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                               EXHIBIT 1, SHEET 1
                                Building No. 575
                                TECHNOLOGY SQUARE
                            Cambridge, Massachusetts

                                   LEASE DATA

Execution Date:            September 22, 1999

Tenant:                    AKAMAI TECHNOLOGIES, INC.
                           a Delaware corporation

Mailing Address:           Akamai Technologies, Inc.

                           Prior to the Term Commencement Date in respect of
                           Portion A:
                                    201 Broadway
                                    Cambridge, Massachusetts 02139

                           After the Term Commencement Date in respect of
                           Portion A:
                                    575 Technology Square
                                    Cambridge, Massachusetts 02139-3539

Landlord:                  TECHNOLOGY SQUARE LLC, a Delaware limited liability
                           company (the sole manager of which is Beacon Capital
                           Partners L.P., a Delaware limited partnership d/b/a
                           Beacon Capital Partners Limited Partnership; the sole
                           general partner of which is Beacon Capital Partners,
                           Inc., a Maryland corporation)

Mailing Address:           c/o Beacon Capital Partners, One Federal Street,
                           Boston, Massachusetts 02110, Attention: General
                           Counsel

Complex:                   The land, buildings and other improvements thereon,
                           from time to time, located off Main Street in the
                           City of Cambridge, Middlesex County, Commonwealth of
                           Massachusetts known as Technology Square. The Complex
                           is initially substantially as shown on Exhibit 6,
                           Sheet 1, and the legal description of the Complex is
                           set forth on Exhibit 6, Sheets 2, 3, and 4; however,
                           the Complex may change from time to time as set forth
                           herein.

Building:                  575 Technology Square, Cambridge, Massachusetts

Premises:                  The entirety of the second (2nd), third (3rd), fourth
                           (4th), fifth (5th), sixth (6th) and seventh (7th)
                           floors of the Building, substantially as shown on
                           Lease Plan, Exhibit 2, Sheets 1, 2, 3, 4, 5 and 6.
                           The portion of the Premises on the third (3rd),
                           fourth (4th), fifth (5th), and sixth (6th)floors are
                           hereinafter referred to as "Portion "A" of the
                           Premises. The second (2nd) and seventh (7th) floors
                           of the
<PAGE>   2
                               EXHIBIT 1, SHEET 2
                                Building No. 575
                                TECHNOLOGY SQUARE
                            Cambridge, Massachusetts

                       Tenant: Akamai Technologies, Inc.
                      Execution Date: September 22, 1999

                           Premises are hereinafter referred to as "Portion B"
                           of the Premises and each of Portion A and Portion B
                           is hereinafter referred to as a "Portion" of the
                           Premises.

Art. 3.1                   Specified Commencement Date in respect of:
                                    Portion A:  January 18, 2000
                                    Portion B:  June 1, 2000

Art. 3.2                   Termination Date:   Seven (7) years after the Term
                                               Commencement Date in respect
                                               of Portion A

Art. 4                     Final Plans Date in respect of:
                                    Portion A:  October 18, 1999
                                    Portion B:  December 1, 1999

Art. 5                     Use of Premises: General business office use


Art. 6                     Yearly Rent in respect of:

                           Portion A:
<TABLE>
<CAPTION>
                           Lease Year                Yearly Rent            Monthly Payment
                           ----------                -----------            ---------------
<S>                                               <C>                       <C>
                               1 - 2:(1)          $2,677,200.00(2)          $223,100.00(2)

                           Lease Years 3 - 4:     $2,784,288.00             $232,024.00

                           Lease Years 5 - 7:     $2,927,072.00             $243,922.67
</TABLE>

                           Portion B:
<TABLE>
<CAPTION>

                           Time Period              Yearly Rent             Monthly Payment
                           -----------              -----------             ---------------
<S>                                                <C>                     <C>
</TABLE>

--------

(1) For the purposes of this Lease, "Lease Year 1" shall be defined as the
twelve-(12)-month period commencing as of the Term Commencement Date in respect
of Portion A and ending on the last day of the month in which the first (1st)
anniversary of the Term Commencement Date in respect of Portion A occurs.
Thereafter, "Lease Year" shall be defined as any twelve (12) month period during
the term of the Lease commencing as of the first (1st) day of the month
following the month in which any anniversary of the Term Commencement Date
occurs.

(2) Subject to Article 6(a).



                                      -2-
<PAGE>   3
                               EXHIBIT 1, SHEET 3
                                Building No. 575
                                TECHNOLOGY SQUARE
                            Cambridge, Massachusetts

                       Tenant: Akamai Technologies, Inc.
                      Execution Date: September 22, 1999

<TABLE>

<S>                        <C>                      <C>               <C>
                           Term Commencement
                           Date in respect of
                           Portion B -
                           end of Lease Year 2:     $1,383,220.00     $115,268.33

                           Lease Years 3 - 4:       $1,409,992.00     $117,499.33

                           Lease Years 5 - 7:       $1,499,232.00     $124,936.00
</TABLE>

Art. 7                     Total Rentable Area of the Premises:
<TABLE>

<S>                                                                     <C>
                                     Portion A:                          71,392 square feet
                                                                         (i.e., 17,848 square
                                                                         feet for each of the,
                                                                         third (3rd), fourth
                                                                         (4th), fifth (5th) and
                                                                         sixth (6th) floors)

                                     Portion B:                          35,696 square feet
                                                                         (i.e., 17,848 square
                                                                         feet for each of the
                                                                         second (2nd) and
                                                                         seventh (7th) floors)

                           Total Rentable Area of the Building:          182,259 square feet

                           Initial Total Rentable Area of the Complex:   540,954 square feet
</TABLE>


Art. 8                     Electricity:     Electric current will be metered and
                                            paid for by Tenant in accordance
                                            with Article 8.1 of the Lease.

Art. 9                     Operating and Tax Escalation:

                           Operating Expense Excess:

           Tenant's Building Operating Cost Percentage in respect of:
                               Portion A:  39.17%(2)
                               Portion B:  19.59%

                               Note:   Tenant's Building Operating Cost
                                       Percentage is a ratio of the Total
                                       Rentable


                                      -3-
<PAGE>   4
                               EXHIBIT 1, SHEET 4
                                Building No. 575
                                TECHNOLOGY SQUARE
                            Cambridge, Massachusetts

                       Tenant: Akamai Technologies, Inc.
                      Execution Date: September 22, 1999


                                       Area of the Portion of the Premises to
                                       the Total Rentable Area of the Building,
                                       and will change if the Total Rentable
                                       Area of the Building changes.

            Tenant's Complex Operating Cost Percentage in respect of:
                               Portion A: 13.20%(2)
                               Portion B:  6.60%

                               Note:   Tenant's Complex Operating Cost
                                       Percentage is a ratio of the Total
                                       Rentable Area of the Portion of the
                                       Premises to the Total Rentable Area of
                                       the Complex, and will change if the Total
                                       Rentable Area of the Complex changes.

                               Building Operating Costs Base:  The actual amount
                                        of Building Operating Costs for calendar
                                        year 2000, adjusted pursuant to Article
                                        9.6

                               Complex Operating Costs Base:  Complex Operating
                                   Costs for calendar year 2000, adjusted
                                   pursuant to Article 9.6

                               Tax Excess:

                               Tenant's Building Tax Percentage in respect of:
                                            Portion A:  39.17%(2)
                                            Portion B:  19.59%

                                            Note:    Tenant's Building Tax
                                                     Percentage is a ratio of
                                                     the Total Rentable Area of
                                                     the Portion of the Premises
                                                     to the Total Rentable Area
                                                     of the Building, and will
                                                     change if the Total
                                                     Rentable Area of the
                                                     Building changes.

                                Building Tax Base:     The arithmetic average of
                                                       the actual amount of
                                                       Building Taxes for fiscal
                                                       tax year 2000 (i.e., July
                                                       1, 1999 - June 30, 2000)
                                                       and fiscal tax year



                                      -4-
<PAGE>   5
                               EXHIBIT 1, SHEET 5
                                Building No. 575
                                TECHNOLOGY SQUARE
                            Cambridge, Massachusetts

                       Tenant: Akamai Technologies, Inc.
                      Execution Date: September 22, 1999


                                                       2001 (i.e., July 1,
                                                       2000-June 30, 2001)

                                 Tenant's Complex Tax Percentage in respect of:
                                         Portion A:   13.20%(2)
                                         Portion B:    6.60%

                                            Note:    Tenant's Complex Tax
                                                     Percentage is a ratio of
                                                     the Total Rentable Area of
                                                     the Portion of the Premises
                                                     to the Total Rentable Area
                                                     of the Complex, and will
                                                     change if the Total
                                                     Rentable Area of the
                                                     Complex changes.

                                    Complex Tax Base:  The arithmetic average of
                                                       the actual amount of Land
                                                       Taxes for fiscal tax year
                                                       2000 (i.e., July 1, 1999
                                                       - June 30, 2000) and
                                                       fiscal year 2001 (i.e.,
                                                       July 1, 2000-June 30,
                                                       2001)

Art. 29.3                  Co-Brokers:      Insignia/ESG and Spaulding & Slye

Art. 29.5                  Arbitration:     Superior Court; Middlesex County

                           Exhibit Date:    Lease Plan, Exhibit 2, Sheets 1, 2,
                                            3, 4, 5 and 6 dated August 16, 1999

                                      -5-
<PAGE>   6
                               EXHIBIT 1, SHEET 6
                                Building No. 575
                                TECHNOLOGY SQUARE
                            Cambridge, Massachusetts

                       Tenant: Akamai Technologies, Inc.
                      Execution Date: September 22, 1999


LANDLORD:                                                     TENANT:

TECHNOLOGY SQUARE LLC,                            AKAMAI TECHNOLOGIES, INC.
a Delaware limited liability company              a Delaware corporation

By: Beacon Capital Partners L.P.,
    a Delaware limited partnership
    d/b/a Beacon Capital Partners
    Limited Partnership, its manager

    By: Beacon Capital Partners, Inc., a
        Maryland corporation, its general
        partner

        By: _______________________               By: _______________________
        Name: Thomas Ragno                        Name: _____________________
        Title: Senior Vice President              Title: ______________________

Date Signed: _______________________              Date Signed: ________________


                                      -6-
<PAGE>   7
                                    CONTENTS
<TABLE>
<S>                                                                        <C>
1.       REFERENCE DATA..................................................    1

2.       DESCRIPTION OF PREMISES.........................................    1
         2.1      Demised Premises.......................................    1
         2.2      Appurtenant Rights.....................................    1
         2.3      Parking................................................    1
         2.4      Exclusions and Reservations............................    1

3.       TERM OF LEASE...................................................    1
         3.1      Definitions............................................    1
         3.2      Habendum...............................................    2
         3.3      Declaration Fixing Term Commencement Date..............    2

4.       READINESS FOR OCCUPANCY - ENTRY BY TENANT
         PRIOR TO TERM COMMENCEMENT DATE.................................    2
         4.1      Completion Date - Delays...............................    2
         4.2      When Premises Deemed Ready.............................    2
         4.3      Plans and Specifications...............................    3
         4.4      Preparation of Premises................................    3
         4.5      Intentionally Omitted..................................    4
         4.6      Tenant's Delay - Additional Costs......................    4
         4.7      Entry by Tenant Prior to Term Commencement Date........    4
         4.8      Conclusiveness of Landlord's Performance...............    4
         4.9      Tenant Payments of Construction Cost...................    4

