Document:

<PAGE>   1
                                                                   EXHIBIT 10.26

                               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

                                      -19-
<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.

                                      -20-
<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 by Tenant shall give Tenant any right or easement
for the use of any door or any passage or any concourse connecting with any
other building or to any public convenience, and the use of such doors, passages
and concourses and of such conveniences may be regulated or discontinued at any
time and from time to time by Landlord without notice to Tenant and without
affecting the obligation of Tenant hereunder or incurring any liability to
Tenant therefor, provided, however, that there be no unreasonable obstruction of
the right of access to, or unreasonable interference with the use of the
Premises by Tenant.

         If at any time any windows of the Premises are temporarily closed or
darkened for any reason whatsoever including but not limited to, Landlord's own
acts, Landlord shall not be liable for any damage Tenant may sustain thereby and
Tenant shall not be entitled to any compensation therefor nor abatements of rent
nor shall the same release Tenant from its obligations hereunder nor constitute
an eviction.

                                      -21-
<PAGE>   31
         Subject to the provisions of Article 8.8(b) hereof, during the
performance of demolition or renovation of existing buildings and construction
of new buildings by Landlord in the Complex, Landlord, its agents, employees and
contractors shall use reasonable efforts to minimize any interference with
Tenant's use and occupancy of the Premises.

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

         All fixtures, equipment, improvements and appurtenances attached to or
built into the Premises prior to or during the term, whether by Landlord at its
expense or at the expense of Tenant (either or both) or by Tenant shall be and
remain part of the Premises and shall not be removed by Tenant during or at the
end of the term unless Landlord otherwise elects to require Tenant to remove
such fixtures, equipment, improvements and appurtenances, in accordance with
Articles 12 and/or 22 of the Lease; provided, however, that Tenant shall have
the right to remove (at Tenant's expense) the items of Tenant's Removable
Property listed on Exhibit 8, attached hereto, provided that such removal shall
not materially damage the Premises or the Building and that the cost of
repairing any damage to the Premises or the Building arising from installation
or such removal shall be paid by Tenant. All electric, plumbing, heating and
sprinkling systems, fixtures and outlets, vaults, paneling, molding, shelving,
radiator enclosures, cork, rubber, linoleum and composition floors, ventilating,
silencing, air conditioning and cooling equipment, shall be deemed to be
included in such fixtures, equipment, improvements and appurtenances, whether or
not attached to or built into the Premises. Where not built into the Premises,
all removable electric fixtures, carpets, drinking or tap water facilities,
furniture, or trade fixtures or business equipment or Tenant's inventory or
stock in trade shall not be deemed to be included in such fixtures, equipment,
improvements and appurtenances and may be, and upon the request of Landlord will
be, removed by Tenant upon the condition that such removal shall not materially
damage the Premises or the Building and that the cost of repairing any damage to
the Premises or the Building arising from installation or such removal shall be
paid by Tenant. If this Lease shall be terminated by reason of Tenant's breach
or default, then, notwithstanding anything to the contrary in this Lease
contained, Landlord shall have a lien against all Tenant's property in the
Premises or elsewhere in the Building at the time of such termination to secure
Landlord's rights under Article 21 hereof. Tenant shall, within ten (10) days of
Landlord's written request, from time to time, execute and deliver to Landlord
such documentation (e.g., UCC statements) as may be necessary to enable Landlord
to perfect such lien.

12.      ALTERATIONS AND IMPROVEMENTS BY TENANT

         Tenant shall make no alterations, decorations, installations, removals,
additions or improvements in or to the Premises without Landlord's prior written
consent and then only those (i) which equal or exceed the specifications and
quantities provided in Exhibit 3 and (ii) made by contractors or mechanics
approved by Landlord. No installations or work shall be undertaken or begun by
Tenant until: (i) Landlord has approved written plans and specifications and a
time schedule for such work; (ii) Tenant has made provision for either written
waivers of liens from all contractors, laborers and suppliers of materials for
such installations or work, the filing of lien bonds on behalf of such
contractors, laborers and suppliers, or other appropriate protective measures
approved by Landlord and reasonably and customarily required by other landlords
of first class office buildings in Cambridge, Massachusetts for work of the type
being performed; and (iii) where the cost of such work exceeds $300,000.00 in
any one instance, Tenant has procured appropriate surety payment and performance
bonds. No amendments or additions to such plans and specifications shall be made
without the prior written consent of Landlord. Landlord's consent and approval
required under this Article 12 shall not be unreasonably withheld. 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 the Premises and the placement of
Tenant's furniture, appliances and equipment), and Landlord's approval of

                                      -22-
<PAGE>   32
Tenant's plans shall in no event relieve Tenant of the responsibility for such
design. Landlord shall have no liability or responsibility for any claim, injury
or damage alleged to have been caused by the particular materials, whether
building standard or non-building standard, appliances or equipment selected by
Tenant in connection with any work performed by or on behalf of Tenant in the
Premises including, without limitation, furniture, carpeting, copiers, laser
printers, computers and refrigerators. Any such work, alterations, decorations,
installations, removals, additions and improvements shall be done at Tenant's
sole expense and at such times and in such manner as Landlord may from time to
time designate. If Tenant shall make any alterations, decorations,
installations, removals, additions or improvements to either Portion of the
Premises, then Landlord may elect to require the Tenant at the expiration or
sooner termination of the term of this Lease to restore the Premises to
substantially the same condition as existed at the Term Commencement Date in
respect of such Portion of the Premises. Landlord agrees to make such election
at the time that Landlord approves Tenant's plans for any such alterations,
etc., if Tenant requests in writing that Landlord make such election at the time
that Tenant requests Landlord's approval of such alterations, etc.

         Tenant shall have the right, during the term of the Lease, to use the
internal stairwells of the Building to provide access for Tenant's employees
between the floors of the Premises provided that (i) such use is permitted by
applicable law, (ii) Landlord shall, if required by applicable laws, rules,
orders and regulations, install a card key access system for the doors to and
from such stairwells, and (iii) Tenant shall reimburse Landlord, as additional
rent, or shall use a portion of the Landlord Allowance, for the costs incurred
by Landlord to install such card key access system.

         Notwithstanding anything to the contrary herein contained, Tenant shall
have the right, without obtaining Landlord's consent, to make interior
nonstructural alterations, additions, or improvements, provided however that
Tenant:

                  (i)      shall give prior written notice to Landlord of such
                           alterations, additions or improvements;

                  (ii)     Tenant shall submit to Landlord plans for such
                           alterations, additions or improvements if Tenant
                           utilizes plans for such alterations, additions or
                           improvements, and

                  (iii)    that such alterations, additions or improvements
                           shall not materially, adversely affect any of the
                           Building's systems, or the ceiling of the Premises.

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

         Whenever Tenant shall make any alterations, decorations, installations,
removals, additions or improvements in or to either Portion of the
Premises--whether such work be done prior to or after the Term Commencement Date
in respect to such Portion of the Premises--Tenant will strictly observe the
following covenants and agreements:

                  (a) Tenant agrees that it will not, either directly or
indirectly, use any contractors and/or materials if their use will create any
difficulty, whether in the nature of a labor dispute or otherwise, with other
contractors and/or labor engaged by Tenant or Landlord or others in the
construction, maintenance and/or operation of the Building or any part thereof.

                  (b) In no event shall any material or equipment be
incorporated in or added to the Premises, so as to become a fixture or otherwise
a part of the Building, in connection with any such alteration, decoration,
installation, addition or improvement which is subject to any lien, charge,
mortgage or other encumbrance of any kind whatsoever or is subject to any
security interest or any form of title

                                      -23-
<PAGE>   33
retention agreement. No installations or work shall be undertaken or begun by
Tenant until (i) Tenant has made provision for written waiver of liens from all
contractors, laborers and suppliers of materials for such installations or work,
and taken other appropriate protective measures approved by Landlord; and (ii)
Tenant has procured appropriate surety payment and performance bonds which shall
name Landlord as an additional obligee and has filed lien bond(s) (in
jurisdictions where available) on behalf of such contractors, laborers and
suppliers. Any mechanic's lien filed against the Premises or the Building for
work claimed to have been done for, or materials claimed to have been furnished
to, Tenant shall be discharged by Tenant within ten (10) days thereafter, at
Tenant's expense by filing the bond required by law or otherwise. If Tenant
fails so to discharge any lien, Landlord may do so at Tenant's expense and
Tenant shall reimburse Landlord for any expense or cost incurred by Landlord in
so doing within fifteen (15) days after rendition of a bill therefor.
Notwithstanding the foregoing, Tenant shall have the right to grant security
interests and/or to lease its business equipment and personal property in the
Premises which were not paid for in whole or in part by the Landlord Allowance,
provided that such lessor or secured party agrees:

                           1.       That it will repair any damage to the
                                    Building or the Premises caused by the
                                    installation or removal of any such
                                    equipment or personal property;

                           2.       That it will give Landlord not less than
                                    five (5) days advance written notice prior
                                    to making any entry into the Premises;

                           3.       That it will not hold any auction or
                                    foreclosure sale on the Premises; and

                           4.       That it will have the right to remove such
                                    equipment or property only during the term
                                    of this Lease.

                  (c) All installations or work done by Tenant shall be at its
own expense and shall at all times comply with (i) laws, rules, orders and
regulations of governmental authorities having jurisdiction thereof; (ii)
orders, rules and regulations of any Board of Fire Underwriters, or any other
body hereafter constituted exercising similar functions, and governing insurance
rating bureaus; (iii) Rules and Regulations of Landlord; and (iv) plans and
specifications prepared by and at the expense of Tenant theretofore submitted to
and approved by Landlord. Notwithstanding any other provision of this Lease,
Tenant shall not be responsible for compliance with any laws, regulations, or
the like requiring (i) structural repairs or modifications or (ii) repairs or
modifications to the utility or building service equipment or (iii) installation
of new building service equipment, such as fire detection or suppression
equipment, unless such repairs, modifications, or installations shall be (a) due
to Tenant's particular use or manner of use of the Premises (as opposed to
office use generally), (b) due to the negligence or willful misconduct of Tenant
or any agent, employee, or contractor of Tenant, or (c) due to alterations,
additions or installations by or on behalf of Tenant.

                  (d) Tenant shall procure all necessary permits before
undertaking any work in the Premises; do all of such work in a good and
workmanlike manner, employing materials of good quality and complying with all
governmental requirements; and defend, save harmless, exonerate and indemnify
Landlord from all injury, loss or damage to any person or property occasioned by
or growing out of such work. Tenant shall cause contractors employed by Tenant
to carry Worker's Compensation Insurance in accordance with statutory
requirements, Automobile Liability Insurance and, naming Landlord as an
additional insured, Commercial General Liability Insurance covering such
contractors on or about the Premises in the amounts stated in Article 15 hereof
or in such other reasonable amounts as Landlord shall require and to submit
certificates evidencing such coverage to Landlord prior to the commencement of
such work.

                                      -24-
<PAGE>   34
14.      REPAIRS BY TENANT--FLOOR LOAD

         14.1 REPAIRS BY TENANT. Tenant shall keep all and singular each Portion
of the Premises neat and clean (including periodic rug shampoo and waxing of
tiled floors and cleaning of blinds and drapes) and in such repair, order and
condition as the same are in on the Term Commencement Date in respect of such
Portion of the Premises or may be put in during the term hereof, reasonable use
and wearing thereof and damage by fire or by other casualty excepted. Tenant
shall be solely responsible for the proper maintenance of all equipment and
appliances operated by Tenant, including, without limitation, copiers, laser
printers, computers and refrigerators. Tenant shall make, as and when needed as
a result of misuse by, or neglect or improper conduct of, Tenant or Tenant's
servants, employees, agents, contractors, invitees, or licensees or otherwise,
all repairs in and about the Premises necessary to preserve them in such repair,
order and condition, which repairs shall be in quality and class equal to the
original work. Landlord may elect, at the expense of Tenant, to make any such
repairs or to repair any damage or injury to the Building or the Premises caused
by moving property of Tenant in or out of the Building, or by installation or
removal of furniture or other property, or by misuse by, or neglect, or improper
conduct of, Tenant or Tenant's servants, employees, agents, contractors, or
licensees.

         14.2 FLOOR LOAD--HEAVY MACHINERY. Tenant shall not place a load upon
any floor of the Premises exceeding the floor load per square foot of area which
such floor was designed to carry and which is allowed by law. Landlord reserves
the right to prescribe the weight and position of all business machines and
mechanical equipment, including safes, which shall be placed so as to distribute
the weight. Business machines and mechanical equipment shall be placed and
maintained by Tenant at Tenant's expense in settings sufficient in Landlord's
judgment to absorb and prevent vibration, noise and annoyance. Tenant shall not
move any safe, heavy machinery, heavy equipment, freight, bulky matter, or
fixtures into or out of the Building without Landlord's prior written consent.
If such safe, machinery, equipment, freight, bulky matter or fixtures requires
special handling, Tenant agrees to employ only persons holding a Master Rigger's
License to do said work, and that all work in connection therewith shall comply
with applicable laws and regulations. Any such moving shall be at the sole risk
and hazard of Tenant and Tenant will defend, indemnify and save Landlord
harmless against and from any liability, loss, injury, claim or suit resulting
directly or indirectly from such moving. Proper placement of all such business
machines, etc., in the Premises shall be Tenant's responsibility.

15.      INSURANCE, INDEMNIFICATION, EXONERATION AND EXCULPATION

         15.1 GENERAL LIABILITY INSURANCE. Tenant shall procure, and keep in
force and pay for Commercial General Liability Insurance insuring Tenant on an
occurrence basis against all claims and demands for personal injury liability
(including, without limitation, bodily injury, sickness, disease, and death) or
damage to property which may be claimed to have occurred from and after the time
Tenant and/or its contractors enter the Premises in accordance with Article 4 of
this Lease, of not less than Two Million ($2,000,000) Dollars in the event of
personal injury to any number of persons or damage to property, arising out of
any one occurrence, and from time to time thereafter shall be not less than such
higher amounts, if procurable, as may be reasonably required by Landlord and are
customarily carried by responsible similar tenants in the City or Town wherein
the Building is located.

         15.2 CERTIFICATES OF INSURANCE. Such insurance shall be effected with
insurers approved by Landlord, authorized to do business in the State wherein
the Building is situated under valid and enforceable policies wherein Tenant
names Landlord and Landlord's managing agent as additional insureds. Such
insurance shall provide that it shall not be canceled or modified without at
least thirty (30) days' prior written notice to each insured named therein. On
or before the time Tenant and/or its contractors enter the Premises in
accordance with Articles 4 and 14 of this Lease and thereafter not less than
fifteen (15) days prior to the expiration date of each expiring policy, original
copies of the policies provided for in Article 15.1 issued by the respective
insurers, or certificates of such policies setting forth in full the provisions
thereof and issued by such insurers together with evidence satisfactory to
Landlord of

                                      -25-
<PAGE>   35
the payment of all premiums for such policies, shall be delivered by Tenant to
Landlord and certificates as aforesaid of such policies shall upon request of
Landlord, be delivered by Tenant to the holder of any mortgage affecting the
Premises.

         15.3 GENERAL. Tenant will save Landlord, its agents and employees,
harmless and will exonerate, defend and indemnify Landlord, its agents and
employees, from and against any and all claims, liabilities or penalties
asserted by or on behalf of any person, firm, corporation or public authority
arising from the Tenant's breach of the Lease or:

                  (a) On account of or based upon any injury to person, or loss
of or damage to property, sustained or occurring on the Premises on account of
or based upon the act, omission, fault, negligence or misconduct of any person
whomsoever (except to the extent the same is caused by Landlord, its agents,
contractors or employees);

                  (b) On account of or based upon any injury to person, or loss
of or damage to property, sustained or occurring elsewhere (other than on the
Premises) in or about the Building (and, in particular, without limiting the
generality of the foregoing, on or about the elevators, stairways, public
corridors, sidewalks, concourses, arcades, malls, galleries, vehicular tunnels,
approaches, areaways, roof, or other appurtenances and facilities used in
connection with the Building or Premises) to the extent arising out of the use
or occupancy of the Building or Premises by the Tenant, or by any person
claiming by, through or under Tenant, to the extent on account of or based upon
the fault, negligence or misconduct of Tenant, its agents, employees or
contractors; and

                  (c) On account of or based upon (including monies due on
account of) any work or thing whatsoever done (other than by Landlord or its
contractors, or agents or employees of either) on either Portion of the Premises
during the term of this Lease and during the period of time, if any, prior to
the Term Commencement Date in respect of such Portion of the Premises that
Tenant may have been given access to such Portion of the Premises.

                  (d) Tenant's obligations under this Article 15.3 shall be
insured either under the Commercial General Liability Insurance required under
Article 15.1, above, or by a contractual insurance rider or other coverage; and
certificates of insurance in respect thereof shall be provided by Tenant to
Landlord upon request.

