangible),  fuel,
license,  withholding  on amounts paid to or by Pierce  Leahy or Iron  Mountain,
payroll,  employment,  unemployment,  social security, excise, severance, stamp,
occupation, premium, environmental or windfall profit tax, custom, duty or other
tax, governmental fee or other like assessment or charge of any kind whatsoever,
together with any interest, levies, assessments, charges, penalties, addition to
tax or  additional  amount  imposed  by any Taxing  Authority,  (b) any joint or
several liability of Pierce Leahy or Iron Mountain with any other Person for the
payment of any amounts of the type  described in (a),  and (c) any  liability of
Pierce  Leahy  or Iron  Mountain  for the  payment  of any  amounts  of the type
described in (a) as a result of any express or implied  obligation  to indemnify
any other Person.

         Tax Return or Returns shall mean all returns, consolidated or otherwise
(including without limitation  information  returns),  required to be filed with
any Authority with respect to Taxes.

         Taxing   Authority  shall  mean  any  Authority   responsible  for  the
imposition of any Tax.

         Termination  Date shall  mean April 30,  2000 or such other date as the
Parties may, from time to time, mutually agree.

         Transactions shall mean the transactions contemplated by this Agreement
or the Merger or by any Collateral  Document executed or required to be executed
in connection herewith or therewith, including, without limitation, the election
of directors contemplated by Section 1.8.

         Voting Debt shall have the meaning given to it in Section 3.11(a).

         Year 2000 System shall mean any software  programs,  computer  hardware
and networks,  telephone and voicemail systems and electronically-based  systems
utilized to manage  inventory,  billing,  financial  transactions  or reporting,
facility security, or fire suppression.






                     [Signatures appear on following page.]


<PAGE>


                                       63

         IN WITNESS  WHEREOF,  Iron  Mountain  and Pierce Leahy have caused this
Agreement to be executed as of the date first written above by their  respective
officers thereunto duly authorized.

                                     IRON MOUNTAIN INCORPORATED


                                     By: /s/ C. Richard Reese
                                         Name: C. Richard Reese
                                         Title: Chairman and CEO

                                     PIERCE LEAHY CORP.



                                     By: /s/ J. Peter Pierce
                                        Name: J. Peter Pierce
                                        Title: President and CEO