5.       USE OF PREMISES.................................................    5
         5.1      Permitted Use..........................................    5
         5.2      Prohibited Uses........................................    5
         5.3      Licenses and Permits...................................    5

6.       RENT     .......................................................    5

7.       RENTABLE AREA - ADJUSTMENT OF RENT..............................    6

8.       SERVICES FURNISHED BY LANDLORD..................................    6
         8.1      Electric Current.......................................    8
         8.2      Water..................................................    8
         8.3      Elevators, Heat, Cleaning..............................    8
         8.4      Air Conditioning.......................................    8
         8.5      Additional Heat, Cleaning and
                  Air Conditioning Services..............................    9
         8.6      Additional Air Conditioning Equipment..................    9
         8.7      Repairs................................................    9
         8.8      Interruption or Curtailment of Services................    9
         8.9      Energy Conservation....................................    9
         8.10     Miscellaneous..........................................   10

9.       ESCALATION......................................................   10
         9.1      Definitions............................................   10
         9.2      Tax Excess.............................................   12
</TABLE>
                                      -i-
<PAGE>   8
<TABLE>
<S>                                                                        <C>
         9.3      Operating Expense Excess...............................   12
         9.4      Part Years.............................................   13
         9.5      Effect of Taking.......................................   13
         9.6      Adjustment of Operating Costs based upon Occupancy.....   13
         9.7      Survival...............................................   13

10.      CHANGES OR ALTERATIONS BY LANDLORD..............................   13

11.      FIXTURES, EQUIPMENT AND IMPROVEMENTS - REMOVAL BY TENANT........   14

12.      ALTERATIONS AND IMPROVEMENTS BY TENANT..........................   14

13.      TENANT'S CONTRACTORS - MECHANIC'S AND OTHER LIENS -
         STANDARD OF TENANT'S PERFORMANCE - COMPLIANCE WITH LAWS.........   15

14.      REPAIRS BY TENANT - FLOOR LOAD..................................   15
         14.1     Repairs by Tenant......................................   15
         14.2     Floor Load - Heavy Machinery...........................   16

15.      INSURANCE, INDEMNIFICATION, EXONERATION AND EXCULPATION.........   16
         15.1     General Liability Insurance............................   16
         15.2     Certificates of Insurance..............................   16
         15.3     General................................................   17
         15.4     Property of Tenant.....................................   17
         15.5     Bursting of Pipes, etc.................................   17
         15.6     Repairs and Alterations - No Diminution ...............   18
                  of Rental Value

16.      ASSIGNMENT, MORTGAGING AND SUBLETTING...........................   18

17.      MISCELLANEOUS COVENANTS.........................................   19
         17.1     Rules and Regulations..................................   19
         17.2     Access to Premises - Shoring...........................   19
         17.3     Accidents to Sanitary and Other Systems................   20
         17.4     Signs, Blinds and Drapes...............................   20
         17.5     Estoppel Certificate...................................   20
         17.6     Prohibited Materials and Property......................   21
         17.7     Requirements of Law - Fines and Penalties..............   21
         17.8     Tenant's Acts - Effect on Insurance....................   21
         17.9     Miscellaneous..........................................   22

18.      DAMAGE BY FIRE, ETC.............................................   22

19.      WAIVER OF SUBROGATION...........................................   23

20.      CONDEMNATION - EMINENT DOMAIN...................................   24

21.      DEFAULT ........................................................   24
         21.1     Conditions of Limitation - Re-entry - Termination......   24
         21.2     Damages - Assignment for Benefit of Creditors..........   25
         21.3     Damages - Termination..................................   26
         21.4     Fees and Expenses......................................   27
         21.5     Waiver of Redemption...................................   27
</TABLE>

                                      -ii-
<PAGE>   9
<TABLE>
<S>                                                                        <C>
         21.6     Landlord's Remedies Not Exclusive......................   27
         21.7     Grace Period...........................................   27

22.      END OF TERM - ABANDONED PROPERTY................................   28

23.      SUBORDINATION...................................................   29

24.      QUIET ENJOYMENT.................................................   30

25.      ENTIRE AGREEMENT  - WAIVER - SURRENDER..........................   31
         25.1     Entire Agreement.......................................   31
         25.2     Waiver.................................................   31
         25.3     Surrender..............................................   31

26.      INABILITY TO PERFORM - EXCULPATORY CLAUSE.......................   31

27.      BILLS AND NOTICES...............................................   32

28.      PARTIES BOUND - SEIZING OF TITLE................................   33

29.      MISCELLANEOUS...................................................   33
         29.1     Separability...........................................   33
         29.2     Captions, etc..........................................   33
         29.3     Broker.................................................   33
         29.4     Modifications..........................................   33
         29.5     Arbitration............................................   34
         29.6     Governing Law..........................................   34
         29.7     Assignment of Rents....................................   34
         29.8     Representation of Authority............................   34
         29.9     Expenses Incurred by Landlord Upon Tenant Requests.....   34
         29.10    Survival...............................................   34

EXHIBITS

         Exhibit 1 Lease Data............................................
         Exhibit 2 Lease Plans...........................................
         Exhibit 3 Building Standard Items...............................   36
         Exhibit 4 Building Services.....................................   40
         Exhibit 5 Form of Letter of Credit..............................   40
         Exhibit 6 Base Building Work....................................
         Exhibit 7 Exterior Sign.........................................
         Exhibit 8 Tenant's Removable Property
</TABLE>

                                     -iii-
<PAGE>   10
         THIS INDENTURE OF LEASE made and entered into on the Execution Date as
stated in Exhibit 1 and between the Landlord and the Tenant named in Exhibit 1.

Landlord does hereby demise and lease to Tenant, and Tenant does hereby hire and
take from Landlord, the Premises hereinafter mentioned and described
(hereinafter referred to as "Premises"), upon and subject to the covenants,
agreements, terms, provisions and conditions of this Lease for the term
hereinafter stated:

1.       REFERENCE DATA

         Each reference in this Lease to any of the terms and titles contained
in any Exhibit attached to this Lease shall be deemed and construed to
incorporate the data stated under that term or title in such Exhibit.

2.       DESCRIPTION OF DEMISED PREMISES

         2.1.  DEMISED PREMISES. The Premises are that portion of the
Building as described in Exhibit 1 and is hereinafter referred to as "Building",
substantially as shown hatched or outlined on the Lease Plan (Exhibit 2) hereto
attached and incorporated by reference as a part hereof.

         2.2.  APPURTENANT RIGHTS. Tenant shall have, as appurtenant to the
Premises, rights to use in common, with others entitled thereto, subject to
reasonable rules from time to time made by Landlord of which Tenant is given
notice; (a) the common lobbies, hallways, stairways and elevators of the
Building, serving the Premises in common with others, (b) common walkways
necessary for access to the Building, and (c) if the Premises include less than
the entire rentable area of any floor, the common toilets and other common
facilities of such floor; and no other appurtenant rights or easements. Landlord
shall allow Tenant's telecommunication service provider to have access to the
Building and to Tenant's Premises, provided however, that Landlord shall have
the right to charge Tenant's provider fees in connection with the services being
performed by such provider.

         2.3.  PARKING. During the term of the Lease, the Landlord will make
available, at Tenant's written request, which request must be made on or before
the Term Commencement Date in respect of Portion A, up to one and one-half (1.5)
monthly parking passes per 1,000 square feet of Total Rentable Area leased by
Tenant (the "Parking Space Cap") for use in the garage of the Complex or surface
parking areas in the Building, as the same may change from time to time
("Parking Areas"). If Tenant fails timely to make such request for any such
parking passes, Tenant shall have no right to obtain such parking passes under
this Article 2.3, except to the extent thereafter available, as more
specifically set forth herein. If Tenant requests fewer passes than the Parking
Space Cap prior to the Term Commencement Date, Tenant shall have the right, from
time to time during the term of the Lease, to request additional parking passes
up to the Parking Space Cap. If Landlord has such passes available, Landlord
will provide the same to Tenant (but in no event more than the Parking Space
Cap), provided however, that, if such passes are not available, Landlord shall
have no obligation to provide additional passes to Tenant. Tenant shall have no
right to sublet, assign, or otherwise transfer said parking passes, other than
to an Assignee or a Qualified Transferee pursuant to an approved assignment or
sublease under Article 16 of the Lease. Said parking passes shall be paid for by
Tenant at the then current prevailing rate in the Parking Areas, as such rate
may vary from time to time. If, for any reason, Tenant shall fail timely to pay
the charge for said parking passes, and if such default continues for ten (10)
days after written notice, Tenant shall have no further right to the parking
passes for which Tenant failed to pay the charge under this Article 2.3. Said
parking passes will be on an unassigned, non-reserved basis, and shall be
subject to such reasonable and uniform rules and regulations as may be in effect
for the use of said Parking Areas, from time to time in force.

                                      -1-
<PAGE>   11
         2.4. EXCLUSIONS AND RESERVATIONS. All the perimeter walls of the
Premises except the inner surfaces thereof, any balconies (except to the extent
same are shown as part of the Premises on the Lease Plan (Exhibit 2)), terraces
or roofs adjacent to the Premises, and any space in or adjacent to the Premises
used for shafts, stacks, pipes, conduits, wires and appurtenant fixtures, fan
rooms, ducts, electric or other utilities, sinks or other Building facilities,
and the use thereof, as well as the right of access through the Premises for the
purposes of operation, maintenance, decoration and repair, are expressly
excluded from the Premises and reserved to Landlord.

3.       TERM OF LEASE

         3.1.  DEFINITIONS. As used in this Lease the words and terms which
follow mean and include the following:

               (a) "Specified Commencement Date" - The date (as stated in
Exhibit 1) on which it is estimated that the Portion of the Premises in question
will be ready for Tenant's occupancy for its use as stated in Exhibit 1.

               (b) "Term Commencement Date" - The "Term Commencement Date"
with respect to Portion A is the date nine (9) days before the date on which
Portion A of the Premises is ready for Tenant's occupancy (as defined in Article
4.2) for use as set forth in Exhibit 1, but in no event prior to January 1,
2000. The "Term Commencement Date" with respect to Portion B is the date on
which Portion B of the Premises is ready for Tenant's occupancy (as defined in
Article 4.2) for use as set forth in Exhibit 1. If such Portion of the Premises
is not ready for such occupancy but if, pursuant to permission therefor duly
given by Landlord, Tenant takes possession of the whole or any part of such
Portion of the Premises for use as set forth in Exhibit 1, "Term Commencement
Date" for such Portion shall be the date on which Tenant takes such possession.

         3.2.  HABENDUM. TO HAVE AND TO HOLD each Portion of the Premises for
a term of years commencing on the Term Commencement Date in respect of such
Portion and ending on the Termination Date as stated in Exhibit 1 or on such
earlier date upon which said term may expire or be terminated pursuant to any of
the conditions of limitation or other provisions of this Lease or pursuant to
law (which date for the termination of the terms hereof will hereafter be called
"Termination Date"). Notwithstanding the foregoing, if the Termination Date as
stated in Exhibit 1 shall fall on other than the last day of a calendar month,
said Termination Date shall be deemed to be the last day of the calendar month
in which said Termination Date occurs.