                  (e) Except as set forth in this Article 15.3(e), Tenant shall
not be liable to Landlord for consequential damages. Notwithstanding the
foregoing, in the event that Tenant is required to indemnify Landlord against
the claim of a third party pursuant to this Article 15.3, and if such third
party recovers a judgment against Landlord for consequential damages based upon
the negligence or willful misconduct of Tenant, its contractors, agents or
employees, Tenant shall be liable for such consequential damages suffered by
such third party. The foregoing shall not limit Landlord's right to recover
damages in accordance with Article 21.3 (x) or (y) or to recover damages in
accordance with the last paragraph of Article 22 as the result of a holdover by
Tenant in the premises beyond the term of the Lease.

         15.4 PROPERTY OF TENANT. In addition to and not in limitation of the
foregoing, Tenant covenants and agrees that, to the maximum extent permitted by
law, all merchandise, furniture, fixtures and property of every kind, nature and
description related or arising out of Tenant's leasehold estate hereunder, which
may be in or upon the Premises or Building, in the public corridors, or on the
sidewalks, areaways and approaches adjacent thereto, shall be at the sole risk
and hazard of Tenant, and that if the whole or any part thereof shall be
damaged, destroyed, stolen or removed from any cause or reason whatsoever no
part of said damage or loss shall be charged to, or borne by, Landlord, except,
subject to Article 19 hereof, to the extent such damage or loss is due to the
negligence or willful misconduct of Landlord or Landlord's agents, employees or
contractors, in which case Landlord shall bear loss or damage only to "ordinary
office property" (as hereinafter defined). For the purpose of this Article 15.4,

                                      -26-
<PAGE>   36
"ordinary office property" shall mean merchandise, furniture, and other tangible
personal property of the kind and quantity which may customarily be expected to
be found within comparable business offices in the greater Cambridge area, and
excluding any unusually valuable or exotic property, works of art, and the like.

         15.5 BURSTING OF PIPES, ETC. Landlord shall not be liable for any
injury or damage to persons or property resulting from fire, explosion, falling
plaster, steam, gas, air contaminants or emissions, electricity, electrical or
electronic emanations or disturbance, water, rain or snow or leaks from any part
of the Building or from the pipes, appliances, equipment or plumbing works or
from the roof, street or sub-surface or from any other place or caused by
dampness, vandalism, malicious mischief or by any other cause of whatever
nature, unless caused by or due to the negligence of Landlord, its agents,
servants or employees, and then, where notice and an opportunity to cure are
appropriate (i.e., where Tenant has an opportunity to know or should have known
of such condition sufficiently in advance of the occurrence of any such injury
or damage resulting therefrom as would have enabled Landlord to prevent such
damage or loss had Tenant notified Landlord of such condition) only after (i)
notice to Landlord of the condition claimed to constitute negligence and (ii)
the expiration of a reasonable time after such notice has been received by
Landlord without Landlord having taken all reasonable and practicable means to
cure or correct such condition; and pending such cure or correction by Landlord,
Tenant shall take all reasonably prudent temporary measures and safeguards to
prevent any injury, loss or damage to persons or property. In no event shall
Landlord be liable for any loss, the risk of which is covered by Tenant's
insurance or is required to be so covered by this Lease; nor shall Landlord or
its agents be liable for any such damage caused by other tenants or persons in
the Building or caused by operations in construction of any private, public, or
quasi-public work; nor shall Landlord be liable for any latent defect in the
Premises or in the Building; provided however, that: (i) the foregoing shall not
limit Landlord's obligation to repair any latent defect in Landlord's Work of
which Tenant gives Landlord written notice within the time period required
pursuant to Article 4.8, and (ii) the foregoing shall not relieve Landlord of
its obligation to perform maintenance and repairs pursuant to Article 8.7.
Landlord shall cooperate with Tenant in such manner as Tenant shall reasonably
request in the event that Tenant suffers any loss or damage by reason of any
such latent defect so that Tenant shall be able to prosecute any claim which it
may have against the contractor and/or material supplier responsible for such
latent defect. Without limiting the foregoing, Landlord shall assign its right
to Tenant against any such contractor and/or material supplier, if necessary to
enable Tenant to prosecute its claim against any such contractor and/or material
supplier.

         15.6 REPAIRS AND ALTERATIONS--NO DIMINUTION OF RENTAL VALUE. Except as
otherwise provided in Article 18, there shall be no allowance to Tenant for
diminution of rental value and no liability on the part of Landlord by reason of
inconvenience, annoyance or injury to Tenant arising from any repairs,
alterations, additions, replacements or improvements made by Landlord, or any
related work, Tenant or others in or to any portion of the Building or Premises
or any property adjoining the Building, or in or to fixtures, appurtenances, or
equipment thereof, or for failure of Landlord or others to make any repairs,
alterations, additions or improvements in or to any portion of the Building, or
of the Premises, or in or to the fixtures, appurtenances or equipment thereof.

16.      ASSIGNMENT, MORTGAGING AND SUBLETTING

         A. Tenant covenants and agrees that neither this Lease nor the term and
estate hereby granted, nor any interest herein or therein, will be assigned,
mortgaged, pledged, encumbered or otherwise transferred, voluntarily, by
operation of law or otherwise, and that neither the Premises, nor any part
thereof will be encumbered in any manner by reason of any act or omission on the
part of Tenant, or used or occupied, or permitted to be used or occupied, or
utilized for desk space or for mailing privileges, by anyone other than Tenant,
or for any use or purpose other than as stated in Exhibit 1, or be sublet, or
offered or advertised for subletting.

                                      -27-
<PAGE>   37
         B. Notwithstanding anything to the contrary in the Lease contained,
except to the extent set forth in Paragraph C below:

                           1.       Tenant shall, prior to offering or
                                    advertising the Premises, or any portion
                                    thereof for sublease or assignment give
                                    Landlord a Recapture Offer, as hereinafter
                                    defined.

                           2.       For the purposes hereof a "Recapture Offer"
                                    shall be defined as a notice in writing from
                                    Tenant to Landlord which:

                                    (a)      States that Tenant desires to
                                             sublet the Premises, or a portion
                                             thereof, or to assign its interest
                                             in this Lease.

                                    (b)      Identifies the affected portion of
                                             the Premises ("Recapture
                                             Premises").

                                    (c)      Identifies the period of time
                                             ("Recapture Period") during which
                                             Tenant proposes to sublet the
                                             Recapture Premises or to assign its
                                             interest in the Lease.

                                    (d)      Offers to Landlord to terminate the
                                             Lease in respect of the Recapture
                                             Premises (in the case of a proposed
                                             assignment of Tenant's interest in
                                             the Lease or a subletting for the
                                             remainder of the term of the Lease)
                                             or to suspend the term of the Lease
                                             pro tanto in respect of the
                                             Recapture Period (i.e. the term of
                                             the Lease in respect of the
                                             Recapture Premises shall be
                                             terminated during the Recapture
                                             Period and Tenant's rental
                                             obligations shall be reduced in
                                             proportion to the ratio of the
                                             Total Rentable Area of the
                                             Recapture Premises to the Total
                                             Rentable Area of the Premises then
                                             demised to Tenant).

                           3.       Landlord shall have twenty-one (21) business
                                    days to accept a Recapture Offer. If
                                    Landlord does not timely give written notice
                                    to Tenant accepting a Recapture Offer, then
                                    Landlord agrees that, subject to
                                    Subparagraph 5 of this Paragraph B, it will
                                    not unreasonably withhold or delay its
                                    consent to a sublease of the Recapture
                                    Premises for the Recapture Period, or an
                                    assignment of Tenant's interest in the
                                    Lease, as the case may be, to a Qualified
                                    Transferee, as hereinafter defined.

                           4.       For the purposes hereof, a "Qualified
                                    Transferee" shall be defined as a person,
                                    firm or corporation which, in Landlord's
                                    reasonable opinion:

                                    (a)      is financially responsible and of
                                             good reputation (recognizing that
                                             Akamai Technologies, Inc. remains
                                             liable hereunder); and

                                    (b)     is engaged in a business, the
                                            functional aspects of which, with
                                            respect to the Premises, are similar
                                            to the use of other Premises made by
                                            other office space tenants in the
                                            Building.

                           5.       In the event that the proposed assignee or
                                    sublessee is then a tenant or subtenant of
                                    other premises in the Building or the
                                    Complex (an

                                      -28-
<PAGE>   38
                                    "Existing Tenant"), then Tenant's written
                                    request for Landlord's consent to a sublease
                                    or assignment to such entity shall be deemed
                                    to constitute a second Recapture Offer to
                                    Landlord with respect to such proposed
                                    sublease or assignment, except that Landlord
                                    shall have seven (7) calendar days from the
                                    receipt of Tenant's written request for
                                    consent to such proposed sublease or
                                    assignment in which to give Tenant written
                                    notice that Landlord accepts such Recapture
                                    Offer.

                           6.       Notwithstanding anything to the contrary in
                                    this Paragraph B contained:

                                    (a)      If Tenant is in default of its
                                             obligations under the Lease at the
                                             time that it makes the aforesaid
                                             offer to Landlord, such default
                                             shall be deemed to be a
                                             "reasonable" reason for Landlord
                                             withholding its consent to any
                                             proposed subletting or assignment;
                                             and

                                    (b)      If Tenant does not enter into a
                                             sublease with a subtenant (or an
                                             assignment to an assignee, as the
                                             case may be) approved by Landlord,
                                             as aforesaid, on or before the date
                                             which is one hundred eighty (180)
                                             days after the earlier of: (x) the
                                             expiration of said twenty-one (21)
                                             business day period, or (y) the
                                             date that Landlord notifies Tenant
                                             that Landlord will not accept
                                             Tenant's offer to terminate or
                                             suspend the Lease, then Landlord
                                             shall have the right arbitrarily to
                                             withhold its consent to any
                                             subletting or assignment proposed
                                             to be entered into by Tenant after
                                             the expiration of said one hundred
                                             eighty (180) day period unless
                                             Tenant again offers, in accordance
                                             with this Paragraph B, either to
                                             terminate or to suspend the Lease
                                             in respect of the portion of the
                                             Premises proposed to be sublet (or
                                             in respect of the entirety of the
                                             Premises in the event of a proposed
                                             assignment, as the case may be). If
                                             Tenant shall make any subsequent
                                             offers to terminate or suspend the
                                             Lease pursuant to this Paragraph B,
                                             any such subsequent offers shall be
                                             treated in all respects as if it is
                                             Tenant's first offer to suspend or
                                             terminate the Lease pursuant to
                                             this Paragraph B, provided that the
                                             period of time Landlord shall have
                                             in which to accept or reject such
                                             subsequent offer shall be fourteen
                                             (14) business days.

                           7.       Notwithstanding anything to the contrary
                                    herein contained, except in connection with
                                    a Protected Sublease, as defined in
                                    Subparagraph 8 of this Paragraph B, Tenant
                                    shall have no right, under this Paragraph B
                                    hereof, prior to the date that is the
                                    earlier of (i) one (1) year after the Term
                                    Commencement Date in respect of Portion A,
                                    and (ii) the date when Buildings 545, 565
                                    and 575 are one hundred percent (100%)
                                    leased.

                           8.       Notwithstanding the foregoing, Tenant shall
                                    have the right to sublease up to 35,696
                                    square feet of Rentable Floor Area, in the
                                    aggregate, of the Premises for a term not in
                                    excess of forty-two months (a "Protected
                                    Sublease") without the requirement of giving
                                    Landlord a Recapture Notice with respect
                                    thereto, and without being subject to the
                                    provisions

                                      -29-
<PAGE>   39
                                    of Paragraph (7) above. Such Protected
                                    Sublease shall, however, require Landlord's
                                    consent, which shall not be unreasonably
                                    withheld, conditioned or delayed for a
                                    sublease to a Qualified Transferee, as
                                    defined in Paragraph (4) above, and shall be
                                    subject to the provisions of Paragraph (5)
                                    above allowing Landlord to recapture the
                                    relevant portion of the Premises in
                                    connection with subleases or assignments to
                                    Existing Tenants. Tenant shall pay Landlord
                                    50% of the net (i.e., net of the reasonable
                                    and customary brokerage, legal, design and
                                    construction costs incurred by Tenant in
                                    connection with such Protected Sublease)
                                    amount of all rent and other consideration
                                    which Tenant receives as a result of a
                                    Protected Sublease that is in excess of the
                                    rent payable to Landlord for the portion of
                                    the Premises and Term covered by the
                                    Transfer. Tenant shall pay Landlord for
                                    Landlord's share of any excess within ten
                                    (10) days after Tenant's receipt of such
                                    excess consideration.

                           9.       No subletting or assignment shall relieve
                                    Tenant of its primary obligation as
                                    party-Tenant hereunder, nor shall it reduce
                                    or increase Landlord's obligations under the
                                    Lease.

         C. Notwithstanding anything to the contrary herein contained, Tenant
shall have the right, without obtaining Landlord's consent and without giving
Landlord a Recapture Offer, to assign its interest in this Lease and to sublease
the premises, or any portion thereof, to an Affiliated Entity, as hereinafter
defined, so long as such entity remains in such relationship to Tenant, and
provided that prior to or simultaneously with such assignment or sublease, such
Affiliated Entity executes and delivers to Landlord an Assumption Agreement, as
hereinabove defined. For the purposes hereof, an "Affiliated Entity" shall be
defined as any entity which is controlled by, is under common control with, or
which controls Tenant. Notwithstanding anything to the contrary herein
contained, it is hereby expressly understood and agreed, however, that if Tenant
is a corporation, that the assignment or transfer of this Lease, and the term
and estate hereby granted, to any corporation into which Tenant is merged or
with which Tenant is consolidated or which acquires all or substantially all of
its stock or assets which corporation shall have a net worth at least equal to
that of Tenant immediately prior to such merger or consolidation (such
corporation being hereinafter called "Assignee"), shall not be deemed to be
prohibited hereby, or to require Landlord's consent, or to require the
furnishing of a Recapture Offer, if, and upon the express condition that
Assignee and Tenant shall promptly execute, acknowledge and deliver to Landlord
an agreement in form and substance satisfactory to Landlord whereby Assignee
shall agree to be independently bound by and upon all the covenants, agreements,
terms, provisions and conditions set forth in this Lease on the part of Tenant
to be performed, and whereby Assignee shall expressly agree that the provisions
of this Article 16 shall, notwithstanding such assignment or transfer, continue
to be binding upon it with respect to all future assignments and transfers.

         D. If Tenant is an individual who uses and/or occupies the Premises
with partners, or if Tenant is a partnership, then:

                  (i) Each present and future partner shall be personally bound
by and upon all of the covenants, agreements, terms, provisions and conditions
set forth in this Lease on the part of Tenant to be performed; and

                  (ii) In confirmation of the foregoing, Landlord may (but
without being required to do so) request (and Tenant shall duly comply) that
Tenant, at the time that Tenant admits any new partner to its partnership, shall
require each such new partner to execute an agreement in form and substance
satisfactory to Landlord whereby such new partner shall agree to be personally
bound by and upon all of the covenants, agreements, terms, provisions and
conditions of this Lease on the part of Tenant to be

                                      -30-
<PAGE>   40
performed, without regard to the time when such new partner is admitted to
partnership or when any obligations under any such covenants, etc., accrue.

         E. The listing of any name other than that of Tenant, whether on the
doors of the Premises or on the Building directory, or otherwise, shall not
operate to vest in any such other person, firm or corporation any right or
interest in this Lease or in the Premises or be deemed to effect or evidence any
consent of Landlord, it being expressly understood that any such listing is a
privilege extended by Landlord revocable at will by written notice to Tenant.

         F. If this Lease be assigned, or if the Premises or any part thereof be
sublet or occupied by anybody other than Tenant, Landlord may, at any time and
from time to time, collect rent and other charges from the assignee, subtenant
or occupant, and apply the net amount collected to the rent and other charges
herein reserved then due and thereafter becoming due, but no such assignment,
subletting, occupancy or collection shall be deemed a waiver of this covenant,
or the acceptance of the assignee, subtenant or occupant as a tenant, or a
release of Tenant from the further performance by Tenant of covenants on the
part of Tenant herein contained. Any consent by Landlord to a particular
assignment or subletting shall not in any way diminish the prohibition stated in
the first sentence of this Article 16 or the continuing liability of the Tenant
named on Exhibit 1 as the party Tenant under this Lease. No assignment or
subletting shall affect the purpose for which the Premises may be used as stated
in Exhibit 1.

         G. Tenant agrees that in no event shall this Lease be assigned, or all
or any portion of the Premises be sublet, to any of the following entities:
Gardner Group, Inc.; META Group, Inc.; GIGA Information Group, Inc.; Jupiter
Communications; The Yankee Group, a subsidiary of Primark Corporation; Odyssey
Research; and Mainspring Communications, Inc.