         3.3.  DECLARATION FIXING TERM COMMENCEMENT DATE. As soon as may be
after the execution date hereof, each of the parties hereto agrees, upon demand
of the other party to join in the execution, in recordable form, of a statutory
notice, memorandum, etc. of lease and/or written declaration in which shall be
stated each such Term Commencement Date and (if need be) the Termination Date.
If this Lease is terminated before the term expires, then upon Landlord's
request the parties shall execute, deliver and record an instrument
acknowledging such fact and the date of termination of this Lease, and Tenant
hereby appoints Landlord its attorney-in-fact in its name and behalf to execute
such instrument if Tenant shall fail to execute and deliver such instrument
after Landlord's request therefor within ten (10) days.

4.       READINESS FOR OCCUPANCY - ENTRY BY TENANT PRIOR TO TERM COMMENCEMENT
         DATE

         4.1  COMPLETION DATE - DELAYS.

         (a) Subject to delay by causes set forth in Article 26 ("Force Majeure
Delays") or caused by a Tenant Delay, as hereinafter defined, Landlord shall use
reasonable speed and diligence to have each

                                      -2-
<PAGE>   12
Portion of the Premises ready for Tenant's occupancy on its respective Specified
Commencement Date. The failure to have such Portion of the Premises ready for
Tenant's occupancy on the Specified Commencement Date in respect of such Portion
shall in no way affect the validity of this Lease or the obligations of Tenant
hereunder nor shall the same be construed in any way to extend the term of this
Lease. If a Portion of the Premises is not ready for Tenant's occupancy within
the meaning of Article 4.2 hereof on the Specified Commencement Date for such
Portion, Tenant shall not have any claim against Landlord, and Landlord shall
have no liability to Tenant, by reason thereof. In addition, Landlord shall use
reasonable efforts to have the lockers and showers shown on Plan A5-1, Enlarged
Basement Core Plan, dated May 10, 1999, as modified by Plan SKA031 dated August
31, 1999, both prepared by Sasaki Associates in association with DTS Shaw, Inc.,
completed, at Landlord's expense, by the Specified Commencement Date in respect
of Portion A, but Landlord's failure so to do shall not affect the Term
Commencement Date in respect of Portion A.

         (b) Notwithstanding anything to the contrary herein contained, if the
Term Commencement Date in respect of either Portion of the Premises has not
occurred on or before the date ("Initial Target Date") sixty (60) days after the
Specified Commencement Date in respect of such Portion, then Tenant shall be
entitled to a credit against the Yearly Rent otherwise payable in respect of
such Portion from and after the Term Commencement Date in respect of such
Portion equal to the amount of Yearly Rent payable in respect of such Portion
for one (1) day for each day between the Initial Target Date and the Term
Commencement Date in respect of such Portion, provided however, that the Initial
Target Date shall be extended by the number of days that Landlord's Work in
respect of such Portion is delayed due to Force Majeure Delays.

         (c) Notwithstanding the foregoing, if the Term Commencement Date in
respect of Portion A shall not have occurred on or before the Outside Target
Date, as hereinafter defined, then Tenant shall have the right, exercisable by a
written thirty (30) day termination notice given on or after the Outside Target
Date, to terminate the Lease. If the Term Commencement Date in respect of
Portion A occurs on or before the thirtieth (30th) day after Landlord receives
such termination notice, Tenant's termination notice shall be deemed to be void
and of no force or effect. If the Term Commencement Date in respect of Portion A
does not occur on or before such thirtieth (30th) day, this Lease shall
terminate and shall be of no further force or effect. For the purposes hereof,
the "Outside Target Date" shall be defined as the date ninety (90) days after
the Specified Commencement Date in respect of Portion A, provided however, that
the Outside Target Date shall be extended by the lesser of (i) the length of any
delays in Landlord's Work in respect of Portion A arising from Force Majeure
Delays, and (ii) ninety (90) days.

         4.2      WHEN PREMISES DEEMED READY.

         (a) Definition of Substantially Completed. Each Portion of the Premises
shall be conclusively deemed ready for Tenant's occupancy as soon as (i)
Landlord's Work, as hereinafter defined, in such Portion has been substantially
completed by Landlord insofar as is practicable in view of Tenant Delays and the
elevator, plumbing, air conditioning and electric facilities are substantially
available to Tenant, and in good working order, in accordance with the
obligations assumed by Landlord hereunder and (ii) the City of Cambridge shall
have issued a permanent, unconditional certificate of occupancy, or its
equivalent, permitting Tenant to legally occupy such Portion of the Premises.
Landlord's Work shall be defined as the work to be performed by Landlord in
preparing each Portion of the Premises for Tenant's occupancy as shown on
Tenant's final approved plans in respect of such Portion of the Premises,
provided however, that if Landlord's Work in respect of any Portion of the
Premises is delayed as the result of any Tenant Delays, then such Portion shall
be deemed to be ready for Tenant's occupancy as of date that such Portion would
have been substantially completed but for such Tenant Delays. Notwithstanding
the foregoing, if Tenant engages its own contractors to perform any portion of
the work to be performed in the initial preparation of such Portion of the
Premises, Landlord shall be relieved of its responsibility for obtaining such
certificate of occupancy to the extent that Landlord's failure to obtain such
certificate of occupancy is based upon any aspect of the work performed by
Tenant's contractors. A

                                      -3-
<PAGE>   13
Portion of the Premises shall not be deemed to be unready for Tenant's occupancy
or incomplete if only minor or insubstantial details of construction, decoration
or mechanical adjustments remain to be done in such Portion of the Premises or
any part thereof which will not materially interfere with Tenant's conduct of
business in such Portion of the Premises. If a Portion of the Premises is deemed
ready for Tenant's occupancy, pursuant to the foregoing, (and the term shall
have commenced by reason thereof), but such Portion of the Premises is not in
fact actually ready for Tenant's occupancy, Tenant shall not (except with
Landlord's consent) be entitled to take possession of such Portion of the
Premises for use as set forth in Exhibit 1 until such Portion of the Premises is
in fact actually ready for such occupancy. Landlord's architect's certificate of
substantial completion, as hereinabove stated, given in good faith, or of any
other facts pertinent to this Article 4.2 shall be deemed conclusive of the
statements therein contained and binding upon Tenant. Any of Landlord's Work in
a Portion of the Premises not fully completed on the Term Commencement Date in
respect of such Portion shall be so completed by Landlord within thirty (30)
days after the Term Commencement Date in respect of such Portion (other than
long-lead items which shall be completed with reasonable diligence by Landlord).

         (b) Definition of Tenant Delays. For the purposes hereof, a "Tenant
Delay" shall be defined as a delay in the performance of Landlord's Work: (i)
due to special work (i.e., long - lead items of which Landlord advises Tenant at
the time Landlord approves Tenant's final plans in respect of a Portion of the
Premises), changes, alterations or additions required or made by Tenant in the
layout or finish of either Portion of the Premises or any part thereof, (ii)
caused in whole or in part by Tenant through the delay of Tenant in submitting
any plans and/or specifications, supplying information, approving plans,
specifications or estimates, giving authorizations or otherwise or (iii) caused
in whole or in part by delay and/or default on the part of Tenant or its
contractors including, without limitation, the utility companies and other
entities furnishing communications, data processing or other service or
equipment.

         4.3 PLANS AND SPECIFICATIONS. Tenant shall be solely responsible for
the timely preparation and submission to Landlord of the final architectural,
electrical and mechanical construction drawings, plans and specifications
(called "plans") necessary to construct each Portion of the Premises for
Tenant's occupancy, which plans shall be subject to approval by Landlord's
architect and engineers, which approval shall not be unreasonably withheld, and
shall comply with their requirements to avoid aesthetic or other conflicts with
the design and function of the balance of the Building. Landlord's approval is
solely given for the benefit of Landlord and neither Tenant nor any third party
shall have the right to rely upon Landlord's approval of Tenant's plans for any
purpose whatsoever. Without limiting the foregoing, Tenant shall be responsible
for all elements of the design of Tenant's plans (including, without limitation,
compliance with law, functionality of design, the structural integrity of the
design, the configuration of each Portion of the Premises and the placement of
Tenant's furniture, appliances and equipment), and Landlord's approval of
Tenant's plans shall in no event relieve Tenant of the responsibility for such
design. Tenant has assured itself by direct communication with the architect and
engineers (Landlord's or its own, as the case may be) that the final approved
plans can be delivered to Landlord on or before the Final Plans Date in respect
of each Portion of the Premises as stated in Exhibit 1, provided that Tenant
promptly furnishes complete information concerning its requirements to said
architect and engineers as and when requested by them; and Tenant covenants and
agrees to cause said final, approved plans and specifications to be delivered to
Landlord on or before said respective Final Plans Dates and to devote such time
as may be necessary in consultation with said architect and engineers to enable
them to complete and submit all plans within the required time limit. Time is of
the essence in respect of preparation and submission of plans by Tenant. (The
word "architect" as used in this Article 4 shall include an interior designer or
space planner.)

         4.4 PREPARATION OF PREMISES.

                  (a) By Landlord. Except as is otherwise herein provided or as
may be otherwise approved by the Landlord, all work necessary to prepare each
Portion of the Premises for Tenant's occupancy, including work to be performed
at Tenant's expense, shall be performed by contractors

                                      -4-
<PAGE>   14
employed by Landlord. Notwithstanding the foregoing, the work described in
Exhibit 6 as "Base Building Work" shall be performed by Landlord at Landlord's
expense. Landlord's contract with the general contractor for Landlord's Work in
each Portion of the Premises shall provide for a fixed fee of four percent (4%),
and the fee in connection with change orders shall be four percent (4%), which
shall include overhead and profit but not general conditions, which fees shall
be subject to adjustment by reason of changes or by reason of Tenant Delays.
Landlord shall cause Landlord's general contractor to obtain at least three (3)
subcontractor bids for each trade in connection with Landlord's Work in each
Portion of the Premises. Tenant shall have the right to propose subcontractors
for each trade for the Landlord's Work in each Portion of the Premises, which
subcontractors shall be subject to Landlord's prior consent, not to be
unreasonably withheld. Landlord shall provide to Tenant "open book" access to
the contracting for and pricing of Landlord's Work in respect of each Portion of
the Premises.

         In addition, Landlord shall contribute up to Thirty and 00/100 ($30.00)
Dollars per square foot of Total Rentable Area of each Portion of the Premises
("Landlord's Contribution") towards the cost of Landlord's Work in such Portion
of the Premises. Notwithstanding the foregoing, overtime costs and costs
resulting from the negligence of the Landlord or its contractors shall not be
charged against Landlord's Contribution. Tenant shall, within thirty (30) days
of billing therefor, together with reasonable backup to evidence such costs,
reimburse Landlord for all costs of Landlord's Work in excess of Landlord's
Contribution. Tenant shall have the right to apply any unused portion of
Landlord's Contribution towards (i) the architectural and engineering fees
incurred by Tenant in connection with Landlord's Work, and (ii) the generator to
be installed by Tenant at the Premises. Landlord shall reimburse Tenant for such
unused portion of Landlord's Contribution within thirty (30) days after
Landlord's receipt of paid invoices evidencing such costs. Except as set forth
in the immediately preceding two (2) sentences, Tenant shall have no right to
use any unused portion of Landlord's Contribution.