17.      MISCELLANEOUS COVENANTS

         Tenant covenants and agrees as follows:

         17.1 RULES AND REGULATIONS. Tenant will faithfully observe and comply
with the Rules and Regulations, if any, annexed hereto and such other and
further reasonable Rules and Regulations as Landlord hereafter at any time or
from time to time may make and may communicate in writing to Tenant, which in
the reasonable judgment of Landlord shall be necessary for the reputation,
safety, care or appearance of the Building, or the preservation of good order
therein, or the operation or maintenance of the Building, or the equipment
thereof, or the comfort of tenants or others in the Building, provided, however,
that in the case of any conflict between the provisions of this Lease and any
such regulations, the provisions of this Lease shall control, and provided
further that nothing contained in this Lease shall be construed to impose upon
Landlord any duty or obligation to enforce the Rules and Regulations or the
terms, covenants or conditions in any other lease as against any other tenant
and Landlord shall not be liable to Tenant for violation of the same by any
other tenant, its servants, employees, agents, contractors, visitors, invitees
or licensees. Notwithstanding anything to the contrary in this Lease contained,
Landlord agrees that it will not enforce said Rules and Regulations against
Tenant in a discriminatory or arbitrary manner.

         17.2 ACCESS TO PREMISES--SHORING. Tenant shall: (i) permit Landlord to
erect, use and maintain pipes, ducts and conduits in and through the Premises,
provided the same do not materially reduce the floor area or materially
adversely affect the appearance thereof; (ii) upon reasonable prior oral notice
(except that no notice shall be required in emergency situations), permit
Landlord and any mortgagee of the Building or the Building and land or of the
interest of Landlord therein, and any lessor under any ground or underlying
lease, and their representatives, to have free and unrestricted access to and to
enter upon the Premises at all reasonable hours for the purposes of inspection
or of making repairs, replacements or improvements in or to the Premises or the
Building or equipment (including, without

                                      -31-
<PAGE>   41
limitation, sanitary, electrical, heating, air conditioning or other systems) or
of complying with all laws, orders and requirements of governmental or other
authority or of exercising any right reserved to Landlord by this Lease
(including the right during the progress of any such repairs, replacements or
improvements or while performing work and furnishing materials in connection
with compliance with any such laws, orders or requirements to take upon or
through, or to keep and store within, the Premises all necessary materials,
tools and equipment); and (iii) permit Landlord, at reasonable times, upon
reasonable advance notice, to show the Premises during ordinary business hours
to any existing or prospective mortgagee, ground lessor, space lessee,
purchaser, or assignee of any mortgage, of the Building or of the Building and
the land or of the interest of Landlord therein, and during the period of 12
months next preceding the Termination Date to any person contemplating the
leasing of the Premises or any part thereof. If, during the last month of the
term, Tenant shall have removed all or substantially all of Tenant's property
therefrom, Landlord may immediately enter and alter, renovate and redecorate the
Premises, without elimination or abatement of rent, or incurring liability to
Tenant for any compensation, and such acts shall have no effect upon this Lease.
If Tenant shall not be personally present to open and permit an entry into the
Premises at any time when for any reason an entry therein shall be necessary or
permissible, Landlord or Landlord's agents may enter the same by a master key,
or may forcibly enter the same, without rendering Landlord or such agents liable
therefor (if during such entry Landlord or Landlord's agents shall accord
reasonable care to Tenant's property), and without in any manner affecting the
obligations and covenants of this Lease. Provided that Landlord shall incur no
additional expense thereby, Landlord shall exercise its rights of access to the
Premises permitted under any of the terms and provisions of this Lease in such
manner as to minimize to the extent practicable interference with Tenant's use
and occupation of the Premises. If an excavation shall be made upon land
adjacent to the Premises or shall be authorized to be made, Tenant shall afford
to the person causing or authorized to cause such excavation, license to enter
upon the Premises for the purpose of doing such work as said person shall deem
necessary to preserve the Building from injury or damage and to support the same
by proper foundations without any claims for damages or indemnity against
Landlord, or diminution or abatement of rent.

         17.3 ACCIDENTS TO SANITARY AND OTHER SYSTEMS. Tenant shall give to
Landlord prompt notice of any fire or accident in the Premises or in the
Building and of any damage to, or defective condition in, any part or
appurtenance of the Building including, without limitation, sanitary,
electrical, ventilation, heating and air conditioning or other systems located
in, or passing through, the Premises. Except as otherwise provided in Articles
18 and 20, and subject to Tenant's obligations in Article 14, such damage or
defective condition shall be remedied by Landlord with reasonable diligence, but
if such damage or defective condition was caused by Tenant or by the employees,
licensees, contractors or invitees of Tenant, the cost to remedy the same shall
be paid by Tenant. In addition, all reasonable costs incurred by Landlord in
connection with the investigation of any notice given by Tenant shall be paid by
Tenant if the reported damage or defective condition was caused by Tenant or by
the employees, licensees, contractors, or invitees of Tenant. Tenant shall not
be entitled to claim any eviction from the Premises or any damages arising from
any such damage or defect unless the same (i) shall have been occasioned by the
negligence of the Landlord, its agents, servants or employees and (ii) shall
not, after notice to Landlord of the condition claimed to constitute negligence,
have been cured or corrected within a reasonable time after such notice has been
received by Landlord; and in case of a claim of eviction unless such damage or
defective condition shall have rendered the Premises untenantable and they shall
not have been made tenantable by Landlord within a reasonable time.

         17.4 SIGNS, BLINDS AND DRAPES. Tenant shall put no signs in any part of
the Building. No signs or blinds may be put on or in any window or elsewhere if
visible from the exterior of the Building, nor may the building standard drapes
or blinds be removed by Tenant. Tenant may hang its own drapes, provided that
they shall not in any way interfere with the building standard drapery or blinds
or be visible from the exterior of the Building and that such drapes are so hung
and installed that when drawn, the building standard drapery or blinds are
automatically also drawn. Any signs or lettering in the public corridors or on
the doors shall conform to Landlord's building standard design. Neither
Landlord's name,

                                      -32-
<PAGE>   42
nor the name of the Building or any Center, Office Park or other Park of which
the Building is a part, or the name of any other structure erected therein shall
be used without Landlord's consent in any advertising material (except on
business stationery or as an address in advertising matter), nor shall any such
name, as aforesaid, be used in any undignified, confusing, detrimental or
misleading manner.

         Provided that and for so long as Akamai Technologies, Inc., itself or
an Assignee or Affiliated Entity (as those terms are defined in Article 16) is
(i) prior to the Term Commencement Date in respect of Portion B, occupying and
paying rent on some part of the Premises, and (ii) after the Term Commencement
Date in respect of Portion B, occupying and paying rent on not less than ninety
percent (90%) of the entirety of Floors 2 through 7 of the Building, Tenant (or
an Assignee or Affiliated Entity occupying the Premises as aforesaid) shall have
the non-exclusive right to erect and maintain not more than two signs on the
exterior of the Building (individually and collectively, the "Exterior Sign") as
described in and subject to the restrictions contained in Exhibit 7 attached
hereto, provided (i) the Exterior Sign complies with all applicable laws and
shall not interfere with the Landlord's signage program for the Building and
Complex (and Tenant shall have obtained any necessary permits prior to erecting
the Exterior Sign), (ii) the Exterior Sign shall be located as described in
Exhibit 7, (iii) the materials, design and lighting of the Exterior Sign, and
any requested changes thereto, shall be subject to Landlord's prior written
approval, which approval shall not be unreasonably withheld, and (iv) Tenant
shall at all times maintain the Exterior Sign in good order and condition and
shall remove the Exterior Signs at the expiration or earlier termination of the
term hereof or upon Landlord's written demand after the failure of condition
(ii) above, and shall repair any damage to the Building caused by the Exterior
Sign or its installation or removal. Landlord agrees, at Tenant's cost, to
reasonably cooperate with Tenant in obtaining any necessary governmental
approvals, permits, etc. in connection with the Exterior Sign.

         17.5 ESTOPPEL CERTIFICATE. Either party shall at any time and from time
to time upon not less than twenty (20) days' prior notice by the other party,
execute, acknowledge and deliver to the requesting party a statement in writing
certifying that this Lease is unmodified and in full force and effect (or if
there have been modifications, that the same is in full force and effect as
modified and stating the modifications), and the dates to which the Yearly Rent
and other charges have been paid in advance, if any, stating whether or not the
other party is in default in performance of any covenant, agreement, term,
provision or condition contained in this Lease and, if so, specifying each such
default and such other facts as the requesting party may reasonably request, it
being intended that any such statement delivered pursuant hereto may be relied
upon by any prospective purchaser of the Building or of the Building and the
land or of any interest of Landlord therein, any mortgagee or prospective
mortgagee thereof, any lessor or prospective lessor thereof, any lessee or
prospective lessee thereof, or any prospective assignee of any mortgage thereof.
Time is of the essence in respect of any such requested certificate, Tenant
hereby acknowledging the importance of such certificates in mortgage financing
arrangements, prospective sale and the like. Tenant hereby appoints Landlord
Tenant's attorney-in-fact in its name and behalf to execute such statement if
Tenant shall fail to execute such statement within such twenty-(20)-day period.

         17.6 PROHIBITED MATERIALS AND PROPERTY. Tenant shall not bring or
permit to be brought or kept in or on the Premises or elsewhere in the Building
(i) any inflammable, combustible or explosive fluid, material, chemical or
substance including, without limitation, any hazardous substances as defined
under Massachusetts General Laws chapter 21E, the Federal Comprehensive
Environmental Response Compensation and Liability Act (CERCLA), 42 USC
Section 9601 et seq., as amended, under Section 3001 of the Federal Resource
Conservation and Recovery Act of 1976, as amended, or under any regulation of
any governmental authority regulating environmental or health matters (except
for standard office supplies stored in proper containers), (ii) any materials,
appliances or equipment (including, without limitation, materials, appliances
and equipment selected by Tenant for the construction or other preparation of
the Premises and furniture and carpeting) which pose any danger to life, safety
or health or may cause damage, injury or death; (iii) any unique, unusually
valuable, rare or exotic property, work of art or the like unless the same is
fully insured under all-risk coverage, or (iv) any data processing, electronic,
optical or other equipment or property of a delicate, fragile or vulnerable
nature unless the same are housed,

                                      -33-
<PAGE>   43
shielded and protected against harm and damage, whether by cleaning or
maintenance personnel, radiations or emanations from other equipment now or
hereafter installed in the Building, or otherwise. Nor shall Tenant cause or
permit any potentially harmful air emissions, odors of cooking or other
processes, or any unusual or other objectionable odors or emissions to emanate
from or permeate the Premises.

         17.7 REQUIREMENTS OF LAW--FINES AND PENALTIES. Tenant at its sole
expense shall comply with all laws, rules, orders and regulations, including,
without limitation, all energy-related requirements, of Federal, State, County
and Municipal Authorities and with any direction of any public officer or
officers, pursuant to law, which shall impose any duty upon Landlord or Tenant
with respect to or arising out of Tenant's use or occupancy of the Premises. In
addition, Tenant shall, at Tenant's sole expense, for so long as the Parking and
Traffic Demand Management Plan dated May 9, 1999 as approved by (and subject to
the conditions set for in such approval) the City of Cambridge on July 9, 1999
remains applicable to the Complex, offer to subsidize mass transit monthly
passes for all of its employees. Tenant shall reimburse and compensate Landlord
for all expenditures made by, or damages or fines sustained or incurred by,
Landlord due to nonperformance or noncompliance with or breach or failure to
observe any item, covenant, or condition of this Lease upon Tenant's part to be
kept, observed, performed or complied with. If Tenant receives notice of any
violation of law, ordinance, order or regulation applicable to the Premises, it
shall give prompt notice thereof to Landlord. Landlord shall comply with any
laws, rules, orders, regulations, energy requirements ("Laws") and with any
direction of any public office or officer relating to the maintenance or
operation of the Building as an office building, and the costs so incurred by
Landlord shall be included in Operating Costs in accordance with the provisions
of Article 9. Landlord hereby represents to Tenant that, as of the Execution
Date of the Lease, Landlord has not received notice from any governmental agency
that the Building or Premises are in violation of any applicable laws.

         17.8 TENANT'S ACTS--EFFECT ON INSURANCE. Tenant shall not do or permit
to be done any act or thing upon the Premises or elsewhere in the Building which
will invalidate or be in conflict with any insurance policies covering the
Building and the fixtures and property therein; and shall not do, or permit to
be done, any act or thing upon the Premises which shall subject Landlord to any
liability or responsibility for injury to any person or persons or to property
by reason of any business or operation being carried on upon said Premises or
for any other reason. Tenant at its own expense shall comply with all rules,
orders, regulations and requirements of the Board of Fire Underwriters, or any
other similar body having jurisdiction, and shall not (i) do, or permit anything
to be done, in or upon the Premises, or bring or keep anything therein, except
as now or hereafter permitted by the Fire Department, Board of Underwriters,
Fire Insurance Rating Organization, or other authority having jurisdiction, and
then only in such quantity and manner of storage as will not increase the rate
for any insurance applicable to the Building, or (ii) use the Premises in a
manner which shall increase such insurance rates on the Building, or on property
located therein, over that applicable when Tenant first took occupancy of the
Premises hereunder. If by reason of the failure of Tenant to comply with the
provisions hereof the insurance rate applicable to any policy of insurance shall
at any time thereafter be higher than it otherwise would be, the Tenant shall
reimburse Landlord for that part of any insurance premiums thereafter paid by
Landlord, which shall have been charged because of such failure by Tenant.

         17.9 MISCELLANEOUS. Tenant shall not suffer or permit the Premises or
any fixtures, equipment or utilities therein or serving the same, to be
overloaded, damaged or defaced, nor permit any hole to be drilled or made in any
part thereof. Tenant shall not suffer or permit any employee, contractor,
business invitee or visitor to violate any covenant, agreement or obligations of
the Tenant under this Lease.

18.      DAMAGE BY FIRE, ETC.

         During the entire term of this Lease, and adjusting insurance coverages
to reflect current values from time to time:--(i) Landlord shall keep the
Building (excluding work, installations, improvements and

                                      -34-
<PAGE>   44
betterments made in either Portion of the Premises after the Term Commencement
Date in respect of such Portion of the Premises [called "Over-Building-Standard
Property"] and any other property installed by or at the expense of Tenant)
insured against loss or damage caused by any peril covered under fire, extended
coverage and all risk insurance in an amount equal to one hundred percent (100%)
replacement cost value above foundation walls; and (ii) Tenant shall keep its
personal property in and about the Premises and the Over-Building-Standard
Property insured against loss or damage caused by any peril covered under fire,
extended coverage and all risk insurance in an amount equal to one hundred
percent (100%) replacement cost value. Such Tenant's insurance shall insure the
interests of both Landlord and Tenant as their respective interests may appear
from time to time and shall name Landlord as an additional insured; and the
proceeds thereof shall be used only for the replacement or restoration of such
personal property and the Over-Building-Standard Property.

         If any portion of the Premises required to be insured by Landlord under
the preceding paragraph shall be damaged by fire or other insured casualty,
Landlord shall proceed with diligence, subject to the then applicable statutes,
building codes, zoning ordinances, and regulations of any governmental
authority, and at the expense of Landlord (but only to the extent of insurance
proceeds made available to Landlord by any mortgagee and/or ground lessor of the
real property of which the Premises are a part) to repair or cause to be
repaired such damage, provided, however, in respect of any over-Building
Standard Property as shall have been damaged by such fire or other casualty and
which (in the judgment of Landlord) can more effectively be repaired as an
integral part of Landlord's repair work on the Premises, that such repairs to
such Tenant's alterations, decorations, additions and improvements shall be
performed by Landlord but at Tenant's expense; in all other respects, all
repairs to and replacements of Tenant's property and Over-Building-Standard
Property shall be made by and at the expense of Tenant. If the Premises or any
part thereof shall have been rendered unfit for use and occupation hereunder by
reason of such damage the Yearly Rent or a just and proportionate part thereof,
according to the nature and extent to which the Premises shall have been so
rendered unfit, shall be suspended or abated until the Premises (except as to
the property which is to be repaired by or at the expense of Tenant) shall have
been restored as nearly as practicably may be to the condition in which they
were immediately prior to such fire or other casualty. Tenant agrees to
cooperate with Landlord in such manner as Landlord may reasonably request in
assisting Landlord in collecting insurance proceeds due in connection with any
casualty which affects the Premises. Landlord shall not be liable for delays in
the making of any such repairs which are due to government regulation,
casualties and strikes, unavailability of labor and materials, and other causes
beyond the reasonable control of Landlord, nor shall Landlord be liable for any
inconvenience or annoyance to Tenant or injury to the business of Tenant
resulting from delays in repairing such damage.

         Landlord's Termination Rights. If (i) the Premises are so damaged by
fire or other casualty (whether or not insured) at any time during the last
thirty months of the term hereof that the cost to repair such damage is
reasonably estimated to exceed one third of the total Yearly Rent payable
hereunder for the period from the estimated date of restoration until the
Termination Date, or (ii) the Building (whether or not including any portion of
the Premises) is so damaged by fire or other casualty (whether or not insured)
that substantial alteration or reconstruction or demolition of the Building
shall in Landlord's judgment be required, then and in either of such events,
this Lease and the term hereof may be terminated at the election of Landlord by
a notice in writing of its election so to terminate which shall be given by
Landlord to Tenant within sixty (60) days following such fire or other casualty,
the effective termination date of which shall be not less than thirty (30) days
after the day on which such termination notice is received by Tenant. In the
event of any termination, this Lease and the term hereof shall expire as of such
effective termination date as though that were the Termination Date as stated in
Exhibit 1 and the Yearly Rent shall be apportioned as of such date; and if the
Premises or any part thereof shall have been rendered unfit for use and
occupation by reason of such damage the Yearly Rent for the period from the date
of the fire or other casualty to the effective termination date, or a just and
proportionate part thereof, according to the nature and extent to which the
Premises shall have been so rendered unfit, shall be abated.

                                      -35-
<PAGE>   45
         Tenant's Termination Rights. In the event that the premises or the
Building are damaged by fire or other casualty to such an extent so as to render
the premises untenantable, and if Landlord shall fail to substantially complete
said repairs or restoration within two hundred fifty (250) days (sixty (60) days
in the case of a fire or other casualty occurring during the last twelve (12)
months of the term hereof, as the same may have been extended) after the date of
such fire or other casualty for any reason other than Tenant's fault, Tenant may
terminate this Lease by giving Landlord written notice as follows:

         (a)      Said notice shall be given after said two hundred fifty (250)
                  day period or sixty (60) day period, as the case may be.

         (b)      Said notice shall set forth an effective date which is not
                  earlier than thirty (30) days after Landlord receives said
                  notice.

         (c)      If said repairs or restoration are substantially complete on
                  or before the date thirty (30) days (which thirty-(30)-day
                  period shall be extended by the length of any delays caused by
                  Tenant or Tenant's contractors) after Landlord receives such
                  notice, said notice shall have no further force and effect.

         (d)      If said repairs or restoration are not substantially complete
                  on or before the date thirty (30) days (which thirty-(30)-day
                  period shall be extended by the length of any delays caused by
                  Tenant or Tenant's contractors) after Landlord receives such
                  notice, the Lease shall terminate as of said effective date.

19.      WAIVER OF SUBROGATION

         In any case in which Tenant shall be obligated to pay to Landlord any
loss, cost, damage, liability, or expense suffered or incurred by Landlord,
Landlord shall allow to Tenant as an offset against the amount thereof (i) the
net proceeds of any insurance collected by Landlord for or on account of such
loss, cost, damage, liability or expense, provided that the allowance of such
offset does not invalidate or prejudice the policy or policies under which such
proceeds were payable, and (ii) if such loss, cost, damage, liability or expense
shall have been caused by a peril against which Landlord has agreed to procure
insurance coverage under the terms of this Lease, the amount of such insurance
coverage, whether or not actually procured by Landlord.

         In any case in which Landlord or Landlord's managing agent shall be
obligated to pay to Tenant any loss, cost, damage, liability or expense suffered
or incurred by Tenant, Tenant shall allow to Landlord or Landlord's managing
agent, as the case may be, as an offset against the amount thereof (i) the net
proceeds of any insurance collected by Tenant for or on account of such loss,
cost, damage, liability, or expense, provided that the allowance of such offset
does not invalidate the policy or policies under which such proceeds were
payable and (ii) the amount of any loss, cost, damage, liability or expense
caused by a peril covered by fire insurance with the broadest form of property
insurance generally available on property in buildings of the type of the
Building, whether or not actually procured by Tenant.

         The parties hereto shall each procure an appropriate clause in, or
endorsement on, any property insurance policy covering the Premises and the
Building and personal property, fixtures and equipment located thereon and
therein, pursuant to which the insurance companies waive subrogation or consent
to a waiver of right of recovery in favor of either party, its respective agents
or employees. Having obtained such clauses and/or endorsements, each party
hereby agrees that it will not make any claim against or seek to recover from
the other or its agents or employees for any loss or damage to its property or
the property of others resulting from fire or other perils covered by such
property insurance.

                                      -36-
<PAGE>   46

20.      CONDEMNATION - EMINENT DOMAIN

         In the event that the Premises or any part thereof, or the whole or any
part of the Building, shall be taken or appropriated by eminent domain or shall
be condemned for any public or quasi-public use, or (by virtue of any such
taking, appropriation or condemnation) shall suffer any damage (direct, indirect
or consequential) for which Landlord or Tenant shall be entitled to
compensation, then (and in any such event) this Lease and the term hereof may be
terminated at the election of Landlord by a notice in writing of its election so
to terminate which shall be given by Landlord to Tenant within sixty (60) days
following the date on which Landlord shall have received notice of such taking,
appropriation or condemnation. In the event that a substantial part of the
Premises or of the means of access thereto shall be so taken, appropriated or
condemned, then (and in any such event) this Lease and the term hereof may be
terminated at the election of Tenant by a notice in writing of its election so
to terminate which shall be given by Tenant to Landlord within sixty (60) days
following the date on which Tenant shall have received notice of such taking,
appropriation or condemnation.

         Upon the giving of any such notice of termination (either by Landlord
or Tenant) this Lease and the term hereof shall terminate on or retroactively as
of the date on which Tenant shall be required to vacate any part of the Premises
or shall be deprived of a substantial part of the means of access thereto,
provided, however, that Landlord may in Landlord's notice elect to terminate
this Lease and the term hereof retroactively as of the date on which such
taking, appropriation or condemnation became legally effective. In the event of
any such termination, this Lease and the term hereof shall expire as of such
effective termination date as though that were the Termination Date as stated in
Exhibit 1, and the Yearly Rent shall be apportioned as of such date. If neither
party (having the right so to do) elects to terminate Landlord will, with
reasonable diligence and at Landlord's expense, restore the remainder of the
Premises, or the remainder of the means of access, as nearly as practicably may
be to the same condition as obtained prior to such taking, appropriation or
condemnation in which event (i) the Total Rentable Area shall be adjusted as in
Exhibit 5 provided, (ii) a just proportion of the Yearly Rent, according to the
nature and extent of the taking, appropriation or condemnation and the resulting
permanent injury to the Premises and the means of access thereto, shall be
permanently abated, and (iii) a just proportion of the remainder of the Yearly
Rent, according to the nature and extent of the taking, appropriation or
condemnation and the resultant injury sustained by the Premises and the means of
access thereto, shall be abated until what remains of the Premises and the means
of access thereto shall have been restored as fully as may be for permanent use
and occupation by Tenant hereunder. Except for any award specifically
reimbursing Tenant for moving or relocation expenses, there are expressly
reserved to Landlord all rights to compensation and damages created, accrued or
accruing by reason of any such taking, appropriation or condemnation, in
implementation and in confirmation of which Tenant does hereby acknowledge that
Landlord shall be entitled to receive all such compensation and damages, grant
to Landlord all and whatever rights (if any) Tenant may have to such
compensation and damages, and agree to execute and deliver all and whatever
further instruments of assignment as Landlord may from time to time request. In
the event of any taking of the Premises or any part thereof for temporary (i.e.,
not in excess of one (1) year) use, (i) this Lease shall be and remain
unaffected thereby, and (ii) Tenant shall be entitled to receive for itself any
award made to the extent allocable to the Premises in respect of such taking on
account of such use, provided, that if any taking is for a period extending
beyond the term of this Lease, such award shall be apportioned between Landlord
and Tenant as of the Termination Date or earlier termination of this Lease.

21.      DEFAULT

         21.1 CONDITIONS OF LIMITATION - RE-ENTRY - TERMINATION. This Lease and
the herein term and estate are, upon the condition that if (a) subject to
Article 21.7, Tenant shall neglect or fail to perform or observe any of the
Tenant's covenants or agreements herein, including (without limitation) the
covenants or agreements with regard to the payment when due of rent, additional
charges, reimbursement for increase in Landlord's costs, or any other charge
payable by Tenant to Landlord (all of which shall be

                                      -37-
<PAGE>   47
considered as part of Yearly Rent for the purposes of invoking Landlord's
statutory or other rights and remedies in respect of payment defaults); or (b)
Tenant shall desert or abandon the Premises or the same shall become vacant
(whether or not the keys shall have been surrendered or the rent shall have been
paid); or (c) Tenant shall be involved in financial difficulties as evidenced by
an admission in writing by Tenant of Tenant's inability to pay its debts
generally as they become due, or by the making or offering to make a composition
of its debts with its creditors; or (d) Tenant shall make an assignment or trust
mortgage, or other conveyance or transfer of like nature, of all or a
substantial part of its property for the benefit of its creditors, or (e) an
attachment on mesne process, on execution or otherwise, or other legal process
shall issue against Tenant or its property and a sale of any of its assets shall
be held thereunder; or (f) any judgment, final beyond appeal or any lien,
attachment or the like in excess of [$250,000.00] shall be entered, recorded or
filed against Tenant in any court, registry, etc. and Tenant shall fail to pay
such judgment within thirty (30) days after the judgment shall have become final
beyond appeal or to discharge or secure by surety bond such lien, attachment,
etc. within thirty (30) days of such entry, recording or filing, as the case may
be; or (g) the leasehold hereby created shall be taken on execution or by other
process of law and shall not be revested in Tenant within thirty (30) days
thereafter; or (h) a receiver, sequesterer, trustee or similar officer shall be
appointed by a court of competent jurisdiction to take charge of all or any part
of Tenant's property and such appointment shall not be vacated within thirty
(30) days; or (i) any proceeding shall be instituted by or against Tenant
pursuant to any of the provisions of any Act of Congress or State law relating
to bankruptcy, reorganizations, arrangements, compositions or other relief from
creditors, and, in the case of any proceeding instituted against it, if Tenant
shall fail to have such proceedings dismissed within thirty (30) days or if
Tenant is adjudged bankrupt or insolvent as a result of any such proceeding, or
(j) any event shall occur or any contingency shall arise whereby this Lease, or
the term and estate thereby created, would (by operation of law or otherwise)
devolve upon or pass to any person, firm or corporation other than Tenant,
except as expressly permitted under Article 16 hereof - then, and in any such
event (except as hereinafter in Article 21.2 otherwise provided) Landlord may,
by notice to Tenant, elect to terminate this Lease; and thereupon (and without
prejudice to any remedies which might otherwise be available for arrears of rent
or other charges due hereunder or preceding breach of covenant or agreement and
without prejudice to Tenant's liability for damages as hereinafter stated), upon
the giving of such notice, this Lease shall terminate as of the date specified
therein as though that were the Termination Date as stated in Exhibit 1. Without
being taken or deemed to be guilty of any manner of trespass or conversion, and
without being liable to indictment, prosecution or damages therefor, Landlord
may, forcibly if necessary, enter into and upon the Premises (or any part
thereof in the name of the whole); repossess the same as of its former estate;
and expel Tenant and those claiming under Tenant. Wherever "Tenant " is used in
subdivisions (c), (d), (e), (f), (g), (h) and (i) of this Article 21.1, it shall
be deemed to include any one of (i) any corporation of which Tenant is a
controlled subsidiary and (ii) any guarantor of any of Tenant's obligations
under this Lease. The words "re-entry" and "re-enter" as used in this Lease are
not restricted to their technical legal meanings.

         21.2     INTENTIONALLY OMITTED.

         21.3 DAMAGES - TERMINATION. Upon the termination of this Lease under
the provisions of this Article 21, then except as hereinabove in Article 21.2
otherwise provided, Tenant shall pay to Landlord the rent and other charges
payable by Tenant to Landlord up to the time of such termination, shall continue
to be liable for any preceding breach of covenant, and in addition, shall pay to
Landlord as damages, at the election of Landlord

         either:

                  (x) the amount by which, at the time of the termination of
this Lease (or at any time thereafter if Landlord shall have initially elected
damages under subparagraph (y), below), (i) the aggregate of the rent and other
charges projected over the period commencing with such termination and ending on
the Termination Date as stated in Exhibit 1 exceeds (ii) the aggregate projected
rental value of the Premises for such period;

                                      -38-
<PAGE>   48
         or:

                  (y) amounts equal to the rent and other charges which would
have been payable by Tenant had this Lease not been so terminated, payable upon
the due dates therefor specified herein following such termination and until the
Termination Date as specified in Exhibit 1, provided, however, if Landlord shall
re-let the Premises during such period, that Landlord shall credit Tenant with
the net rents received by Landlord from such re-letting, such net rents to be
determined by first deducting from the gross rents as and when received by
Landlord from such re-letting the expenses incurred or paid by Landlord in
terminating this Lease, as well as the expenses of re-letting, including
altering and preparing the Premises for new tenants, brokers' commissions, and
all other similar and dissimilar expenses properly chargeable against the
Premises and the rental therefrom, it being understood that any such re-letting
may be for a period equal to or shorter or longer than the remaining term of
this Lease; and provided, further, that (i) in no event shall Tenant be entitled
to receive any excess of such net rents over the sums payable by Tenant to
Landlord hereunder and (ii) in no event shall Tenant be entitled in any suit for
the collection of damages pursuant to this Subparagraph (y) to a credit in
respect of any net rents from a re-letting except to the extent that such net
rents are actually received by Landlord prior to the commencement of such suit.
If the Premises or any part thereof should be re-let in combination with other
space, then proper apportionment on a square foot area basis shall be made of
the rent received from such re-letting and of the expenses of re-letting.

         In calculating the rent and other charges under Subparagraph (x),
above, there shall be included, in addition to the Yearly Rent, Tax Excess and
Operating Expense Excess and all other considerations agreed to be paid or
performed by Tenant, on the assumption that all such amounts and considerations
would have remained constant (except as herein otherwise provided) for the
balance of the full term hereby granted.

         Suit or suits for the recovery of such damages, or any installments
thereof, may be brought by Landlord from time to time at its election, and
nothing contained herein shall be deemed to require Landlord to postpone suit
until the date when the term of this Lease would have expired if it had not been
terminated hereunder.

         Nothing herein contained shall be construed as limiting or precluding
the recovery by Landlord against Tenant of any sums or damages to which, in
addition to the damages particularly provided above, Landlord may lawfully be
entitled by reason of any default hereunder on the part of Tenant.

         21.4     FEES AND EXPENSES.

                  (a) If Tenant shall default in the performance of any covenant
on Tenant's part to be performed as in this Lease contained, Landlord may, upon
reasonable advance notice, except that no notice shall be required in an
emergency, immediately, or at any time thereafter, without notice, perform the
same for the account of Tenant. If Landlord at any time is compelled to pay or
elects to pay any sum of money, or do any act which will require the payment of
any sum of money, by reason of the failure of Tenant to comply with any
provision hereof, or if Landlord is compelled to or does incur any expense,
including reasonable attorneys' fees, in instituting, prosecuting, and/or
defending any action or proceeding instituted by reason of any default of Tenant
hereunder, Tenant shall on demand pay to Landlord by way of reimbursement the
sum or sums so paid by Landlord with all costs and damages, plus interest
computed as provided in Article 6 hereof.

                  (b) Tenant shall pay Landlord's cost and expense, including
reasonable attorneys' fees, incurred (i) in enforcing any obligation of Tenant
under this Lease or (ii) as a result of Landlord, without its fault, being made
party to any litigation pending by or against Tenant or any persons claiming
through or under Tenant. Tenant shall not be obligated to make any payment to
Landlord of any

                                      -39-
<PAGE>   49
attorneys' fees incurred by Landlord unless judgment is entered (final, and
beyond appeal) in favor of Landlord in the lawsuit relating to such fees.
Landlord shall pay, upon demand by Tenant, reasonable attorneys' fees incurred
by Tenant in connection with any lawsuit between Landlord and Tenant where
judgment is entered (final, and beyond appeal) in favor of Tenant.

         21.5 WAIVER OF REDEMPTION. Tenant does hereby waive and surrender all
rights and privileges which it might have under or by reason of any present or
future law to redeem the Premises or to have a continuance of this Lease for the
term hereby demised after being dispossessed or ejected therefrom by process of
law or under the terms of this Lease or after the termination of this Lease as
herein provided.

         21.6 LANDLORD'S REMEDIES NOT EXCLUSIVE. The specified remedies to which
Landlord may resort hereunder are cumulative and are not intended to be
exclusive of any remedies or means of redress to which Landlord may at any time
be lawfully entitled, and Landlord may invoke any remedy (including the remedy
of specific performance) allowed at law or in equity as if specific remedies
were not herein provided for.