                  (b) By Tenant. Subject always to the provisions of Articles
4.2 and 4.3, if Tenant will be employing any contractors in preparing either
Portion of the Premises for Tenant's occupancy, Landlord will give Tenant
reasonable advance notice of the date on which such Portion of the Premises will
be ready for such other contractors and a reasonable time will be allowed from
such date for doing the work to be performed by such other contractors.

                  (c) If any work, including but not by way of limitation,
installation of built-in equipment by the manufacturer or distributor thereof,
shall be performed by contractors not employed by Landlord, Tenant shall take
necessary reasonable measures to the end that such contractor shall cooperate in
all ways with Landlord's contractors to avoid any delay to the work being
performed by Landlord's contractors or conflict in any other way with the
performance of such work.

         4.5 QUALITY AND COST OF MATERIALS. (i) Any construction or finish of
the Premises, whether by Landlord or Tenant, shall equal or exceed the
specifications and quantities provided in Exhibit 3. (ii) Except for Landlord's
Contribution, Tenant shall bear all other costs of preparing the Premises for
its occupancy in accordance with Tenant's plans including, without limitation,
the cost of substitutes for any items specified in Exhibit 3.

         4.6 TENANT'S DELAY - ADDITIONAL COSTS. In the event of a Tenant Delay,
any additional cost to Landlord in connection with the completion of each
Portion of the Premises in accordance with the terms of this Lease and Exhibit 4
shall be promptly paid by Tenant to Landlord if such additional cost is in whole
or in part the result of such failure, omission or delay of Tenant (provided
however, that if Tenant is only partially responsible for a delay, i.e. because
of delay caused by Landlord or Landlord's contractor, Tenant shall be charged
for additional costs only to the extent of Tenant's partial responsibility). For
the purposes of the next preceding sentence, the expression "additional cost to
Landlord" shall mean the actual, out-of-pocket cost over and above such cost as
would have been the aggregate cost to Landlord of completing such Portion of the
Premises in accordance with the terms of

                                      -5-
<PAGE>   15
this Lease and Exhibit 4 had there been no such Tenant Delay. Nothing contained
in this Article 4.6 shall limit or qualify or prejudice any other covenants,
agreements, terms, provisions and conditions contained in this Lease, including,
but not limited to Article 4.2.

         4.7 ENTRY BY TENANT PRIOR TO TERM COMMENCEMENT DATE. With Landlord's
prior written consent, which shall not be unreasonably withheld, Tenant shall
have the right to enter each Portion of the Premises prior to the Term
Commencement Date in respect of such Portion, during normal business hours and
without payment of rent, to perform such work or decoration as is to be
performed by, or under the direction or control of, Tenant and as is otherwise
in compliance with the terms of this Lease. Such right of entry shall be deemed
a license from Landlord to Tenant, and any entry thereunder shall be at the risk
of Tenant.

         4.8 CONCLUSIVENESS OF LANDLORD'S PERFORMANCE. With respect to patent
defects in any portion of Landlord's Work, Tenant shall be conclusively deemed
to have agreed that Landlord has performed all of its obligations under this
Article 4 with respect to each Portion of the Premises unless not later than the
end of the fourth calendar month next beginning after the Term Commencement Date
in respect of such Portion of the Premises Tenant shall give Landlord written
notice specifying the respects in which Landlord has not performed any such
obligation. With respect to latent defects in any portion of Landlord's Work,
Tenant shall be conclusively deemed to have agreed that Landlord has performed
all of its obligations under this Article 4 with respect to each Portion of the
Premises unless, not later than the date eleven (11) months after the date
Landlord substantially completes Landlord's Work in such Portion of the
Premises, Tenant shall give written notice to Landlord specifying the respects
in which Landlord has not performed any such obligation.

         4.9 TENANT PAYMENTS OF CONSTRUCTION COST. Landlord shall have the same
rights and remedies which Landlord has upon the nonpayment of Yearly Rent and
other charges due under this Lease for nonpayment of any amounts which Tenant is
required to pay to Landlord or Landlord's contractor in connection with the
construction and initial preparation of the Premises (including, without
limitation, any amounts which Tenant is required to pay in accordance with
Articles 4.5 and 4.6 hereof) or in connection with any construction in the
Premises performed for Tenant by Landlord, Landlord's contractor or any other
person, firm or entity after the Term Commencement Date in respect of either
Portion of the Premises.

5.       USE OF PREMISES

         5.1 PERMITTED USE. Tenant shall continuously during the term hereof
occupy and use the Premises only for the purposes as stated in Exhibit 1 and for
no other purposes. Service and utility areas (whether or not a part of the
Premises) shall be used only for the particular purpose for which they were
designed. Without limiting the generality of the foregoing, Tenant agrees that
it shall not use the Premises or any part thereof, or permit the Premises or any
part thereof to be used for the preparation or dispensing of food, whether by
vending machines or otherwise. Notwithstanding the foregoing, but subject to the
other terms and provisions of this Lease, Tenant may, with Landlord's prior
written consent, which consent shall not be unreasonably withheld, install at
its own cost and expense so-called hot-cold water fountains, coffee makers and
refrigerator-sink-stove combinations for the preparation of beverages and foods,
provided that no cooking, frying, etc., are carried on in the Premises to such
extent as requires special exhaust venting, Tenant hereby acknowledging that the
Building is not engineered to provide any such special venting. Landlord hereby
agrees that any equipment shown on Tenant's final approved plans and equivalent
equipment in substitution of such equipment shall not, if maintained in good
operating order, be deemed to violate the provisions of this Article 5.2.

         5.2 PROHIBITED USES. Notwithstanding any other provision of this Lease,
Tenant shall not use, or suffer or permit the use or occupancy of, or suffer or
permit anything to be done in or anything to be brought into or kept in or about
the Premises or the Building or any part thereof (including, without

                                      -6-
<PAGE>   16
limitation, any materials appliances or equipment used in the construction or
other preparation of the Premises and furniture and carpeting): (i) which would
violate any of the covenants, agreements, terms, provisions and conditions of
this Lease or otherwise applicable to or binding upon the Premises; (ii) for any
unlawful purposes or in any unlawful manner; (iii) which, in the reasonable
judgment of Landlord shall in any way (a) impair the appearance or reputation of
the Building; or (b) impair, interfere with or otherwise diminish the quality of
any of the Building services or the proper and economic heating, cleaning,
ventilating, air conditioning or other servicing of the Building; or Premises,
or with the use or occupancy of any of the other areas of the Building, or
occasion discomfort, inconvenience or annoyance, or injury or damage to any
occupants of the Premises or other tenants or occupants of the Building; or (iv)
which is inconsistent with the maintenance of the Building as an office building
of the first class in the quality of its maintenance, use, or occupancy. Tenant
shall not install or use any electrical or other equipment of any kind which, in
the reasonable judgment of Landlord, might cause any such impairment,
interference, discomfort, inconvenience, annoyance or injury.

         5.3 LICENSES AND PERMITS. If any governmental license or permit shall
be required for the proper and lawful conduct of Tenant's business, and if the
failure to secure such license or permit would in any way affect Landlord, the
Premises, the Building or Tenant's ability to perform any of its obligations
under this Lease, Tenant, at Tenant's expense, shall duly procure and thereafter
maintain such license and submit the same to inspection by Landlord. Tenant, at
Tenant's expense, shall at all times comply with the terms and conditions of
each such license or permit. Tenant shall furnish all data and information to
governmental authorities and Landlord as required in accordance with legal,
regulatory, licensing or other similar requirements as they relate to Tenant's
use or occupancy of the Premises or the Building.

6.       RENT

         (a) During the term of this Lease the Yearly Rent and other charges, at
the rate stated in Exhibit 1, shall be payable by Tenant to Landlord by monthly
payments, as stated in Exhibit 1, in advance and without demand on the first day
of each month for and in respect of such month. The rent and other charges
reserved and covenanted to be paid under this Lease in respect of each Portion
of the Premises shall commence on the Term Commencement Date in respect of such
Portion of the Premises, provided however, that Tenant's obligation to pay
Yearly Rent, Tax Excess or Operating Expense Excess in respect of the third
(3rd) floor of the Premises shall not commence to accrue until the date eight
(8) months after the Term Commencement Date in respect of Portion A.
Notwithstanding the provisions of the next preceding sentence, Tenant shall pay
the first monthly installment of rent (other than for the third (3rd) floor of
the Premises) on the execution of this Lease. If, by reason of any provisions of
this Lease, the rent reserved hereunder shall commence or terminate on any day
other than the first day of a calendar month, the rent for such calendar month
shall be prorated. The rent shall be payable to Landlord or, if Landlord shall
so direct in writing, to Landlord's agent or nominee, in lawful money of the
United States which shall be legal tender for payment of all debts and dues,
public and private, at the time of payment, at the office of the Landlord or
such place as Landlord may designate, and the rent and other charges in all
circumstances shall be payable without any setoff or deduction whatsoever.
Rental and any other sums due hereunder not paid on or before the date which is
five (5) business days after the date due shall bear interest for each month or
fraction thereof from the due date until paid computed at the annual rate of
three percentage points over the so-called prime rate then currently from time
to time charged to its most favored corporate customers by the largest national
bank (N.A.) located in the city in which the Building is located ("National
Bank"), or at any applicable lesser maximum legally permissible rate for debts
of this nature. In lieu of requiring Tenant to pay monthly installments of
Yearly Rent and other fixed monthly charges in the manner described above,
Tenant shall have the right to pay such amounts by means of an automated debit
system (the "Automatic Debit System") whereby any or all such payments shall be
debited from Tenant's account in a bank or financial institution designated by
Tenant and credited to Landlord's account in a bank or financial institution
designated by Landlord. In the event Tenant elects to pay monthly installments
of Yearly Rent and other fixed monthly charges by means of the Automatic Debit
System, Tenant, within thirty (30) days after written request by Landlord, shall
execute and deliver

                                      -7-
<PAGE>   17
to Landlord any authorizations, certificates or other documentation as may be
required to establish and give effect to the Automatic Debit System. Either
party shall have the right to change its bank or financial institution from time
to time, provided that Tenant, no less than thirty (30) days prior to the
effective date of any such change, shall provide Landlord with written notice of
such change and any and all authorizations, certificates or other documentation
as may be required to establish and give effect to the Automatic Debit System at
Tenant's new bank or financial institution if Tenant elects to continue to use
such Automatic Debit System. Tenant shall promptly pay all service fees and
other charges imposed upon Tenant in connection with the Automatic Debit System,
and Tenant shall promptly reimburse Landlord for any charges resulting from
insufficient funds in Tenant's bank account (provided however, that Tenant shall
have the right to discontinue the use of the Automatic Debit System at any time
upon at least thirty (30) days' prior written notice to Landlord). In the event
that any Yearly Rent or other fixed monthly charges are not paid on time as a
result of insufficient funds in Tenant's account, Tenant shall be liable for any
interest in accordance with this Article. Tenant shall remain liable to Landlord
for all payments of Rent due hereunder regardless of whether Tenant's account is
incorrectly debited in any given month, it being agreed that a debit of less
than the full amount due shall not be construed as a waiver by Landlord of its
right to receive any unpaid balance.