         21.7 GRACE PERIOD. Notwithstanding anything to the contrary in this
Article contained, Landlord agrees not to take any action to terminate this
Lease (a) for default by Tenant in the payment when due of any sum of money, if
Tenant shall cure such default within five (5) business days after written
notice thereof is given by Landlord to Tenant, or (b) for default by Tenant in
the performance of any covenant other than a covenant to pay a sum of money, if
Tenant shall cure such default within a period of thirty (30) days after written
notice thereof given by Landlord to Tenant (except where the nature of the
default is such that remedial action should appropriately take place sooner, as
indicated in such written notice), or within such additional period as may
reasonably be required to cure such default if (because of governmental
restrictions or any other cause beyond the reasonable control of Tenant) the
default is of such a nature that it cannot reasonably be cured within such
thirty-(30)-day period, provided, however, (1) that there shall be no extension
of time beyond such thirty-(30)-day period for the curing of any such default
unless, not more than ten (10) days after the receipt of the notice of default,
Tenant in writing (i) shall specify the cause on account of which the default
cannot be cured during such period and shall advise Landlord of its intention
duly to institute all steps necessary to cure the default and (ii) shall, as
soon as reasonably practicable, duly institute and thereafter diligently
prosecute to completion all steps necessary to cure such default and, (2) that
no notice of the opportunity to cure a default need be given, and no grace
period whatsoever shall be allowed to Tenant, if the default is incurable or if
the covenant or condition the breach of which gave rise to default had, by
reason of a breach on two (2) prior occasions within the immediately preceding
twelve (12) month period, been the subject of a notice hereunder to cure such
default.

         Notwithstanding anything to the contrary in this Article 21.7
contained, except to the extent prohibited by applicable law, any statutory
notice and grace periods provided to Tenant by law are hereby expressly waived
by Tenant.

22.      END OF TERM - ABANDONED PROPERTY

         Upon the expiration or other termination of the term of this Lease,
Tenant shall peaceably quit and surrender to Landlord the Premises and all
alterations and additions thereto, broom clean, in good order, repair and
condition (except as provided herein and in Articles 8.7, 18 and 20) excepting
only ordinary wear and use and damage by fire or other casualty for which, under
other provisions of this Lease, Tenant has no responsibility of repair or
restoration. Tenant shall remove all of its property and, to the extent
specified by Landlord, all alterations and additions made by Tenant and all
partitions wholly within the Premises, and shall repair any damages to the
Premises or the Building caused by their installation or by such removal.
Tenant's obligation to observe or perform this covenant shall survive the
expiration or other termination of the term of this Lease.

                                      -40-
<PAGE>   50
         Tenant will remove any personal property from the Building and the
Premises upon or prior to the expiration or termination of this Lease and any
such property which shall remain in the Building or the Premises thereafter
shall be conclusively deemed to have been abandoned, and may either be retained
by Landlord as its property or sold or otherwise disposed of in such manner as
Landlord may see fit. If any part thereof shall be sold, that Landlord may
receive and retain the proceeds of such sale and apply the same, at its option,
against the expenses of the sale, the cost of moving and storage, any arrears of
Yearly Rent, additional or other charges payable hereunder by Tenant to Landlord
and any damages to which Landlord may be entitled under Article 21 hereof or
pursuant to law.

         If Tenant or anyone claiming under Tenant shall remain in possession of
the Premises or any part thereof after the expiration or prior termination of
the term of this Lease without any agreement in writing between Landlord and
Tenant with respect thereto, then, prior to the acceptance of any payments for
rent or use and occupancy by Landlord, the person remaining in possession shall
be deemed a tenant-at-sufferance. Whereas the parties hereby acknowledge that
Landlord may need the Premises after the expiration or prior termination of the
term of the Lease for other tenants and that the damages which Landlord may
suffer as the result of Tenant's holding-over cannot be determined as of the
Execution Date hereof, in the event that Tenant so holds over, Tenant shall pay
to Landlord in addition to all rental and other charges due and accrued under
the Lease prior to the date of termination, charges (based upon fair market
rental value of the Premises) for use and occupation of the Premises thereafter
and, in addition to such sums and any and all other rights and remedies which
Landlord may have at law or in equity, an additional use and occupancy charge in
the amount of fifty percent (50%) of either the Yearly Rent and other charges
calculated (on a daily basis) at the highest rate payable under the terms of
this Lease, but measured from the day on which Tenant's hold-over commenced and
terminating on the day on which Tenant vacates the Premises or the fair market
value of the Premises for such period, whichever is greater. In addition, Tenant
shall save Landlord, its agents and employees, harmless and will exonerate,
defend and indemnify Landlord, its agents and employees, from and against any
and all damages which Landlord may suffer on account of Tenant's hold-over in
the Premises after the expiration or prior termination of the term of the Lease.
Notwithstanding the foregoing, Tenant shall not be liable for consequential
damages incurred by Landlord based upon any holdover by Tenant after the
expiration or prior termination of the term of the Lease unless such holdover
continues for sixty (60) or more days after the termination of this Lease or
Tenant's right to possession.

23.      SUBORDINATION

         (a) Subject to any mortgagee's or ground lessor's election, as
hereinafter provided for, this Lease is subject and subordinate in all respects
to all matters of record (including, without limitation, deeds and land
disposition agreements), ground leases and/or underlying leases, and all
mortgages, any of which may now or hereafter be placed on or affect such leases
and/or the real property of which the Premises are a part, or any part of such
real property, and/or Landlord's interest or estate therein, and to each advance
made and/or hereafter to be made under any such mortgages, and to all renewals,
modifications, consolidations, replacements and extensions thereof and all
substitutions therefor. This Article 23 shall be self-operative and no further
instrument or subordination shall be required. In confirmation of such
subordination, Tenant shall execute, acknowledge and deliver promptly any
certificate or instrument that Landlord and/or any mortgagee and/or lessor under
any ground or underlying lease and/or their respective successors in interest
may request, subject to Landlord's, mortgagee's and ground lessor's right to do
so for, on behalf and in the name of Tenant under certain circumstances, as
hereinafter provided. Tenant acknowledges that, where applicable, any consent or
approval hereafter given by Landlord may be subject to the further consent or
approval of such mortgagee and/or ground lessor; and the failure or refusal of
such mortgagee and/or ground lessor to give such consent or approval shall,
notwithstanding anything to the contrary in this Lease contained, constitute
reasonable justification for Landlord's withholding its consent or approval.
Landlord hereby represents to Tenant that, as of the Execution Date of this
Lease, there is no mortgage affecting the Premises or the

                                      -41-
<PAGE>   51
Building. Notwithstanding anything to the contrary in this Article 23 contained,
as to any future mortgages, ground leases, and/or underlying lease or deeds of
trust, the herein provided subordination and attornment shall be effective only
if the mortgagee, ground lessor or trustee therein, as the case may be, agrees,
by a written instrument in recordable form and in the customary form of such
mortgagee, ground lessor, or trustee ("Nondisturbance Agreement") that, as long
as Tenant shall not be in terminable default of the obligations on its part to
be kept and performed under the terms of this Lease, this Lease will not be
affected and Tenant's possession hereunder will not be disturbed by any default
in, termination, and/or foreclosure of, such mortgage, ground lease, and/or
underlying lease or deed of trust, as the case may be.

         (b) Any such mortgagee or ground lessor may from time to time
subordinate or revoke any such subordination of the mortgage or ground lease
held by it to this Lease. Such subordination or revocation, as the case may be,
shall be effected by written notice to Tenant and by recording an instrument of
subordination or of such revocation, as the case may be, with the appropriate
registry of deeds or land records and to be effective without any further act or
deed on the part of Tenant. In confirmation of such subordination or of such
revocation, as the case may be, Tenant shall execute, acknowledge and promptly
deliver any certificate or instrument that Landlord, any mortgagee or ground
lessor may request, subject to Landlord's, mortgagee's and ground lessor's right
to do so for, on behalf and in the name of Tenant under certain circumstances,
as hereinafter provided.

         (c) Without limitation of any of the provisions of this Lease, if any
ground lessor or mortgagee shall succeed to the interest of Landlord by reason
of the exercise of its rights under such ground lease or mortgage (or the
acceptance of voluntary conveyance in lieu thereof) or any third party
(including, without limitation, any foreclosure purchaser or mortgage receiver)
shall succeed to such interest by reason of any such exercise or the expiration
or sooner termination of such ground lease, however caused, then such successor
may, upon notice and request to Tenant (which, in the case of a ground lease,
shall be within thirty (30) days after such expiration or sooner termination),
succeed to the interest of Landlord under this Lease, provided, however, that
such successor shall not: (i) be liable for any previous act or omission of
Landlord under this Lease; (ii) be subject to any offset, defense, or
counterclaim which shall theretofore have accrued to Tenant against Landlord;
(iii) have any obligation with respect to any security deposit unless it shall
have been paid over or physically delivered to such successor; or (iv) be bound
by any previous modification of this Lease or by any previous payment of Yearly
Rent for a period greater than one (1) month, made without such ground lessor's
or mortgagee's consent where such consent is required by applicable ground lease
or mortgage documents. In the event of such succession to the interest of the
Landlord -- and notwithstanding that any such mortgage or ground lease may
antedate this Lease -- the Tenant shall attorn to such successor and shall ipso
facto be and become bound directly to such successor in interest to Landlord to
perform and observe all the Tenant's obligations under this Lease without the
necessity of the execution of any further instrument. Nevertheless, Tenant
agrees at any time and from time to time during the term hereof to execute a
suitable instrument in confirmation of Tenant's agreement to attorn, as
aforesaid, subject to Landlord's, mortgagee's and ground lessor's right to do so
for, on behalf and in the name of Tenant under certain circumstances, as
hereinafter provided.

         (d) The term "mortgage(s)" as used in this Lease shall include any
mortgage or deed of trust. The term "mortgagee(s)" as used in this Lease shall
include any mortgagee or any trustee and beneficiary under a deed of trust or
receiver appointed under a mortgage or deed of trust. The term "mortgagor(s)" as
used in this Lease shall include any mortgagor or any grantor under a deed of
trust.

         (e) Tenant hereby irrevocably constitutes and appoints Landlord or any
such mortgagee or ground lessor, and their respective successors in interest,
acting singly, Tenant's attorney-in-fact to execute and deliver any such
certificate or instrument for, on behalf and in the name of Tenant, but only if
Tenant fails to execute, acknowledge and deliver any such certificate or
instrument within twenty (20) days after Landlord or such mortgagee or such
ground lessor has made written request therefor.

                                      -42-
<PAGE>   52
         (f) Notwithstanding anything to the contrary contained in this Article
23, if all or part of Landlord's estate and interest in the real property of
which the Premises are a part shall be a leasehold estate held under a ground
lease, then: (i) the foregoing subordination provisions of this Article 23 shall
not apply to any mortgages of the fee interest in said real property to which
Landlord's leasehold estate is not otherwise subject and subordinate; and (ii)
the provisions of this Article 23 shall in no way waive, abrogate or otherwise
affect any agreement by any ground lessor (x) not to terminate this Lease
incident to any termination of such ground lease prior to its term expiring or
(y) not to name or join Tenant in any action or proceeding by such ground lessor
to recover possession of such real property or for any other relief. As of the
Execution Date of this Lease, there is no ground lease of the Building or the
real property of which the Building is a part.

         (g) In the event of any failure by Landlord to perform, fulfill or
observe any agreement by Landlord herein, in no event will the Landlord be
deemed to be in default under this Lease permitting Tenant to exercise any or
all rights or remedies under this Lease until the Tenant shall have given
written notice of such failure to any mortgagee (ground lessor and/or trustee)
of which Tenant shall have been advised and until a reasonable period of time
shall have elapsed following the giving of such notice, during which such
mortgagee (ground lessor and/or trustee) shall have the right, but shall not be
obligated, to remedy such failure.

24.      QUIET ENJOYMENT

         Landlord covenants that if, and so long as, Tenant keeps and performs
each and every covenant, agreement, term, provision and condition herein
contained on the part and on behalf of Tenant to be kept and performed, Tenant
shall quietly enjoy the Premises from and against the claims of all persons
claiming by, through or under Landlord subject, nevertheless, to the covenants,
agreements, terms, provisions and conditions of this Lease and to the mortgages,
ground leases and/or underlying leases to which this Lease is subject and
subordinate, as hereinabove set forth.

         Without incurring any liability to Tenant, Landlord may permit access
to the Premises and open the same, whether or not Tenant shall be present, upon
any demand of any receiver, trustee, assignee for the benefit of creditors,
sheriff, marshal or court officer entitled to, or reasonably purporting to be
entitled to, such access for the purpose of taking possession of, or removing,
Tenant's property or for any other lawful purpose (but this provision and any
action by Landlord hereunder shall not be deemed a recognition by Landlord that
the person or official making such demand has any right or interest in or to
this Lease, or in or to the Premises), or upon demand of any representative of
the fire, police, building, sanitation or other department of the city, state or
federal governments.

25.      ENTIRE AGREEMENT -- WAIVER -- SURRENDER

         25.1 ENTIRE AGREEMENT. This Lease and the Exhibits made a part hereof
contain the entire and only agreement between the parties and any and all
statements and representations, written and oral, including previous
correspondence and agreements between the parties hereto, are merged herein.
Tenant acknowledges that all representations and statements upon which it relied
in executing this Lease are contained herein and that the Tenant in no way
relied upon any other statements or representations, written or oral. Any
executory agreement hereafter made shall be ineffective to change, modify,
discharge or effect an abandonment of this Lease in whole or in part unless such
executory agreement is in writing and signed by the party against whom
enforcement of the change, modification, discharge or abandonment is sought.

         25.2 WAIVER. The failure of either party to seek redress for violation,
or to insist upon the strict performance, of any covenant or condition of this
Lease, or any of the Rules and Regulations promulgated hereunder, shall not
prevent a subsequent act, which would have originally constituted a violation,
from having all the force and effect of an original violation. The receipt by
Landlord of rent

                                      -43-
<PAGE>   53
with knowledge of the breach of any covenant of this Lease shall not be deemed a
waiver of such breach. The failure of Landlord to enforce any of such Rules and
Regulations against Tenant and/or any other tenant in the Building shall not be
deemed a waiver of any such Rules and Regulations. No provisions of this Lease
shall be deemed to have been waived by either party unless such waiver be in
writing signed by such party. No payment by Tenant or receipt by Landlord of a
lesser amount than the monthly rent herein stipulated shall be deemed to be
other than on account of the stipulated rent, nor shall any endorsement or
statement on any check or any letter accompanying any check or payment as rent
be deemed an accord and satisfaction, and Landlord may accept such check or
payment without prejudice to Landlord's right to recover the balance of such
rent or pursue any other remedy in this Lease provided.

         25.3 SURRENDER. No act or thing done by Landlord during the term hereby
demised shall be deemed an acceptance of a surrender of the Premises, and no
agreement to accept such surrender shall be valid, unless in writing signed by
Landlord. No employee of Landlord or of Landlord's agents shall have any power
to accept the keys of the Premises prior to the termination of this Lease. The
delivery of keys to any employee of Landlord or of Landlord's agents shall not
operate as a termination of the Lease or a surrender of the Premises. In the
event that Tenant at any time desires to have Landlord underlet the Premises for
Tenant's account, Landlord or Landlord's agents are authorized to receive the
keys for such purposes without releasing Tenant from any of the obligations
under this Lease, and Tenant hereby relieves Landlord of any liability for loss
of or damage to any of Tenant's effects in connection with such underletting.

26.      INABILITY TO PERFORM - EXCULPATORY CLAUSE

         Except as provided in Article 4.1, 4.2, 8.8, 18 and 20 hereof, this
Lease and the obligations of Tenant to pay rent hereunder and perform all the
other covenants, agreements, terms, provisions and conditions hereunder on the
part of Tenant to be performed shall in no way be affected, impaired or excused
because Landlord is unable to fulfill any of its obligations under this Lease or
is unable to supply or is delayed in supplying any service expressly or
impliedly to be supplied or is unable to make or is delayed in making any
repairs, replacements, additions, alterations, improvements or decorations or is
unable to supply or is delayed in supplying any equipment or fixtures if
Landlord is prevented or delayed from so doing by reason of strikes or labor
troubles or any other similar or dissimilar cause whatsoever beyond Landlord's
reasonable control, including but not limited to, governmental preemption in
connection with a national emergency or by reason of any rule, order or
regulation of any department or subdivision thereof of any governmental agency
or by reason of the conditions of supply and demand which have been or are
affected by war, hostilities or other similar or dissimilar emergency. In each
such instance of inability of Landlord to perform, Landlord shall exercise
reasonable diligence to eliminate the cause of such inability to perform.

         Tenant shall neither assert nor seek to enforce any claim against
Landlord, or Landlord's agents or employees, or the assets of Landlord or of
Landlord's agents or employees, for breach of this Lease or otherwise, other
than against Landlord's interest in the Building of which the Premises are a
part and the Complex and in the uncollected rents, issues and profits thereof,
and Tenant agrees to look solely to such interest for the satisfaction of any
liability of Landlord under this Lease, it being specifically agreed that in no
event shall Landlord or Landlord's agents or employees (or any of the officers,
trustees, directors, partners, beneficiaries, joint venturers, members,
stockholders or other principals or representatives, and the like, disclosed or
undisclosed, thereof) ever be personally liable for any such liability. This
paragraph shall not limit any right that Tenant might otherwise have to obtain
injunctive relief against Landlord or to take any other action which shall not
involve the personal liability of Landlord to respond in monetary damages from
Landlord's assets other than the Landlord's interest in said real estate, as
aforesaid. In no event shall Landlord or Landlord's agents or employees (or any
of the officers, trustees, directors, partners, beneficiaries, joint venturers,
members, stockholders or other principals or representatives and the like,
disclosed or undisclosed, thereof) ever be liable for consequential or
incidental damages. Without limiting the foregoing, in no event shall Landlord
or Landlord's agents or employees (or any of the

                                      -44-
<PAGE>   54
officers, trustees, directors, partners, beneficiaries, joint venturers,
members, stockholders or other principals or representatives and the like,
disclosed or undisclosed, thereof) ever be liable for lost profits of Tenant. If
by reason of Landlord's failure to acquire title to the real property of which
the Premises are a part or to complete construction of the Building or Premises,
Landlord shall be held to be in breach of this Lease, Tenant's sole and
exclusive remedy shall be a right to terminate this Lease.

27.      BILLS AND NOTICES

         Any notice, consent, request, bill, demand or statement hereunder by
either party to the other party shall be in writing and, if received at
Landlord's or Tenant's address, shall be deemed to have been duly given when
either delivered or served personally or mailed in a postpaid envelope,
deposited in the United States mail addressed to Landlord at its address as
stated in Exhibit 1 and to Tenant at the Premises (or at Tenant's address as
stated in Exhibit 1, if mailed prior to Tenant's occupancy of the Premises), or
if any address for notices shall have been duly changed as hereinafter provided,
if mailed as aforesaid to the party at such changed address. Either party may at
any time change the address or specify an additional address for such notices,
consents, requests, bills, demands or statements by delivering or mailing, as
aforesaid, to the other party a notice stating the change and setting forth the
changed or additional address, provided such changed or additional address is
within the United States.

         If Tenant is a partnership, Tenant, for itself, and on behalf of all of
its partners, hereby appoints Tenant's Service Partner, as identified on Exhibit
1, to accept service of any notice, consent, request, bill, demand or statement
hereunder by Landlord and any service of process in any judicial proceeding with
respect to this Lease on behalf of Tenant and as agent and attorney-in-fact for
each partner of Tenant.

         All bills and statements for reimbursement or other payments or charges
due from Tenant to Landlord hereunder shall be due and payable in full twenty
(20) days, unless herein otherwise provided, after submission thereof by
Landlord to Tenant. Tenant's failure to make timely payment of any amounts
indicated by such bills and statements, whether for work done by Landlord at
Tenant's request, reimbursement provided for by this Lease or for any other sums
properly owing by Tenant to Landlord, shall be treated as a default in the
payment of rent, in which event Landlord shall have all rights and remedies
provided in this Lease for the nonpayment of rent.

28.      PARTIES BOUND -- SEIZIN OF TITLE

         The covenants, agreements, terms, provisions and conditions of this
Lease shall bind and benefit the successors and assigns of the parties hereto
with the same effect as if mentioned in each instance where a party hereto is
named or referred to, except that no violation of the provisions of Article 16
hereof shall operate to vest any rights in any successor or assignee of Tenant
and that the provisions of this Article 28 shall not be construed as modifying
the conditions of limitation contained in Article 21 hereof.

         If, in connection with or as a consequence of the sale, transfer or
other disposition of the real estate (land and/or Building, either or both, as
the case may be) of which the Premises are a part, Landlord ceases to be the
owner of the reversionary interest in the Premises, Landlord shall be entirely
freed and relieved from the performance and observance thereafter of all
covenants and obligations hereunder on the part of Landlord to be performed and
observed, it being understood and agreed in such event (and it shall be deemed
and construed as a covenant running with the land) that the person succeeding to
Landlord's ownership of said reversionary interest shall thereupon and
thereafter assume, and perform and observe, any and all of such covenants and
obligations of Landlord.

29.      MISCELLANEOUS

         29.1 SEPARABILITY. If any provision of this Lease or portion of such
provision or the application thereof to any person or circumstance is for any
reason held invalid or unenforceable, the

                                      -45-
<PAGE>   55
remainder of the Lease (or the remainder of such provision) and the application
thereof to other persons or circumstances shall not be affected thereby.

         29.2 CAPTIONS, ETC. The captions are inserted only as a matter of
convenience and for reference, and in no way define, limit or describe the scope
of this Lease nor the intent of any provisions thereof. References to "State"
shall mean, where appropriate, the District of Columbia and other Federal
territories, possessions, as well as a state of the United States.

         29.3 BROKER. Tenant represents and warrants that it has not directly or
indirectly dealt, with respect to the leasing of office space in the Building or
any Center, Office Park or other Park of which it is a part (called "Building,
etc." in this Article 29.3) with any broker or had its attention called to the
Premises or other space to let in the Building, etc. by anyone other than the
broker, person or firm, if any, designated in Exhibit 1. Tenant agrees to
defend, exonerate and save harmless and indemnify Landlord and anyone claiming
by, through or under Landlord against any claims arising in breach of the
representation and warranty set forth in the immediately preceding sentence,
provided that Landlord shall be solely responsible for the payment of brokerage
commissions to the brokers, persons or firms, if any, designated in Exhibit 1.
Landlord represents and warrants that, in connection with the execution and
delivery of the Lease, it has not directly or indirectly dealt with any broker
other than the brokers designated on Exhibit 1. Landlord agrees to defend,
exonerate and save harmless Tenant and anyone claiming by, through, or under
Tenant against any claims arising in breach of the representation and warranty
set forth in the immediately preceding sentence.

         29.4 MODIFICATIONS. If in connection with obtaining financing for the
Building, a bank, insurance company, pension trust or other institutional lender
shall request reasonable modifications in this Lease as a condition to such
financing, Tenant will not withhold, delay or condition its consent thereto,
provided that such modifications do not increase the obligations of Tenant
hereunder or adversely affect the leasehold interest hereby created.

         29.5 ARBITRATION. Any disputes relating to provisions or obligations in
this Lease as to which a specific provision for a reference to arbitration is
made herein shall be submitted to arbitration in accordance with the provisions
of applicable state law (as identified on Exhibit 1), as from time to time
amended. Arbitration proceedings, including the selection of an arbitrator,
shall be conducted pursuant to the rules, regulations and procedures from time
to time in effect as promulgated by the American Arbitration Association. Prior
written notice of application by either party for arbitration shall be given to
the other at least ten (10) days before submission of the application to the
said Association's office in the City wherein the Building is situated (or the
nearest other city having an Association office). The arbitrator shall hear the
parties and their evidence. The decision of the arbitrator shall be binding and
conclusive, and judgment upon the award or decision of the arbitrator may be
entered in the appropriate court of law (as identified on Exhibit 1); and the
parties consent to the jurisdiction of such court and further agree that any
process or notice of motion or other application to the Court or a Judge thereof
may be served outside the State wherein the Building is situated by registered
mail or by personal service, provided a reasonable time for appearance is
allowed. The costs and expenses of each arbitration hereunder and their
apportionment between the parties shall be determined by the arbitrator in his
award or decision. No arbitrable dispute shall be deemed to have arisen under
this Lease prior to (i) the expiration of the period of twenty (20) days after
the date of the giving of written notice by the party asserting the existence of
the dispute together with a description thereof sufficient for an understanding
thereof; and (ii) where a Tenant payment (e.g., Tax Excess or Operating Expense
Excess under Article 9 hereof) is in issue, the amount billed by Landlord which
is not disputed by Tenant in good faith having been paid by Tenant.

         29.6 GOVERNING LAW. This Lease is made pursuant to, and shall be
governed by, and construed in accordance with, the laws of the State wherein the
Building is situated and any applicable local municipal rules, regulations,
by-laws, ordinances and the like.

                                      -46-
<PAGE>   56
         29.7 ASSIGNMENT OF RENTS. With reference to any assignment by Landlord
of its interest in this Lease, or the rents payable hereunder, conditional in
nature or otherwise, which assignment is made to or held by a bank, trust
company, insurance company or other institutional lender holding a mortgage or
ground lease on the Building, Tenant agrees:

                  (a) that the execution thereof by Landlord and the acceptance
thereof by such mortgagee and/or ground lessor shall never be deemed an
assumption by such mortgagee and/or ground lessor of any of the obligations of
the Landlord thereunder, unless such mortgagee and/or ground lessor shall, by
written notice sent to the Tenant, specifically otherwise elect; and

                  (b) that, except as aforesaid, such mortgagee and/or ground
lessor shall be treated as having assumed the Landlord's obligations thereunder
only upon foreclosure of such mortgagee's mortgage or deed of trust or
termination of such ground lessor's ground lease and the taking of possession of
the demised Premises after having given notice of its exercise of the option
stated in Article 23 hereof to succeed to the interest of the Landlord under
this Lease.

         29.8 REPRESENTATION OF AUTHORITY. By his execution hereof each of the
signatories on behalf of the respective parties hereby warrants and represents
to the other that he is duly authorized to execute this Lease on behalf of such
party. If Tenant is a corporation, Tenant hereby appoints the signatory whose
name appears below on behalf of Tenant as Tenant's attorney-in-fact for the
purpose of executing this Lease for and on behalf of Tenant.

         29.9 EXPENSES INCURRED BY LANDLORD UPON TENANT REQUESTS. Tenant shall,
upon demand, reimburse Landlord for all reasonable expenses, including, without
limitation, legal fees, incurred by Landlord in connection with all requests by
Tenant for consents, approvals or execution of collateral documentation related
to this Lease, including, without limitation, costs incurred by Landlord in the
review and approval of Tenant's plans and specifications in connection with
proposed alterations to be made by Tenant to the Premises, requests by Tenant to
sublet the Premises or assign its interest in the Lease, the execution by
Landlord of estoppel certificates requested by Tenant (except that there shall
be no charge for the first such estoppel certificate requested by Tenant in any
calendar year), and requests by Tenant for Landlord to execute waivers of
Landlord's interest in Tenant's property in connection with third party
financing by Tenant. Such costs shall be deemed to be additional rent under the
Lease.

         29.10 SURVIVAL. Without limiting any other obligation of the Tenant
which may survive the expiration or prior termination of the term of the Lease,
all obligations on the part of Tenant to indemnify, defend, or hold Landlord
harmless, as set forth in this Lease (including, without limitation, Tenant's
obligations under Articles 13(d), 15.3, and 29.3) shall survive the expiration
or prior termination of the term of the Lease.

                                      -47-
<PAGE>   57
         IN WITNESS WHEREOF the parties hereto have executed this Indenture of
Lease in multiple copies, each to be considered an original hereof, as a sealed
instrument on the day and year noted in Exhibit 1 as the Execution Date.

LANDLORD:                                   TENANT:
TECHNOLOGY SQUARE LLC,                      AKAMAI TECHNOLOGIES, INC.
a Delaware limited liability company

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: /s/ Thomas Ragno                  By: /s/ Paul Sagan
                 ---------------------------           -------------------------
             Name: Thomas Ragno                    Name: Paul Sagan
             Title: Senior Vice President          Title: President and Chief
                                                          Operating Officer
                                                       Hereunto Duly Authorized

         IF TENANT IS A CORPORATION, A SECRETARY'S OR CLERK'S CERTIFICATE OF THE
AUTHORITY AND THE INCUMBENCY OF THE PERSON SIGNING ON BEHALF OF TENANT SHOULD BE
ATTACHED.

COMMONWEALTH, DISTRICT OR
STATE OF

COUNTY OF

         On the Execution Date stated in Exhibit 1, the person above signing
this Lease for and on behalf of the Tenant, to me personally known, did sign and
execute this Lease and, being by me duly sworn, did depose and say that he is
the officer of the above named Tenant, as noted, and that he signed his name
hereto by order of the Board of Directors of said Tenant.

                                           -------------------------------------
                                           Notary Public
                                           My Commission Expires:_______________

COMMONWEALTH OF MASSACHUSETTS

COUNTY OF SUFFOLK

         On the Execution Date stated in Exhibit 1, the person above signing
this Lease for and on behalf of Landlord to me personally known, did sign and
execute this Lease and, being by me duly sworn, did depose and say that he is
the duly authorized representative of Landlord.

                                           -------------------------------------
                                           Notary Public
                                           My Commission Expires:_______________

                                      -48-
<PAGE>   58
                                    EXHIBIT 3

                             BUILDING STANDARD ITEMS

                              INTENTIONALLY OMITTED

                                      -49-
<PAGE>   59
                                    EXHIBIT 4

                                BUILDING SERVICES

A.     General Cleaning (Monday through Friday)

        1.      All stone, ceramic, tile, marble, terrazzo and other unwaxed
                flooring to be swept nightly, using approved dust-down
                preparation.

        2.      All wood, linoleum, vinyl-asbestos, vinyl and other similar
                types of floors to be swept or dry mopped nightly, using
                dust-down preparation; all carpeting and rugs in the main
                traffic areas (corridors, reception areas, etc.) to be vacuumed
                nightly and all other carpeted areas to be vacuumed at least
                once each week.

        3.      Wax all public areas monthly.

        4.      Hand dust all furniture, files and fixtures nightly.

        5.      Empty all waste receptacles nightly and remove waste paper and
                waste materials, including folded paper boxes and cartons, to a
                designated area.

        6.      Empty and clean all ash trays and screen all sand urns nightly.

        7.      Wash and clean all water fountains and coolers nightly. Sinks
                and floors adjacent to sinks to be washed nightly.

        8.      Hand dust all door and other ventilating louvers within reach,
                as necessary, but not less often than monthly.

        9.      Dust all telephones as necessary.

        10.     Keep lockers and janitor sink rooms in a neat, orderly condition
                at all times.

        11.     Wipe clean all bright metal work as necessary.

        12.     Check all stairwells throughout entire building nightly and keep
                in clean condition.

        13.     Metal doors and trim of all public elevator cars to be properly
                maintained and kept clean.

B.     Common Area Lavatories

        1.      Sweep and wash all lavatory floors nightly, using proper
                non-scented disinfectants.

        2.      Clean all mirrors, powder shelves, bright work and enameled
                surfaces in all lavatories nightly. Scour, wash and disinfect
                all basins, bowls and urinals using non-scented disinfectants.

        3.      Police lavatories during the day with matron or porter to pick
                up waste and replenish materials.

        4.      Wash all toilet seats nightly.

                                      -50-
<PAGE>   60
        5.      Fill toilet tissue holders nightly.

        6.      Empty paper towel receptacles nightly.

        7.      Empty sanitary disposal receptacles nightly.

        8.      Thoroughly clean all wall tile and stall surfaces as necessary.

C.     High Dusting

       Do all high dusting (not reached in nightly cleaning) quarterly which
       includes the following:

        1.      Dust all pictures, frames, charts, graphs, and similar wall
                hangings.

        2.      Dust exposed pipes, ventilation and air conditioning louvers,
                ducts and high moldings.

D.     Window Cleaning

        1.      All exterior windows (except for any retail/commercial areas)
                from the second floor and above will be cleaned inside and
                outside at least three (3) times per calendar year except when
                cleaning is rendered impracticable by inclement weather.

        2.      Entrance doors and elevator lobby glass to be cleaned daily and
                kept in a clean condition at all times during the day.

        3.      Wipe down all metal window frames as necessary but not less
                often than monthly.

E.     Building Lobbies

        1.      Floors to be swept and washed or vacuumed nightly, and machine
                scrubbed according to Building Standard frequency.

        2.      Carpeting in passenger elevator cabs to be vacuum cleaned
                nightly.

        3.      Lobby walls to be dusted as often as necessary, but not less
                than weekly.

        4.      Screen and clean sand urns nightly.

        5.      Clean all unpainted metal work in a manner appropriate to
                original finish.

F.     Porters

       Necessary number of day porters under supervision will be assigned for
       the following services:

        1.      Service all public and building operating space throughout the
                Building.

        2.      Keep elevator cars clean and neat during the day.

        3.      Maintain lobbies clean and, during wet weather, mopped dry to
                the extent practicable.

        4.      Dust and rub down all elevator doors, frames, telephone booths
                and directories daily.

                                      -51-
<PAGE>   61
        5.      Sweep sidewalks, ramps, etc. daily.

        6.      Clean roofs and setbacks as often as necessary.

        7.      Maintain firehose and equipment clean.

        8.      Lay and remove lobby runners as necessary.

        9.      Replenish toilet tissue, towels and other supplies in
                lavatories.

        10.     Maintain fan rooms, motor rooms and air conditioning rooms in
                clean condition.

        11.     Check stairways and keep same neat and clean during the day.

        12.     Clean exterior columns, exterior signs and metal work, standpipe
                and sprinkler system, walkways and stairs as necessary.

        13.     If directed by superintendent, fill towel and soap dispensers
                and perform any emergency cleaning required.