         (b) Rentable Area. Landlord and Tenant acknowledge the Total Rentable
Area of the Premises, the Building and of the other buildings initially in the
Complex have been determined by agreement, and that the figures set forth in
Exhibit 1 shall be conclusive and binding on Landlord and Tenant with regard to
the Complex. Landlord and Tenant acknowledge that the figure set forth in
Exhibit 1 for the Total Rentable Area of the Complex does not include the floor
area of the building known as 549 Technology Square, as that building is
currently vacant. The Total Rentable Area of the Complex shall not include the
floor area of Building 549 unless and until: (i) Landlord executes a lease with
respect to all or any portion of Building 549 for a term of less than two (2)
years and such tenant is in actual occupancy of such space for at least six (6)
months, in which case the Total Rentable Area of the Complex shall include the
floor area of Building 549 throughout the time of occupancy of such tenant in
Building 549, or (ii) if Landlord executes a lease with respect to all or any
portion of Building 549 with a term of two (2) years or more, in which case the
Total Rentable Area of the Complex shall thereafter include the floor area of
Building 549 as of the commencement of occupancy of Building 549 by such tenant;
provided however, that upon the demolition of Building 549, the Total Rentable
Area of Building 549 shall thereafter be excluded from the Total Rentable Area
of the Complex. In the event that Landlord alters any of the buildings in, or
adds other buildings to, the Complex, the Total Rentable Area of any such
buildings shall be included in the Total Rentable Area of the Complex when first
occupied.

7.       RENTABLE AREA

         Total Rentable Area of the Premises, the Building and the Complex have,
as of the Execution Date, been agreed to be the amounts set forth on Exhibit 1.

8.       SERVICES FURNISHED BY LANDLORD

         8.1 ELECTRIC CURRENT.

                  (a) As stated in Exhibit 1, Landlord will require Tenant to
contract directly with the company supplying electric current for the purchase
and obtaining by Tenant of electric current directly from such company to be
billed directly to, and paid for by, Tenant. Tenant shall have the right to
choose among companies supplying electric current to the Premises if there is
more than one such company available.

                  (b) Landlord shall (i) permit its risers, conduits and feeders
to the extent available, suitable and safely capable, to be used for the purpose
of enabling Tenant to purchase and obtain electric current directly from such
company, (ii) without cost or charge to Tenant, make such alterations and


                                      -8-
<PAGE>   18
additions to the electrical equipment and/or appliances in the Building as such
company shall specify for the purpose of enabling Tenant to purchase and obtain
electric current directly from such company, and (iii) at Landlord's expense,
furnish and install in or near the Premises any necessary metering equipment
used in connection with measuring Tenant's consumption of electric current and
Tenant, at Tenant's expense, shall maintain and keep in repair such metering
equipment.

                  (c) Tenant shall require electric current for use in the
Premises in excess of the capacity available at the commencement of the term of
this Lease and if (i) in Landlord's reasonable judgment, Landlord's facilities
are inadequate for such excess requirements or (ii) such excess use shall result
in an additional burden on the Building air conditioning system and additional
cost to Landlord on account thereof then, as the case may be, (x) Landlord upon
written request and at the sole cost and expense of Tenant, will furnish and
install such additional wire, conduits, feeders, switchboards and appurtenances
as reasonably may be required to supply such additional requirements of Tenant
if current therefor be available to Landlord, provided that the same shall be
permitted by applicable laws and insurance regulations and shall not cause
damage to the Building or the Premises or cause or create a dangerous or
hazardous condition or entail excessive or unreasonable alterations or repairs
or interfere with or disturb other tenants or occupants of the Building or (y)
Tenant shall reimburse Landlord for such additional cost, as aforesaid.

                  (e) Landlord, at Tenant's expense and upon Tenant's request,
shall purchase and install all replacement lamps of types generally commercially
available (including, but not limited to, incandescent and fluorescent) used in
the Premises.

                  (f) Subject to Article 8.8 (b), Landlord shall not in any way
be liable or responsible to Tenant for any loss, damage or expense which Tenant
may sustain or incur if the quantity, character, or supply of electrical energy
is changed or is no longer available or suitable for Tenant's requirements.

                  (g) Tenant agrees that it will not make any material
alteration or material addition to the electrical equipment and/or appliances in
the Premises without the prior written consent of Landlord in each instance
first obtained, which consent will not be unreasonably withheld, and will
promptly advise Landlord of any other alteration or addition to such electrical
equipment and/or appliances.

         8.2 WATER. Landlord shall furnish hot and cold water for ordinary
premises cleaning, toilet, lavatory and drinking purposes. If Tenant requires,
uses or consumes water for any purpose other than for the aforementioned
purposes, Landlord may (i) assess a reasonable charge for the additional water
so used or consumed by Tenant or (ii) install a water meter and thereby measure
Tenant's water consumption for all purposes. In the latter event, Landlord shall
pay the cost of the meter and the cost of installation thereof and shall keep
said meter and installation equipment in good working order and repair. Tenant
agrees to pay for water consumed, as shown on said meter, together with the
sewer charge based on said meter charges, as and when bills are rendered, and on
default in making such payment Landlord may pay such charges and collect the
same from Tenant, but only to the extent that the charges shown on the meter
exceed the consumption reasonably expected for ordinary premises cleaning,
toilet, lavatory and drinking purposes. All piping and other equipment and
facilities for use of water outside the building core will be installed and
maintained by Landlord at Tenant's sole cost and expense.

         8.3 ELEVATORS, HEAT, CLEANING.

                  (a) Landlord at its expense shall: (i) provide necessary
elevator facilities (which may be manually or automatically operated, either or
both, as Landlord may from time to time elect) on Mondays through Fridays,
excepting legal holidays, from 8:00 a.m. to 6:00 p.m. and on Saturdays,
excepting legal holidays, from 8:00 a.m. to 1:00 p.m. (called "business days")
and have one elevator in operation available for Tenant's use, non-exclusively,
together with others having business in the

                                      -9-
<PAGE>   19
Building, at all other times; (ii) furnish heat (substantially equivalent to
that being furnished in comparably aged similarly equipped office buildings in
the same city) to the Premises during the normal heating season on business
days; and (iii) cause the office areas [and the network operations center] of
the Premises to be cleaned on business days (except on Saturdays) provided the
same are kept in order by Tenant. Either Exhibit 4 (if annexed hereto) or,
otherwise, the cleaning standards generally prevailing in first-class office
buildings in the city or town where the Building is located, shall represent
substantially the extent and scope of the cleaning by Landlord referred to in
this Article 8.3.

                  (b) The parties agree and acknowledge that, despite reasonable
precautions in selecting cleaning and maintenance contractors and personnel, any
property or equipment in the Premises of a delicate, fragile or vulnerable
nature may nevertheless be damaged in the course of cleaning and maintenance
services being performed. Accordingly, Tenant shall take reasonable protective
precautions with such property and equipment (including, without limitation,
computers or other data processing components or equipment and optical or
electronic equipment, etc.), e.g., housing the property and equipment in a
separate, locked room, so as to render it inaccessible to the Building's
cleaning personnel.

         8.4 AIR CONDITIONING. Landlord shall through the air conditioning
equipment of the Building furnish to and distribute in the Premises air
conditioning as normal seasonal changes may require on business days during the
hours as aforesaid in Article 8.3 when air conditioning may reasonably be
required for the comfortable occupancy of the Premises by Tenant. Tenant agrees
to use reasonable efforts to lower and close the blinds or drapes when necessary
because of the sun's position, whenever the air conditioning system is in
operation, and to cooperate fully with Landlord with regard to, and to abide by
all the reasonable regulations and requirements which Landlord may prescribe for
the proper functioning and protection of the air conditioning system. The air
conditioning system referred to in this Article 8.4 shall be capable of
maintaining the following: the air conditioning system referred to in this
Article 8.4 shall be capable of providing 75(Degree)F dry bulb and 55% of
relative humidity with outside conditions of 91(Degree)F dry bulb and
73(Degree)F wet bulb.

         8.5 ADDITIONAL HEAT, CLEANING AND AIR CONDITIONING SERVICES.

                  (a) Landlord will use reasonable efforts upon reasonable
advance written notice from Tenant of its requirements in that regard, to
furnish additional heat, cleaning or air conditioning services to the Premises
on days and at times other than as above provided.

                  (b) Tenant will pay to Landlord a reasonable charge (i) for
any such additional heat, cleaning or air conditioning service required by
Tenant, (ii) for any extra cleaning of the Premises required because of the
carelessness or indifference of Tenant or because of the nature of Tenant's
business, and (iii) for any cleaning done at the request of Tenant of any
portions of the Premises which may be used for storage, shipping room or other
non-office purposes. If the cost to Landlord for cleaning the Premises shall be
increased due to the installation in the Premises, at Tenant's request, of any
materials or finish other than those which are building standard, Tenant shall
pay to Landlord an amount equal to such increase in cost. As of the Execution
Date of the Lease, the charge for additional heat and air conditioning is $65.25
per hour. Said charge shall only be increased in relation to the increase in
actual costs incurred by Landlord in providing such service including, without
limitation, overhead and depreciation, but excluding any profit to Landlord.
Notwithstanding the foregoing, in no event shall the overhead component of such
charge at any time exceed five percent (5%) of the total charge.

         8.6 ADDITIONAL AIR CONDITIONING EQUIPMENT. In the event Tenant requires
additional air conditioning for business machines, meeting rooms or other
special purposes, or because of occupancy or excess electrical loads, any
additional air conditioning units, chillers, condensers, compressors, ducts,
piping and other equipment, such additional air conditioning equipment will be
installed and maintained by Landlord at Tenant's sole cost and expense, but only
if, in Landlord's reasonable judgment, the same will not cause damage or injury
to the Building or create a dangerous or hazardous condition or entail

                                      -10-
<PAGE>   20
excessive or unreasonable alterations, repairs or expense or interfere with or
disturb other tenants; and Tenant shall reimburse Landlord in such an amount as
will compensate it for the cost incurred by it in operating such additional air
conditioning equipment.

         8.7 REPAIRS. Except as otherwise provided in Articles 18 and 20, and
subject to Tenant's obligations in Article 14, Landlord shall keep and maintain
the roof, exterior walls, structural floor slabs, columns, elevators, public
stairways and corridors, lavatories, equipment (including, without limitation,
sanitary, electrical, heating, air conditioning, or other systems) and other
common facilities of the Building in good condition and repair.