                                      -52-
<PAGE>   62
                                    EXHIBIT 5

                            FORM OF LETTER OF CREDIT

BENEFICIARY:                                            ISSUANCE DATE:

                                                        ________________, 1999

TECHNOLOGY SQUARE LLC
c/o Beacon Capital Partners                             IRREVOCABLE STANDBY
                                                        LETTER OF CREDIT NO.

ACCOUNTEE/APPLICANT:                                    MAXIMUM/AGGREGATE
                                                        CREDIT AMOUNT:
AKAMAI TECHNOLOGIES, INC.                               USD: $2,000,000.00
[TENANT]

LADIES AND GENTLEMEN:

         We hereby establish our irrevocable letter of credit in your favor for
account of the applicant up to an aggregate amount not to exceed One Million
Three Hundred Thousand and 00/100 US Dollars ($1,300,000.00) available by your
draft(s) drawn on ourselves at sight accompanied by:

         Your statement, signed by a purportedly authorized officer/official
certifying that the Beneficiary is entitled to draw upon this Letter of Credit
(in the amount of the draft submitted herewith) pursuant to Paragraph 1 of the
Rider to the Lease (the "Lease") dated July 8, 1999 by and between TECHNOLOGY
SQUARE LLC, as Landlord, and AKAMAI TECHNOLOGIES, INC., as Tenant.

         Draft(s) must indicate name and issuing bank and credit number and must
be presented at this office.

         You shall have the right to make partial draws against this Letter of
Credit, from time to time.

         Except as otherwise expressly stated herein, this Letter of Credit is
subject to the "Uniform Customs and practice for Documentary Credits,
International Chamber of Commerce, Publication No. 500 (1993 Revision)".

         This Letter of Credit shall expire at our office on ________________,
1999 (the "Stated Expiration Date"). It is a condition of this Letter of Credit
that the Stated Expiration Date shall be deemed automatically extended without
amendment for successive one (1) year periods from such Stated Expiration Date,
unless at least forty-

                                      -53-
<PAGE>   63
five (45) days prior to such Stated Expiration Date )or any anniversary thereof)
we shall notify you and the Accountee/Applicant in writing by registered mail
(return receipt) that we elect not to consider this Letter of Credit extended
for any such additional one (1) year period.

                                      -54-
<PAGE>   64
                                    EXHIBIT 6

                               BASE BUILDING WORK

The Base Building Specifications attached hereto, as modified by the following:

1.   Tenant shall have the ability to utilize the base building water
     purification system with a common building riser to each floor. Landlord
     shall be responsible for the costs to install the base building water
     purification system.

2.   Landlord's approval as it relates to the design and construction of
     Tenant's elevator lobbies shall not be unreasonably withheld.

3.   Landlord shall permit Tenant, at Tenant's sole cost and expense, to modify
     the base building drop ceiling height from 8'6" to 8'11".

4.   Landlord shall be responsible, at Landlord's sole cost and expense, for
     furnishing and installing building standard horizontal mini-blinds
     throughout the premises at completion of the Landlord's Work in the
     premises.

5.   If the base building perimeter diffusers are not available to meet Tenant's
     move-in schedule, Landlord's contractor may substitute an alternative which
     is equal in performance and quality, provided that any additional cost
     shall be the responsibility of Landlord.

6.   Tenant's fire alarm system may tie into the fire alarm riser to be located
     on each floor, and Tenant shall not be required to tie each floor back to
     the main annunciator panel on floor one, provided that final approval of
     any fire alarm design and/or installation shall be subject to the approval
     of any and all governmental authorities having jurisdiction.

                                      -55-
<PAGE>   65
                                    EXHIBIT 7

                                  EXTERIOR SIGN

         Tenant's exterior signage rights shall be for two (2) signs, located at
the top of the Building, provided that such rights can be granted to Tenant
without limiting the amount, size and location of signage permitted for the
other buildings in the Complex pursuant to the master signage plan for the
Complex currently being developed by Landlord with the City of Cambridge.

         The final design, location, and size of signs shall be subject to the
Landlord's prior written approval, which shall not be unreasonably withheld or
delayed, and shall be subject to the provisions of the first paragraph of this
Exhibit 7.

         Notwithstanding any provision of this Lease to the contrary, if and to
the extent that Landlord grants Forrester Research, Inc. the right to place
exterior signage on the second floor of its building in the Complex (or any
other floor other than the top of the building), then Landlord shall also grant
Tenant the right to a similar amount of exterior signage on the second (or
other) floor of the Building, provided that Tenant shall in any event be
responsible for obtaining all necessary permits prior to erecting such second
(or other) floor signage.

                                      -56-
<PAGE>   66
                                    EXHIBIT 8

                           TENANT'S REMOVABLE PROPERTY

1.  Antennae

2.  Satellite Dishes

3.  Network Operations Center

4.  Computer Equipment

5.  Telephone Switch and Equipment

6.  Signage (Interior and Exterior)

7.  Kitchen Equipment (Only if not built in)

8.  Security System (Only if installed by Tenant)

9.  Generators (Only if installed by Tenant in the last two (2) years of the
    lease term)

                                      -57-
<PAGE>   67
                                 RIDER TO LEASE

                         LANDLORD: Technology Square LLC
                        TENANT: Akamai Technologies, Inc.

The subject Lease is hereby amended as follows:

1.       SECURITY DEPOSIT

         Tenant acknowledges that Landlord is unwilling to execute the Lease
unless Tenant provides Landlord with security for Tenant's obligations under the
Lease as follows. Tenant shall have the right to provide such security deposit
by either providing to Landlord a security in accordance with Section I below
or, at Tenant's election, a Letter of Credit in accordance with Section II
below. Tenant shall have the right to change said election from time to time on
not less than thirty (30) days' written notice to Landlord, and Landlord shall,
upon receipt of the replacement form of security deposit in conformance with the
terms hereof, return the original form of security deposit to Tenant.

         I.       SECURITY DEPOSIT

         Tenant shall, at the time that Tenant executes and delivers this Lease
to Landlord, pay to Landlord a security deposit of Two Million and 00/100
Dollars ($2,000,000.00) securing Tenant's obligations under this Lease. In no
event shall said security deposit be deemed to be a prepayment of rent nor shall
it be considered a measure of liquidated damages. Tenant agrees that interest
shall accrue on said deposit at the then current passbook savings rate offered
by the National Bank, as defined in Article 6(a) of the Lease, provided however
that Landlord shall have no obligation to maintain such deposit in a separate
account (i.e. Landlord shall have the right to commingle such deposit with other
funds of Landlord). In the event that Tenant shall default in any of its
obligations under the Lease, beyond the expiration of applicable notice and
grace periods, Landlord shall have the right, without prior notice to Tenant, to
apply said deposit (or any portion thereof) towards the cure of any such default
and Tenant shall promptly, upon notice from Landlord, pay to Landlord any amount
so applied by Landlord in order to restore the full amount of said deposit. The
application of all or any part of the deposit to any obligation or default of
Tenant under this Lease shall not deprive Landlord of any other rights or
remedies Landlord may have nor shall such application by Landlord constitute a
waiver by Landlord. The amount of the Security Deposit shall be reduced, and the
excess thereof refunded to Tenant, if and to the extent that the Tenant would be
entitled to a reduction in the Letter of Credit Amount pursuant to Paragraph II
below. Provided that Tenant is not in default of any of its obligations under
the Lease at the expiration or earlier termination of the term of the Lease,
Landlord shall refund to Tenant any portion of said security deposit which
Landlord is then holding (less the amount determined by Landlord in good faith
to be sufficient to cure any unsatisfied obligation of Tenant) within thirty
(30) days after such expiration or earlier termination of the term. Upon receipt
of all amounts owed under the Lease, Landlord shall promptly return the balance
(if any) of any amounts so

                                      -58-
<PAGE>   68
retained by Landlord in connection with such obligations to Tenant. In addition
to any other deductions Landlord is entitled to make pursuant to the terms
hereof, Landlord shall have the right to make a good faith estimate of any
unreconciled Tax Excess and Operating Expense Excess as of the expiration or
earlier termination of the term of the Lease and to deduct any anticipated
shortfall from the Security Deposit.

                                    or

II.      LETTER OF CREDIT

         A. Tenant shall deliver to Landlord, on the date that Tenant executes
and delivers the Lease to Landlord, an Irrevocable Standby Letter of Credit
("Letter of Credit") which shall be (1) in the form attached hereto as Exhibit
5, (2) issued by issued by a bank reasonably acceptable to Landlord upon which
presentment may be made in Boston, Massachusetts, (3) in the Letter of Credit
Amount, as hereinafter defined, and (4) for a term of one (1) year, subject to
extension in accordance with the terms of the Letter of Credit. Tenant shall, on
or before the date thirty (30) days prior to the expiration of the term of such
Letter of Credit, deliver to Landlord a new Letter of Credit satisfying the
foregoing conditions ("Substitute Letter of Credit") in lieu of the Letter of
Credit then being held by Landlord. Such Letter of Credit shall be automatically
renewable in accordance with the second to last grammatical paragraph of Exhibit
5; provided that, in such event, Tenant shall be required to deliver a
Substitute Letter of Credit satisfying the conditions hereof, on or before the
date thirty (30) days prior to the expiration of the term of such Letter of
Credit, if the issuer of such Letter of Credit gives notice of its election not
to renew such Letter of Credit for any additional period pursuant thereto. Upon
written request of Tenant, Landlord shall deliver to the issuing bank an
instruction authorizing the issuing bank to reduce the Letter of Credit Amount
in accordance with the schedule set forth herein.

         B. For the purposes hereof, the "Letter of Credit Amount" shall be
defined as follows:

            1. During the Initial Period, as hereinafter defined, the Letter of
Credit Amount shall be Two Million and 00/100 Dollars ($2,000,000.00).

            2. During the Second Period, as hereinafter defined, the Letter of
Credit Amount shall be One Million Seven Hundred Fourteen Thousand Two Hundred
Eighty-Five and 71/100 Dollars ($1,714,285.71).

            3. During the Third Period, as hereinafter defined, the Letter of
Credit Amount shall be One Million Four Hundred Twenty-Eight Thousand Five
Hundred Seventy-One and 43/100 Dollars ($1,428,571.43).

                                      -59-
<PAGE>   69
            4. During the Fourth Period, as hereinafter defined, the Letter of
Credit Amount shall be One Million One Hundred Forty-Two Thousand Eight Hundred
Fifty-Seven and 14/100 Dollars ($1,142,857.14).

            5. During the Fifth Period, as hereinafter defined, the Letter of
Credit Amount shall be Eight Hundred Fifty-Seven Thousand One Hundred Forty-Two
and 86/100 Dollars ($857,142.86).

            6. During the Sixth Period, as hereinafter defined, the Letter of
Credit Amount shall be Five Hundred Seventy-One Thousand Four Hundred
Twenty-Eight and 57/100 Dollars ($571,428.57).

            7. During the Seventh Period, as hereinafter defined, the Letter of
Credit Amount shall be Two Hundred Eighty-Five Thousand Seven Hundred Fourteen
29/100 Dollars ($285,714.29).

            8. During the Eighth Period, as hereinafter defined, the Letter of
Credit Amount shall be Zero Dollars ($0).

         C. Letter of Credit Periods

         The "Initial Period" shall commence as of the initial Term Commencement
Date in respect of Portion A and shall expire as of the first anniversary of the
Term Commencement Date in respect of Portion A, provided however, that if (i)
Tenant is in monetary or material non-monetary default of any of its obligations
as of the such anniversary, (ii) the Lease is not in full force and effect as of
such anniversary, or (iii) as of such anniversary, Tenant has on more than one
occasion previously during the term of the Lease been in monetary or material
non-monetary default beyond any applicable notice and cure periods (any of (i)
through (iii) being referred to as a Failure Condition), the Initial Period
shall expire as of the first day after the first anniversary of the initial Term
Commencement Date in respect of Portion A that no Failure Conditions exist.

         Each successive Period thereafter shall commence as of the day
immediately following expiration of the immediately preceding Period and,
subject to the extension of the Period if a Failure Condition exists, shall
expire as of the next following anniversary of the Term Commencement Date in
respect of Portion A.

         D. In the event that Tenant is in default of its obligations under the
Lease, beyond the expiration of applicable notice and grace periods, then the
Landlord shall have the right, at any time after such event, without giving any
further notice to Tenant, to draw down from said Letter of Credit (Substitute
Letter of Credit or Additional Letter of Credit, as defined below, as the case
may be) (a) the amount necessary to cure such default or (b) if such default
cannot reasonably be cured by the expenditure of money, to exercise all rights
and remedies Landlord may have on account of such default, the amount which, in
Landlord's opinion, is necessary to satisfy Tenant's liability on account
thereof.

                                      -60-
<PAGE>   70
In the event of any such draw by the Landlord, Tenant shall, within fifteen (15)
business days of written demand therefor, deliver to Landlord an additional
Letter of Credit satisfying the foregoing conditions ("Additional Letter of
Credit"), except that the amount of such Additional Letter of Credit shall be
the amount of such draw. In addition, in the event of a termination based upon
the default of Tenant under the Lease, or a rejection of the Lease pursuant to
the provisions of the Federal Bankruptcy Code, Landlord shall have the right to
draw upon the Letter of Credit (from time to time, if necessary) to cover the
full amount of damages and other amounts due from Tenant to Landlord under the
Lease. Any amounts so drawn shall, at Landlord's election, be applied first to
any unpaid rent and other charges which were due prior to the filing of the
petition for protection under the Federal Bankruptcy Code.

         E. In the event that Tenant fails timely to deliver to Landlord a
Substitute Letter of Credit, then the Landlord shall have the right, at any time
after such event, without giving any further notice to Tenant or to Landlord, to
draw down the Letter of Credit (or Substitute Letter of Credit and/or Additional
Letter(s) of Credit) and to hold the proceeds thereof ("Security Proceeds") in a
segregated bank account in the name of the Landlord as security for Tenant's
obligations under the Lease in accordance with the provisions of this Paragraph
1.

         F. To the extent that Landlord has not previously drawn upon any Letter
of Credit, Substitute Letter of Credit, Additional Letter of Credit or Security
Proceeds (collectively "Collateral") held by the Landlord, and to the extent
that Tenant is not otherwise in default of its obligations under the Lease as of
the termination date of the Lease, Landlord shall return such Collateral to
Tenant on the termination of the term of the Lease.

         G. In no event shall the proceeds of any Letter of Credit be deemed to
be a prepayment of rent nor shall it be considered as a measure of liquidated
damages.

2.       TENANT'S OPTION TO EXTEND THE TERM OF THE LEASE

         A. On the conditions, which conditions Landlord may waive, at its
election, by written notice to Tenant at any time, that Tenant is not in default
of its covenants and obligations under the Lease, and that Akamai Technologies,
Inc., itself, or an Assignee or Affiliated Entity (as those terms are defined in
Article 16) collectively are occupying at least seventy percent (70%) of the
Premises then demised to Tenant, both as of the time of option exercise and as
of the commencement of the hereinafter described additional term, Tenant shall
have the option to extend the term of this Lease for one (1) additional five (5)
year term, such additional term commencing as of the expiration of the initial
term of the Lease. Tenant may exercise such option to extend by giving Landlord
written notice on or before the date twelve (12) months prior to the expiration
date of the initial term of the Lease. Upon the timely giving of such notice,
the term of this Lease shall be deemed extended upon all of the terms and
conditions of this Lease, except that Landlord shall have no obligation to
construct or renovate the Premises and that the Yearly Rent,

                                      -61-
<PAGE>   71
Operating Costs in the Base Year, and Tax Base during such additional term shall
be as hereinafter set forth. If Tenant fails to give timely notice, as
aforesaid, Tenant shall have no further right to extend the term of this Lease,
time being of the essence of this Paragraph 2.

         B. Yearly Rent

         The Yearly Rent during the additional term shall be based upon the Fair
Market Rental Value, as defined in Paragraph 3 of this Rider, as of the
commencement of the additional term, of the Premises then demised to Tenant,
provided however, that in no event shall the sum of Yearly Rent, Operating
Expense Excess and Tax Excess payable by Tenant for any twelve-(12)- month
period during the additional term be less than the sum of Yearly Rent, Operating
Expense Excess and Tax Excess payable by Tenant in respect of the
twelve-(12)-month period immediately preceding the commencement of the
additional term. Tenant shall have the right, on and after the date fifteen (15)
months prior to the expiration date of the initial term of the Lease, to request
in writing that Landlord advise Tenant of Landlord's designation of the Fair
Market Rental Value applicable during the additional term. Landlord shall,
within thirty (30) days after receipt of Tenant's request, advise Tenant in
writing of such designation of the Fair Market Rental Value.

         C. Tenant's Termination Right after the Fair Market Rental Value in
            Respect of an Additional Term is Determined.