         8.8 INTERRUPTION OR CURTAILMENT OF SERVICES. (a) When necessary by
reason of accident or emergency, or for repairs, alterations, replacements or
improvements which in the reasonable judgment of Landlord are desirable or
necessary to be made, or of difficulty or inability in securing supplies or
labor, or of strikes, or of any other cause beyond the reasonable control of
Landlord, whether such other cause be similar or dissimilar to those hereinabove
specifically mentioned until said cause has been removed, Landlord reserves the
right to interrupt, curtail, stop or suspend (i) the furnishing of heating,
elevator, air conditioning, and cleaning services and (ii) the operation of the
plumbing and electric systems. Landlord shall exercise reasonable diligence to
eliminate the cause of any such interruption, curtailment, stoppage or
suspension, but there shall be no diminution or abatement of rent or other
compensation due from Landlord to Tenant hereunder, nor shall this Lease be
affected or any of the Tenant's obligations hereunder reduced, and the Landlord
shall have no responsibility or liability for any such interruption,
curtailment, stoppage, or suspension of services or systems.

         (b) Notwithstanding anything to the contrary in this Lease contained,
if the Premises shall lack any service which Landlord is required to provide
hereunder, or if Tenant's use and occupancy of the Premises shall be disturbed
in violation of Article 10 hereof (thereby rendering the Premises or a portion
thereof substantially untenantable) so that, for the Landlord Service
Interruption Cure Period, as hereinafter defined, the continued operation in the
ordinary course of Tenant's business is materially adversely affected and if
Tenant ceases to use the affected portion of the Premises during the period of
untenantability as the direct result of such lack of service or disturbance,
then, provided that Tenant ceases to use the affected portion of the Premises
during the entirety of the Landlord Service Interruption Cure Period and that
such untenantability and Landlord's inability to cure such condition is not
caused by the fault or neglect of Tenant or Tenant's agents, employees or
contractors, Yearly Rent, Operating Expense Excess and Tax Excess shall
thereafter be abated in proportion to such untenantability until the day such
condition is completely corrected. For the purposes hereof, the "Landlord
Service Interruption Cure Period" shall be defined as five (5) consecutive
business days after Landlord's receipt of written notice from Tenant of the
condition causing untenantability in the Premises, provided however, that the
Landlord Service Interruption Cure Period shall be ten (10) consecutive business
days after Landlord's receipt of written notice from Tenant of such condition
causing untenantability in the Premises if either the condition was caused by
causes beyond Landlord's control or Landlord is unable to cure such condition as
the result of causes beyond Landlord's control.

         (c) The provisions of Paragraph (b) of this Article 8.8 shall not apply
in the event of untenantability caused by fire or other casualty, or taking (see
Articles 18 and 20).

         8.9 ENERGY CONSERVATION. Notwithstanding anything to the contrary in
this Article 8 or in this Lease contained, Landlord may institute, and Tenant
shall comply with, such policies, programs and measures as may be necessary,
required, or expedient for the conservation and/or preservation of energy or
energy services, provided however, that Landlord does not, by reason of such
policies, programs and measures, reduce the level of energy or energy services
being provided to the premises below the level of energy or energy services then
being provided in comparably aged, first-class office buildings in the greater
Boston area, or as may be necessary or required to comply with applicable codes,
rules regulations or standards.


                                      -11-
<PAGE>   21
         8.10 MISCELLANEOUS. Other than air conditioning, all services provided
by Landlord to Tenant are based upon an assumed maximum Premises population of
one person per one hundred fifty (150) square feet of Total Rentable Area.
Tenant acknowledges that if it exceeds the foregoing limitation, Landlord may
incur costs including, without limitation, additional costs due to the
additional load on building systems. Tenant agrees to reimburse Landlord for the
amount of such costs (if any), as reasonably determined by Landlord, due to a
Premises population in excess of the foregoing maximum.

9.       ESCALATION

         9.1 DEFINITIONS. As used in this Article 9, the words and terms which
follow mean and include the following:

                  (a) "Operating Year" shall mean a calendar year in which
occurs any part of the term of this Lease.

                  (b) "Building Operating Cost Base" and "Complex Operating Cost
Base" shall be determined as stated in Exhibit 1.

                  (c) Subject to the provisions of Article 6(b), "Tenant's
Building Operating Cost Percentage," "Tenant's Complex Operating Cost
Percentage," and "Tenant's Building Tax Percentage," shall be determined as
stated in Exhibit 1.

                  (d) "Taxes":

                           (d1) "Building Taxes" shall mean the real estate
         taxes and other taxes, levies and assessments imposed upon the Building
         and that portion of the land of the Complex comprised of the Building's
         footprint and an area surrounding the Building as shown on Exhibit 4,
         and upon any personal property of Landlord used in the operation of the
         Building, or on Landlord's interest in the Building or such personal
         property (provided that to the extent such taxes, levies, and
         assessments are also allocable to property other than the Building,
         such amounts shall be allocated among all real estate which is so
         jointly assessed based on the assessor's records or, if the records do
         not provide a separate allocation, based on square footage of the
         buildings in question); charges, fees and assessments for transit,
         housing, police, fire or other services or purported benefits to the
         Building; service or user payments in lieu of taxes; and any and all
         other taxes, levies, betterments, assessments and charges arising from
         the ownership, leasing, operating, use or occupancy of the Building or
         based upon rentals derived therefrom, which are or shall be imposed by
         federal, state, county, municipal or other governmental authorities.
         Notwithstanding anything to the contrary herein contained, with respect
         to betterments or other extraordinary or special assessments, Tenant's
         obligations shall apply only to the extent such assessments are payable
         during and in respect of the term of the Lease if paid over the longest
         period permitted by law. The definition of Building Taxes is subject to
         the provisions of Article 9.1(d4)

                           (d2) "Land" shall mean all of the land of the Complex
         (but not any improvements thereon which are separately assessed, except
         for common facilities as set forth in Paragraph (d3) below), excluding,
         however, the land on which the Garage and all other parking areas are
         located and the portions of land under each building in the Complex
         (but not Building 549, except as hereinafter provided) and an area
         surrounding each such building as shown on Exhibit 4. Real estate taxes
         with respect to such parking areas are included in the parking fees
         charged to users and real estate taxes attributable to the land
         comprised of the footprint and such perimeter area of each building in
         the Complex (but not Building 549, except as hereinafter provided)
         shall be allocated on a building-by-building basis. Until such time as
         the floor area of

                                      -12-
<PAGE>   22
         Building 549 is included in the Total Rentable Area of the Complex
         pursuant to Article 6(b), all of the buildings from time to time in the
         Complex shall share the cost of real estate taxes attributable to
         Building 549's footprint and the area surrounding Building 549 as shown
         on Exhibit 4. If at any time, however, the floor area of Building 549
         is included in the Total Rentable Area of the Complex pursuant to
         Article 6(b), the real estate taxes attributable to the land comprised
         of Building 549's footprint and such Building 549 perimeter area shall
         be allocated in full to the tenant or tenants of Building 549.

                           (d3) "Land Taxes" shall mean the real estate taxes
         and other taxes, levies and assessments imposed upon the Land, upon any
         common facilities separately assessed as such by the tax assessor, and
         upon any personal property of Landlord used in connection with the
         Land, or on Landlord's interest in the Land or such personal property
         (provided that to the extent such taxes, levies, and assessments are
         also allocable to property other than the Land, such amounts shall be
         equitably allocated among all real estate which is so jointly
         assessed); charges, fees and assessments for transit, housing, police,
         fire or other governmental services or purported benefits to the Land;
         service or user payments in lieu of taxes; and any and all other taxes,
         levies, betterments, assessments and charges arising from the
         ownership, leasing, operating, or use of the Land or based upon rentals
         derived therefrom, which are or shall be imposed by federal, state,
         county, municipal or other governmental authorities. Land Taxes shall
         exclude any taxes on any parking garage located on the Land. The
         definition of Land Taxes is subject to the provisions of Article
         9.1(d4).

                           (d4) As of the Execution Date, neither Building Taxes
         nor Land Taxes shall include any inheritance, estate, succession, gift,
         franchise, rental, income or profit tax, capital stock tax, capital
         levy or excise, or any income taxes arising out of or related to the
         ownership and operation of the Building or Complex, provided, however,
         that any of the same and any other tax, excise, fee, levy, charge or
         assessment, however described, that may in the future be levied or
         assessed as a substitute for or an addition to, in whole or in part,
         any tax, levy or assessment which would otherwise constitute "Taxes,"
         whether or not now customary or in the contemplation of the parties on
         the Execution Date of this Lease, shall constitute "Taxes," but only to
         the extent calculated as if the Complex were the only real estate owned
         by Landlord. "Taxes" shall also include reasonable expenses of tax
         abatement or other proceedings contesting assessments or levies.

                  (e) "Building Tax Base" shall be the amount determined as set
forth in Exhibit 1 and shall apply to a Tax Period of twelve (12) months. The
Building Tax Base shall be reduced pro rata if and to the extent that the Tax
Period contains fewer than twelve (12) months.

                  (f) "Tax Period" shall be any fiscal/tax period in respect of
which Taxes are due and payable to the appropriate governmental taxing authority
(i.e., as mandated by the governmental taxing authority), any portion of which
period occurs during the term of this Lease, the first such Tax Period being
fiscal tax year 2000.

                  (g) "Operating Costs":

                           (g1) Definition of Building Operating Costs.
         "Building Operating Costs" shall mean all costs incurred and
         expenditures of whatever nature made by Landlord in the operation and
         management, for repair and replacements, cleaning and maintenance of
         the Building, including, without limitation, vehicular and pedestrian
         passageways serving the Building, related equipment, facilities and
         appurtenances and cooling and heating equipment

                           (g2) Definition of Complex Operating Costs. "Complex
         Operating Costs" shall mean all costs incurred and expenditures made by
         Landlord in the operation and

                                      -13-
<PAGE>   23
         management, for repair and replacements, cleaning and maintenance of
         the Complex, exclusive of the Garage, the Parking Areas, the Building,
         and other buildings in the Complex, and Land Taxes. Any expenses
         incurred by Landlord that can be allocated on a building-by-building
         basis shall be so allocated in accordance with Subparagraph (g3). To
         the extent that a cost included in Complex Operating Costs is also
         allocable to property other than the Complex, such cost shall be
         equitably allocated to each parcel of property which benefits from such
         cost. Whether or not Building 549 is included in the Total Rentable
         Area of the Complex in accordance with Article 6(b), any amounts
         collected by Landlord from tenants of Building 549 for Complex
         Operating Costs during any Operating Year shall be applied to reduce
         Complex Operating Expenses for such Operating Year.

                           (g3) The allocation of costs and expenditures among
         the various buildings in the Complex shall be on the basis of the ratio
         of the Total Rentable Area of each building in the Complex to the Total
         Rentable Area of the Complex, unless such allocation would result in a
         disproportionate charge based upon the relative usage of the service on
         which such cost is based, in which case such allocation shall be based
         upon such relative usage. Building Operating Costs and Complex
         Operating Costs shall include, without limitation, those categories of
         "Specifically Included Operating Costs", as set forth below, but shall
         not include "Excluded Costs", as hereinafter defined.

                           (g4) Definition of Excluded Costs. "Excluded Costs"
                  shall be defined as:

                                    (i)      mortgage charges (including
                                             interest, principal, points and
                                             fees);

                                    (ii)    brokerage commissions;

                                    (iii)   salaries of executives and owners
                                            not directly employed in the
                                            management/operation of the Complex;

                                    (iv)    the cost of work done by Landlord
                                            for a particular tenant for which
                                            Landlord has the right to be
                                            reimbursed by such tenant;

                                    (v)     subject to Subparagraph (g5) below,
                                            such portion of expenditures as are
                                            not properly chargeable against
                                            income;

                                    (vi)     any ground or underlying lease
                                             rental;

                                    (vii)   bad debt expenses;

                                    (viii)  costs incurred by Landlord to the
                                            extent that Landlord is reimbursed
                                            by insurance proceeds or is
                                            otherwise reimbursed, other than
                                            through the payment of Operating
                                            Costs;

                                    (ix)     depreciation, amortization and
                                             interest payments, except as
                                             expressly set forth in subparagraph
                                             (g5) below and except on equipment,
                                             materials, tools, supplies and
                                             vendor-type equipment purchased by
                                             Landlord to enable Landlord to
                                             supply services Landlord might
                                             otherwise contract for with a third
                                             party where such depreciation,
                                             amortization and interest payments
                                             would otherwise have been included
                                             in the charge for such third
                                             party's services, all as determined
                                             in

                                      -14-
<PAGE>   24
                                             accordance with generally accepted
                                             accounting principles, consistently
                                             applied, and when depreciation or
                                             amortization is permitted or
                                             required, the item shall be
                                             amortized over its reasonably
                                             anticipated useful life;

                                    (x)      advertising and promotional
                                             expenditures, and costs of
                                             acquisition and maintenance of
                                             one-party signs in or on the
                                             Building identifying the owner of
                                             the Building or other tenants;

                                    (xi)     marketing costs, including leasing
                                             commissions, attorneys' fees (in
                                             connection with the negotiation and
                                             preparation of letters, deal memos,
                                             letters of intent, leases,
                                             subleases and/or assignments),
                                             space planning costs and other
                                             costs and expenses incurred in
                                             connection with lease, sublease
                                             and/or assignment negotiations and
                                             transactions with present or
                                             prospective tenants or other
                                             occupants of the Building;

                                    (xii)    costs, including permit, license
                                             and inspection costs, incurred with
                                             respect to the installation of
                                             tenants' or other occupants'
                                             improvements or incurred in
                                             renovating or otherwise improving,
                                             decorating, painting or
                                             redecorating vacant space for
                                             tenants or other occupants of the
                                             Building;

                                    (xiii)   expenses in connection with
                                             services or other benefits which
                                             are offered to other tenants of the
                                             Building or Complex but not to
                                             Tenant or for which Tenant is
                                             charged directly, other than
                                             through Operating Costs;

                                    (xiv)    fines, interest and penalties
                                             incurred by Landlord due to the
                                             violation by Landlord or any tenant
                                             of the terms and conditions of any
                                             lease of space in the Building;

                                    (xv)     management fees paid or charged by
                                             Landlord in connection with the
                                             management of the Building to the
                                             extent such management fee is in
                                             excess of the market rate.

                                    (xvi)    salaries and other benefits paid to
                                             any executive employees above the
                                             level of senior property manager of
                                             the Complex;

                                    (xvii)   amounts paid to Landlord or to
                                             subsidiaries or affiliates of
                                             Landlord for goods and/or services
                                             in the Building to the extent the
                                             same exceeds the costs of such
                                             goods and/or services rendered by
                                             unaffiliated third parties on a
                                             competitive basis;

                                    (xviii)  landlord's general corporate
                                             overhead and general administrative
                                             expenses;

                                    (xix)    any compensation paid to clerks,
                                             attendants or other persons in
                                             commercial concessions operated by
                                             Landlord;


                                      -15-
<PAGE>   25
                                    (xx)     services provided, taxes,
                                             attributable to, and costs incurred
                                             in connection with the operation
                                             (as opposed to the repair and
                                             maintenance thereof which shall be
                                             included in Operating Costs) of any
                                             garage for the Building, and any
                                             replacement garages or parking
                                             facilities;

                                    (xxi)    costs incurred in connection with
                                             upgrading the Building to comply
                                             with laws, rules, regulations and
                                             codes in effect prior to the Term
                                             Commencement Date;

                                    (xxii)   fines, interest and penalties
                                             arising from the negligence or
                                             willful misconduct of Landlord or
                                             other tenants or occupants of the
                                             Building or their respective
                                             agents, employees, licensees,
                                             vendors, contractors or providers
                                             of materials or services;

                                    (xxiii)  costs arising from Landlord's
                                             political contributions;

                                    (xxiv)   costs for sculpture, paintings or
                                             other objects of art;

                                    (xxv)    costs associated with the operation
                                             of the business of the entity which
                                             constitutes Landlord as the same
                                             are distinguished from the costs of
                                             operation of the Building,
                                             including accounting and legal
                                             matters, costs of defending any
                                             lawsuits with any mortgagee (except
                                             as the actions of Tenant may be in
                                             issue), costs of selling,
                                             syndicating, financing, mortgaging
                                             or hypothecating any of Landlord's
                                             interest in the Building, costs
                                             incurred in connection with any
                                             disputes between Landlord and its
                                             employees, between Landlord and
                                             Building management, or between
                                             Landlord and other tenants or
                                             occupants;

                                    (xxvi)   rentals for items which, if
                                             purchased rather than rented, would
                                             constitute a capital cost, to the
                                             extent that the rental payments
                                             exceed the costs which could be
                                             included pursuant to paragraph (g5)
                                             below;

                                    (xxvii)  costs of electricity for plugs and
                                             lights provided to other tenants'
                                             demised premises;

                                    (xxviii) Repair and replacement costs in
                                             connection with defects in
                                             Landlord's Work which are incurred
                                             by Landlord prior to the third
                                             (3rd) anniversary of the Term
                                             Commencement Date in respect of
                                             Portion A; and

                                    (xxix)   any costs related to any
                                             development, demolition or
                                             construction activity in the
                                             Building or the Complex, including,
                                             without limitation, in connection
                                             with the demolition and development
                                             of Building 549 and any and all
                                             costs of construction mitigation
                                             measures, including, without
                                             limitation, dust control, cleaning,
                                             maintenance, debris removal,
                                             traffic control and noise control,
                                             but the foregoing

                                      -16-
<PAGE>   26
                                             shall have no effect on the
                                             inclusion of the cost of normal
                                             cleaning services for the Complex.

                           (g5) Capital Expenditures.

                                    (i) Replacements. If, during the term of
                 this Lease, Landlord shall replace any capital items or make
                 any capital expenditures (collectively called "Capital
                 Expenditures") the total amount of which is not properly
                 includable in Operating Costs for the Operating Year in which
                 they were made, in accordance with generally accepted
                 accounting principles and practices in effect at the time of
                 such replacement, there shall nevertheless be included in such
                 Operating Costs and in Operating Costs for each succeeding
                 Operating Year the amount, if any, by which the Annual
                 Charge-Off (determined as hereinafter provided) of such Capital
                 Expenditure (less insurance proceeds, if any, collected by
                 Landlord by reason of damage to, or destruction of the capital
                 item being replaced) exceeds the Annual Charge-Off of the
                 Capital Expenditure for the item being replaced.

                                    (ii) New Capital Items. If a new capital
                 item is acquired which does not replace another capital item
                 which was worn out, has become obsolete, etc., and such new
                 capital item being acquired is either (i) required by law or
                 (ii) reasonably projected to reduce Operating Costs, then there
                 shall be included in Operating Costs for each Operating Year in
                 which and after such capital expenditure is made the Annual
                 Charge-Off of such capital expenditure.

                                    (iii) Annual Charge-Off. "Annual Charge-Off"
                 shall be defined as the annual amount of principal and interest
                 payments which would be required to repay a loan ("Capital
                 Loan") in equal monthly installments over the Useful Life, as
                 hereinafter defined, of the capital item in question on a
                 direct reduction basis at an annual interest rate equal to the
                 Capital Interest Rate, as hereinafter defined, where the
                 initial principal balance is the cost of the capital item in
                 question.

                                    (iv) Useful Life. "Useful Life" shall be
                 reasonably determined by Landlord in accordance with generally
                 accepted accounting principles and practices in effect at the
                 time of acquisition of the capital item. Notwithstanding the
                 foregoing, if Landlord reasonably concludes on the basis of
                 engineering estimates that a particular capital expenditure
                 will effect savings in Complex operating expenses including,
                 without limitation, energy-related costs, and that such annual
                 projected savings will exceed the Annual Charge-Off of Capital
                 Expenditures computed as aforesaid, then and in such events,
                 the Annual Charge-Off shall be determined based upon a Useful
                 Life which would cause the principal and interest payments in a
                 full repayment of the Capital Loan in question to equal the
                 amount of projected savings of such Useful Life.

                                    (v) Capital Interest Rate. "Capital Interest
                 Rate" shall be defined as an annual rate of either one
                 percentage point over the AA Bond rate (Standard & Poor's
                 corporate composite or, if unavailable, its equivalent) as
                 reported in the financial press at the time the capital
                 expenditure is made or, if the capital item is acquired through
                 third-party financing, then the actual (including fluctuating)
                 rate paid by Landlord in financing the acquisition of such
                 capital item.

                           (g6) Specifically Included Categories of Operating
         Costs. Subject to the Excluded Costs definition, the qualifications on
         reimbursable Building Operating Costs and Complex Operating Costs set
         forth in Articles 9.1(g1) 9.1(g2) and 9.1(g3), and except as otherwise
         expressly excluded from the definition of Building Operating Costs and
         Complex Operating Costs pursuant to the provisions of this Lease,
         Building Operating Costs and Complex

                                      -17-
<PAGE>   27
         Operating Costs shall include, but not be limited to, the following,
         provided that if such costs are attributable to the Building and to
         other buildings in the Complex, then such costs shall be equitably
         apportioned among the Building and such other buildings in accordance
         with Article 9.1(g3), and if such costs are attributable to common
         areas of the Complex and to other property which is not part of the
         Complex, then such costs shall be equitably apportioned among the
         Complex and such other property.

         Real Estate Taxes: Land Taxes only, and not Building Taxes, as such
         terms are defined in Article 9.1(d).

         Taxes (other than real estate taxes): Sales taxes and Federal Social
         Security, Unemployment and Old Age Taxes and contributions and State
         Unemployment taxes and contributions accruing to and paid by the
         Landlord on account of all employees of Landlord and/or Landlord's
         managing agent, who are employed in, about or on account of the
         Premises (to the extent that the underlying wages or salaries are
         included in Building Operating Costs or Complex Operating Costs, as the
         case may be), except that taxes levied upon the net income of the
         Landlord and taxes withheld from employees, and "Taxes" as defined in
         Article 9.1(d) shall not be included herein.

         Water: All charges and rates connected with water supplied to the
         Premises, the Building and/or the common areas of the Complex and
         related sewer use charges.

         Heat and Air Conditioning: All charges connected with heat and air
         conditioning supplied to the Premises, Building and/or Complex.

         Wages: Wages and cost of all employee benefits of all employees of the
         Landlord and/or Landlord's managing agent who are employed in, about or
         on account of the Premises and/or Complex provided that wages and costs
         for employees who also work on other properties shall be allocated to
         the Complex based upon the proportion of their time spent working on
         the Complex and then allocated to the Premises on a square foot basis.

         Cleaning: The cost of labor and material for cleaning the Premises
         and/or Complex, surrounding areaways and windows in the Premises and/or
         Complex, including, without limitation, the services listed on Exhibit
         4.

         Elevator Maintenance: All expenses for or on account of the upkeep and
         maintenance of all elevators in the Premises, Building and/or the
         Complex (if any).

         Electricity: The cost of all electric current for the operation of any
         machine, appliance or device used for the operation of the Premises and
         the Building and/or Complex, including the cost of electric current for
         the elevators, lights, air conditioning and heating, but not including
         electric current which is paid for directly to the utility by the
         user/tenant in the Premises and/or Complex. (If and so long as Tenant
         is billed directly by the electric utility for its own consumption of
         electricity for lights and plugs as determined by its separate meter or
         by submeter, then Operating Costs shall include only public area
         electric current consumption and electricity for base building HVAC and
         not any demised Premises electric current consumption for lights and
         plugs.) Wherever separate metering is unlawful, prohibited by utility
         company regulation or tariff or is otherwise impracticable, relevant
         consumption figures for the purposes of this Article 9 shall be
         determined by fair and reasonable allocations and engineering estimates
         made by Landlord.

         Insurance, etc.: Fire, casualty, liability and such other insurance as
         may from time to time be reasonably required by lending institutions on
         first-class office buildings in the City or Town

                                      -18-
<PAGE>   28
         wherein the Building is located and all other expenses customarily
         incurred in connection with the operation and maintenance of
         first-class suburban office/research and development buildings in the
         Market Area.

         Management Space: Market rate rental costs associated with the
         Complex's management office.

         Complex Amenities: The cost of operating any amenities in the Complex
         available to all tenants of the Complex including, without limitation,
         any cafeteria. The costs to be included in Complex Operating Costs
         shall include any subsidy, including lower than market rate rent,
         provided by Landlord for or with respect to such amenity. In the event
         that the costs of a Complex amenity are included in an Operating Year
         but such costs were not included in the Complex Operating Costs Base,
         then the Complex Operating Costs Base shall be adjusted to reflect what
         would have been the costs for such amenity in the Complex Operating
         Costs Base if such amenity had been operated during calendar year 2000.

         9.2 TAX EXCESS.

                  (a) In General. Commencing as of the Term Commencement Date in
respect of each Portion of the Premises, and continuing thereafter throughout
the term of this Lease in respect of such Portion of the Premises, if in any Tax
Period the Building Taxes exceed the Building Tax Base, Tenant shall pay to
Landlord Tenant's Building Tax Percentage in respect of each Portion of the
Premises of such excess, such amount being hereinafter referred to as "Tax
Excess." Tax Excess shall be due within thirty (30) days of Tenant's receipt of
Landlord's bill therefor. In implementation and not in limitation of the
foregoing, Tenant shall remit to Landlord pro rata monthly installments on
account of projected Tax Excess, calculated by Landlord on the basis of the most
recent Tax data available. If the total of such monthly remittances on account
of any Tax Period is greater than the actual Tax Excess for such Tax Period,
Tenant may credit the difference against the next installment of rental or other
charges due to Landlord hereunder, except that if such difference is determined
after the end of the term of this Lease, Landlord shall refund such difference
to Tenant within thirty (30) days after such determination to the extent that
such difference exceeds any amounts then due from Tenant to Landlord. If the
total of such remittances is less than the actual Tax Excess for such Tax
Period, Tenant shall pay the difference to Landlord within thirty (30) days of
Tenant's receipt of the bill.

                  (b) Effect of Abatements. Appropriate credit against Tax
Excess shall be given for any refund obtained by reason of a reduction in any
Taxes by the Assessors or the administrative, judicial or other governmental
agency responsible therefor. The original computations, as well as reimbursement
or payments of additional charges, if any, or allowances, if any, under the
provisions of this Article 9.2 shall be based on the original assessed
valuations with adjustments to be made at a later date when the tax refund, if
any, shall be paid to Landlord by the taxing authorities. Expenditures for
reasonable legal fees and for other reasonable similar or dissimilar expenses
incurred in obtaining the tax refund may be charged against the tax refund
before the adjustments are made for the Tax Period.

         9.3 OPERATING EXPENSE EXCESS.

         Commencing as of the Term Commencement Date in respect of each Portion
of the Premises, and continuing thereafter throughout the term of the Lease in
respect of such Portion of the Premises, if the Building Operating Costs in any
Operating Year exceed the Building Operating Cost Base, or if the Complex
Operating Costs in any Operating Year exceed the Complex Operating Cost Base,
Tenant shall pay to Landlord Tenant's Building or Complex Operating Cost
Percentage, respectively, in respect of each Portion of the Premises of such
excess, such amounts being hereinafter collectively referred to as "Operating
Expense Excess." Operating Expense Excess shall be due within thirty (30) days
of the Tenant's receipt of the Landlord's bill therefor. In implementation and
not in limitation of the foregoing, Tenant shall remit to Landlord pro rata
monthly installments on account of projected Operating Expense

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<PAGE>   29
Excess, calculated by Landlord on the basis of the most recent Operating Costs
data or budget available. Landlord shall, within one hundred twenty (120) days
after the end of each Operating Year, deliver to Tenant a reasonably detailed
statement ("Year End Statement") of the actual amount of Operating Costs for
such Operating Year. If the total of such monthly remittances on account of any
Operating Year is greater than the actual Operating Expense Excess for such
Operating Year, Tenant may credit the difference against the next installment of
rent or other charges due to Landlord hereunder, except that if such difference
is determined after the end of the term of this Lease, Landlord shall refund
such difference to Tenant within thirty (30) days after such determination to
the extent that such difference exceeds any amounts then due from Tenant to
Landlord. If the total of such remittances is less than actual Operating Expense
Excess for such Operating Year, Tenant shall pay the difference to Landlord
within thirty (30) days of Tenant's receipt of Landlord's bill therefor.

         9.4 PART YEARS. If any Term Commencement Date or if the Termination
Date occurs in the middle of an Operating Year or Tax Period, Tenant shall be
liable for only that portion of the Operating Expense or Tax Excess, as the case
may be, in respect of such Operating Year or Tax Period represented by a
fraction the numerator of which is the number of days of the herein term
(commencing as of the applicable Term Commencement Date) which falls within the
Operating Year or Tax Period and the denominator of which is three hundred
sixty-five (365), or the number of days in said Tax Period, as the case may be.

         9.5 EFFECT OF TAKING. In the event of any taking of a portion of the
Complex, the Building or the land upon which it stands under circumstances
whereby this Lease shall not terminate under the provisions of Article 20 then,
for the purposes of determining Tax Excess, there shall be substituted for the
Tax Base originally provided for herein a fraction of such Tax Base, the
numerator of which fraction shall be the Taxes for the first Tax Period
subsequent to the condemnation or taking which takes into account such
condemnation or taking, and the denominator of which shall be the Taxes for the
last Tax Period prior to the condemnation or taking, which did not take into
account such condemnation or taking. Tenant's Building Tax Percentage shall be
adjusted appropriately to reflect the proportion of the Premises, the Building
and/or the Complex remaining after such taking.

          9.6 ADJUSTMENT OF OPERATING COSTS BASED UPON OCCUPANCY. If less than
ninety-five percent (95%) of the rentable area of the Building shall have been
occupied by tenants at any time during any Operating Year (including the Base
Year), or if services, for any other reason, are not provided by Landlord to at
least ninety-five (95%) percent of the rentable area of the Building, then, at
Landlord's election, Building Operating Costs for such Operating Year shall be
adjusted to equal the amount which Landlord reasonably determines is the amount
Building Operating Costs would have been for such period had occupancy been
ninety-five percent (95%) throughout such period, or if such services had been
provided to ninety-five (95%) percent of the Building throughout such period, as
the case may be.

         9.7 DISPUTES, ETC. Any disputes arising under this Article 9 may, at
the election of either party, be submitted to arbitration as hereinafter
provided. Any obligations under this Article 9 which shall not have been paid at
the expiration or sooner termination of the term of this Lease shall survive
such expiration and shall be paid when and as the amount of same shall be
determined and be due.

         9.8 TENANT'S AUDIT RIGHTS. Subject to the provisions of this paragraph,
Tenant shall have the right, at Tenant's cost and expense, to examine all
documentation and calculations prepared in the determination of Operating
Expense Excess:

                  1.       Such documentation and calculation shall be made
                           available to Tenant at the offices where Landlord
                           keeps such records during normal business hours
                           within a reasonable time after Landlord receives a
                           written request from Tenant to make such examination.


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<PAGE>   30
                  2.       Tenant shall have the right to make such examination
                           no more than once in respect of any period in which
                           Landlord has given Tenant a statement of the actual
                           amount of Operating Costs.

                  3.       Any request for examination in respect of any
                           Operating Year may be made no more than sixty (60)
                           days after Landlord advises Tenant of the actual
                           amount of Operating Costs in respect of such period.

                  4.       Such examination may be made only by a nationally
                           recognized independent certified public accounting
                           firm approved by Landlord, such approval not to be
                           unreasonably withheld or delayed. Without limiting
                           Landlord's approval rights, Landlord may withhold its
                           approval of any examiner of Tenant who is being paid
                           by Tenant on a contingent fee basis.

                  5.       As a condition to performing any such examination,
                           Tenant and its examiners shall be required to execute
                           and deliver to Landlord an agreement, in form
                           reasonably acceptable to Landlord, agreeing to keep
                           confidential any information which it discovers about
                           Landlord or the Building or the Complex in connection
                           with such examination.

                  6.       If such audit reveals an overcharge of more than five
                           percent (5%), Landlord shall reimburse Tenant the
                           reasonable cost of such audit within thirty (30) days
                           after written demand therefor.

10.      CHANGES OR ALTERATIONS BY LANDLORD

         Landlord reserves the right, exercisable by itself or its nominee, at
any time and from time to time without the same constituting an actual or
constructive eviction and without incurring any liability to Tenant therefor or
otherwise affecting Tenant's obligations under this Lease, to make such changes,
alterations, additions, improvements, repairs or replacements in or to the
Building (including the Premises) and the fixtures and equipment thereof, as
well as in or to the street entrances, halls, passages, elevators, escalators,
and stairways thereof, as it may deem necessary or desirable, and to change the
arrangement and/or location of entrances or passageways, doors and doorways, and
corridors, elevators, stairs, toilets, or other public parts of the Building,
provided, however, that there be no unreasonable obstruction of the right of
access to, or unreasonable interference with the use and enjoyment of, the
Premises by Tenant. Nothing contained in this Article 10 shall be deemed to
relieve Tenant of any duty, obligation or liability of Tenant with respect to
making any repair, replacement or improvement or complying with any law, order
or requirement of any governmental or other authority. Landlord reserves the
right to adopt and at any time and from time to time to change the name or
address of the Building. After the initial change of the name and address of the
Building, Landlord shall provide to Tenant at least six (6) months' prior
written notice of any subsequent change of the name or address of the Building.
Neither this Lease nor any use