         If Tenant has exercised its right to extend the term of the Lease in
respect of said additional term, and if Tenant, in accordance with Subparagraph
(C) of Paragraph 3 of this Rider, timely elects to arbitrate the Fair Market
Rental Value applicable to such additional term, Tenant shall have the right to
terminate the term of the Lease as follows: Tenant may exercise such right by
giving written notice to Landlord on or before the date fifteen (15) days after
the Yearly Rent for the extension term is either agreed to by the parties or is
determined by the arbitrators, as the case may be. The effective termination
date shall be twelve (12) months after Landlord receives such termination notice
from Tenant. If Tenant timely exercises such termination right, then: (i) the
Yearly Rent payable by Tenant for the period commencing as of the day after the
expiration of the then current term of the Lease through the effective
termination date shall be based upon the Fair Market Rental Value, as determined
by the arbitrators or as agreed to by the parties, as the case may be, and (ii)
Tenant shall be required to reimburse Landlord, within ten (10) days of billing
therefor, for any and all reasonable out-of-pocket expenses incurred by Landlord
in connection with the arbitration proceedings; and (iii) Landlord shall have
the right, by notice ("Landlord's Extension Notice") given to Tenant within
thirty (30) days after the receipt of Tenant's termination notice, to extend the
Term of the Lease for a period ending on the date eighteen (18) months after the
expiration of the Term, prior to any extension pursuant to Paragraph C above
("Short Extended Term"). If Landlord timely gives Landlord's Extension Notice,
then the Term of the Lease shall be automatically extended for the Short
Extended Term and the Yearly Rent during the Short Extended Term shall

                                      -62-
<PAGE>   72
be based upon the Fair Market Rental Value, as determined by the arbitrators or
as agreed to by the parties, as the case may be.

         D. Tenant shall have no further option to extend the term of the Lease
other than the one (1) additional five (5) year term herein provided.

         E. Notwithstanding the fact that upon Tenant's exercise of the herein
option to extend the term of the Lease such extension shall be self-executing,
as aforesaid, the parties shall promptly execute a lease amendment reflecting
such additional term after Tenant exercises the herein option, except that the
Yearly Rent payable in respect of such additional term, the Operating Costs in
the Base Year during such additional term, and the Tax Base during such
additional term, may not be set forth in said amendment. Subsequently, after
such Yearly Rent, Operating Costs in the Base Year, and Tax Base are determined,
the parties shall execute a written agreement confirming the same. The execution
of such lease amendment shall not be deemed to waive any of the conditions to
Tenant's exercise of its rights under this Paragraph 2, unless otherwise
specifically provided in such lease amendment.

3.       DEFINITION OF FAIR MARKET RENTAL VALUE

         For the purposes of this Rider:

         A. "Fair Market Rental Value" shall be computed as of the date in
question at the then current annual rental charge (i.e., the sum of Yearly Rent
plus escalation and other charges), including provisions for subsequent
increases and other adjustments for leases or agreements to lease then currently
being negotiated, or executed in comparable space located in the Complex, or if
no leases or agreements to lease are then currently being negotiated or executed
in the Complex, the Fair Market Rental Value shall be determined by reference to
leases or agreements to lease then currently being negotiated or executed for
comparable space located elsewhere in first-class office buildings located in
East Cambridge, Massachusetts. In determining Fair Market Rental Value, the
following factors, among others, shall be taken into account and given effect:
size, location of Premises, lease term, condition of building, economic
concessions then being granted by the landlord, the absence of certain costs to
be incurred by landlord (e.g., brokerage commissions, tenant improvement costs),
and services provided by the landlord.

         B. Notwithstanding anything to the contrary herein contained, the
parties hereby agree that upon the determination of any Fair Market Rental
Value, Landlord shall have the right, exercisable by written notice to Tenant on
or before the time that Landlord gives Tenant its initial designation of Fair
Market Rental Value:

                  (1)      to change Operating Costs in the Base Year as stated
                           on Exhibit 1 from the amount stated on Exhibit 1 to
                           an amount equal to the actual amount of Operating
                           Costs for the immediately preceding Operating Year,
                           and

                                      -63-
<PAGE>   73
                  (2)      to change the Tax Base as stated on Exhibit 1 from
                           the amount stated on Exhibit 1 to an amount equal to
                           the actual amount of Taxes for the immediately
                           preceding fiscal/tax year for which Landlord has
                           actual data.

            If Landlord shall exercise such right, the amount of Yearly Rent
payable hereunder shall be commensurately adjusted to reflect such change in
Operating Costs in the Base Year and in Tax Base.

         C. Dispute as to Fair Market Rental Value

            Landlord shall initially designate Fair Market Rental Value and
Landlord shall furnish data in support of such designation. If Tenant disagrees
with Landlord's designation of a Fair Market Rental Value, Tenant shall have the
right, by written notice given within thirty (30) days after Tenant has been
notified of Landlord's designation, to submit such Fair Market Rental Value to
arbitration. Fair Market Rental Value shall be submitted to arbitration as
follows: Fair Market Rental Value shall be determined by impartial arbitrators,
one to be chosen by the Landlord, one to be chosen by Tenant, and a third to be
selected, if necessary, as below provided. The unanimous written decision of the
two first chosen, without selection and participation of a third arbitrator, or
otherwise, the written decision of a majority of three arbitrators chosen and
selected as aforesaid, shall be conclusive and binding upon Landlord and Tenant.
Landlord and Tenant shall each notify the other of its chosen arbitrator within
ten (10) days following the call for arbitration and, unless such two
arbitrators shall have reached a unanimous decision within thirty (30) days
after their designation, they shall so notify the President of the Boston Bar
Association (or such organization as may succeed to said Boston Bar Association)
and request him to select an impartial third arbitrator, who shall be a real
estate broker with at least ten (10) years' experience dealing with like types
of properties in the Cambridge office market, to determine Fair Market Rental
Value as herein defined. Such third arbitrator and the first two chosen shall,
subject to commercial arbitration rules of the American Arbitration Association,
hear the parties and their evidence and render their decision within thirty (30)
days following the conclusion of such hearing and notify Landlord and Tenant
thereof. Landlord and Tenant shall bear the expense of the third arbitrator (if
any) equally. The decision of the arbitrator shall be binding and conclusive,
and judgment upon the award or decision of the arbitrator may be entered in the
appropriate court of law (as identified on Exhibit 1); and the parties consent
to the jurisdiction of such court and further agree that any process or notice
of motion or other application to the Court or a Judge thereof may be served
outside the State wherein the Building is situated by registered mail or by
personal service, provided a reasonable time for appearance is allowed. If the
dispute between the parties as to a Fair Market Rental Value has not been
resolved before the commencement of Tenant's obligation to pay rent based

                                      -64-
<PAGE>   74
upon such Fair Market Rental Value, then Tenant shall pay Yearly Rent and other
charges under the Lease in respect of the Premises in question based upon the
rate in effect immediately before the commencement of Tenant's obligation to pay
rent based upon such Fair Market Rental Value until either the agreement of the
parties as to the Fair Market Rental Value, or the decision of the arbitrators,
as the case may be, at which time Tenant shall pay any underpayment of rent and
other charges to Landlord, or Landlord shall refund any overpayment of rent and
other charges to Tenant, in either case with interest at the rate set forth in
Article 6 hereof.

4.       ANTENNA AREA

         Tenant shall have the right to use the Antenna Area, as hereinafter
defined, to install a satellite dish and/or antenna (collectively, the
"Antenna") for a period commencing as of the date that Tenant installs the
Antenna, as hereinafter defined, in the Antenna Area ("Term Commencement Date in
respect of the Antenna Area") and terminating as of the expiration or earlier
termination of the term of the Lease. The "Antenna Area" shall be an area on the
roof of the Building containing approximately 50 square feet of rentable area in
an area to be designated by Landlord. Tenant shall be permitted to use the
Antenna Area solely for one (1) Antenna installed in accordance with
specifications approved by Landlord in advance utilizing a frequency or
frequencies and transmission power identified in such approved specifications
which Tenant will be installing in the Antenna Area and no other frequencies or
transmission power shall be used by Tenant without Landlord's prior written
consent, which shall not be unreasonably withheld or delayed, except for matters
of aesthetics, which shall be determined in Landlord's sole discretion. Such
installation shall be designed in such manner as to be easily removable and so
as not to damage the roof of the Building. The Antenna and any replacement shall
be subject to Landlord's approval, which shall not be unreasonably withheld or
delayed, except for matters of aesthetics, which shall be determined in
Landlord's sole discretion. Tenant's use of the Antenna Area shall be upon all
of the conditions of the Lease, except as follows:

         A. Tenant shall have no obligation to pay Yearly Rent, Tax Excess or
Operating Expense Excess in respect of the Antenna Area.

         B. Landlord shall have no obligation to provide any services to the
Antenna Area.

         C. Tenant shall have no right to make any changes, alterations, signs,
decoration, or other improvements (which changes, alterations, signs, decoration
or other improvements, together with the Antenna, are hereby collectively
referred to as "Rooftop Installations") to the Antenna Area or to the Antenna
without Landlord's prior written consent, which consent shall not be
unreasonably withheld or delayed, except for matters of aesthetics, which shall
be determined in Landlord's sole discretion.

         D. Landlord shall provide Tenant with 24-hour access to the Antenna
Area, subject to Landlord's reasonable security procedures and restrictions
based on emergency conditions and to other causes beyond Landlord's reasonable
control. Tenant shall give Landlord reasonable advance written notice of the
need for access to the Antenna Area

                                      -65-
<PAGE>   75
(except that such notice may be oral in an emergency), and Landlord must be
present during any entry by Tenant onto the Antenna Area. Each notice for access
shall be in the form of a work order referencing the lease and describing, as
applicable, the date access is needed, the name of the contractor or other
personnel requiring access, the name of the supervisor authorizing the
access/work, the areas to which access is required, the Building common elements
to be impacted (risers, electrical rooms, etc.) and the description of new
equipment or other Rooftop Installations to be installed and evidence of
Landlord's approval thereof. In the event of an emergency, such notice shall
follow within five (5) days after access to the Antenna Area.

         E. At the expiration or prior termination of Tenant's right to use the
Antenna Area, Tenant shall remove all Installations (including, without
limitation, the Antenna) from the Antenna Area.

         F. Tenant shall be responsible for the cost of repairing any damage to
the roof of the Building caused by the installation or removal of any Rooftop
Installations.

         G. Tenant shall have no right to sublet the Antenna Area, except in
connection with an assignment or sublease permitted hereunder or otherwise
approved by Landlord in accordance with the terms hereof.

         H. No other person, firm or entity (including, without limitation,
other tenants, licensees or occupants of the Building) shall have the right to
benefit from the services provided by the Antenna other than Tenant.

         I. In the event that Landlord performs repairs to or replacement of the
roof, Tenant shall, to the extent reasonably required, at Tenant's cost, remove
the Antenna until such time as Landlord has completed such repairs or
replacements. Tenant recognizes that there may be an interference with Tenant's
use of the Antenna in connection with such work. Landlord shall use reasonable
efforts to complete such work as promptly as possible and to perform such work
in a manner which will minimize or, if reasonably possible, eliminate any
interruption in Tenant's use of the Antenna.

         J. Any services required by Tenant in connection with Tenant's use of
the Antenna Area or the Antenna shall be installed by Tenant, at Tenant's
expense, subject to Landlord's prior approval.

         K. To the maximum extent permitted by law, all Rooftop Installations in
the Antenna Area shall be at the sole risk of Tenant, and Landlord shall have no
liability to Tenant in the event that any Rooftop Installations are damaged for
any reason, except to the extent caused by the gross negligence or willful
misconduct of Landlord, its agents or contractors.

         L. Tenant shall take the Antenna Area "as-is" in the condition in which
the Antenna Area is in as of the Commencement Date in respect of the Antenna
Area.

                                      -66-
<PAGE>   76
         M. Tenant shall comply with all applicable laws, ordinances and
regulations in Tenant's use of the Antenna Area and the Antenna.

         N Landlord shall have the right, upon thirty (30) days notice to
Tenant, to require Tenant to relocate the Antenna Area to another area
("Relocated Rooftop Area") on the roof of the Building suitable for the use of
Rooftop Installations. In such event, Tenant shall, at Landlord's cost and
expense, on or before the thirtieth (30th) day after Landlord gives such notice,
relocate all of its Rooftop Installations from the Antenna Area to the
Relocation Rooftop Area.

         O In addition to complying with the applicable construction provisions
of the Lease, Tenant shall not install or operate Rooftop Installations in any
portion of the Antenna Area until (x) Tenant shall have obtained Landlord's
prior written approval, which approval will not be unreasonably withheld or
delayed, of Tenant's plans and specifications for the placement and installation
of the Rooftop Installations in the Premises, and (y) Tenant shall have obtained
and delivered to Landlord copies of all required governmental and
quasi-governmental permits, approvals, licenses and authorizations necessary for
the lawful installation, operation and maintenance of the Rooftop Installations.
The parties hereby acknowledge and agree, by way of illustration and not
limitation, that Landlord shall have the right to withhold its approval of
Tenant's plans and specifications hereunder, and shall not be deemed to be
unreasonable in doing so, if Tenant's intended placement or method of
installation or operation of the Rooftop Installations (i) may subject other
licensees, tenants or occupants of the Building, or other surrounding or
neighboring landowners or their occupants, to signal interference, Tenant hereby
acknowledging that a shield may be required in order to prevent such
interference, (ii) does not minimize to the fullest extent practicable the
obstruction of the views from the windows of the Building that are adjacent to
the Rooftop Installations, if any, (iii) does not complement (in Landlord's sole
judgment, which shall not, however, require Tenant to incur unreasonable
expense) the design and finish of the Building, (iv) may damage the structural
integrity of the Building or the roof thereof, or (v) may constitute a violation
of any consent, approval, permit or authorization necessary for the lawful
installation of the Rooftop Installations.

         P In addition to the indemnification provisions set forth in the Lease
which shall be applicable to the Antenna Area, Tenant shall, to the maximum
extent permitted by law, indemnify, defend, and hold Landlord, its agents,
contractors and employees harmless from any and all claims, losses, demands,
actions or causes of actions suffered by any person, firm, corporation, or other
entity arising from Tenant's use of the Antenna Area.

         Q Landlord shall have the right to designate or identify the Rooftop
Installations with or by a lease or license number (or other marking) and to
place such number (or marking) on or near such Rooftop Installations.

                                      -67-
<PAGE>   77
         R. (i) Tenant recognizes that Landlord may wish to (and Landlord hereby
reserves the right to) install a central Building system (the "Central Building
System") capable of, among other things, providing Tenant with the type of
service (to be) provided by Tenant's Rooftop Installations. If Landlord elects
to install the Central Building System, and provided that such Central Building
System is capable of providing service comparable to that provided by Tenant's
Rooftop Installations, (i) Tenant shall, upon Landlord's request and at Tenant's
expense, remove its Rooftop Installations and other Alterations (including any
existing cabling) from the Building and repair any damage caused their
installation or removal, (ii) Tenant may, at Tenant's expense and subject to the
provisions of this Agreement (including, without limitation, subparagraph P
hereof), have access to and use (and tie into) the Central Building System for
the uses permitted hereunder, and (ii) commencing upon Tenant's use of the
Central Building System and continuing thereafter throughout the term, the
Yearly Rent payable hereunder shall be adjusted to be that which is reasonably
designated by Landlord from time to time based upon Landlord's determination of
the fair market value of the access rights to the Central Building System
granted herein.

            (ii) Landlord shall maintain, repair or replace the Central Building
System, in accordance with the standards for the repair and maintenance of such
systems generally prevailing in the industry from time to time, so as to
eliminate any material interruption or other adverse effects caused by
malfunction, damage or destruction of the Central Building System, the cost of
which shall be borne by Tenant if the problem was caused by the act or omission
of Tenant or its agents, contractors or employees. Notwithstanding the
foregoing, Landlord's obligation to maintain, repair or replace the Central
Building System shall apply only to the extent necessary to reach premises in
the Building that are then used by tenants after the malfunction, damage or
destruction or that, if damaged or destroyed, will be again used by tenants upon
the completion of restoration or repair thereof. In no event shall Tenant have
any claim or right to make any claim against Landlord whatsoever for any
damages, including, without limitation, consequential or incidental damages, or
lost profits, in any such circumstance.

5.       GENERATOR AREA

         Landlord hereby demises and leases to Tenant, and Tenant hereby hires
and takes from Landlord, an area containing approximately 200 square feet of
rentable area on that portion of the roof of the Building directly on top of the
ninth floor of the Building ("Generator Area") for a generator for emergency use
only ("Generator") for a term commencing as of the date of installation of the
Generator ("Term Commencement Date in respect of the Generator") and terminating
as of the expiration or earlier termination of the term of the Lease. Said
demise of the Generator Area shall be upon all of the same terms and conditions
of the Lease, except as set forth in this Paragraph 5. Tenant shall not install
or operate the Generator until Tenant has obtained and submitted to Landlord
copies of all required governmental permits, licenses, and authorizations
necessary for the installation and operation of the Generator. In addition,
Tenant shall comply with all reasonable construction rules and regulations
promulgated by Landlord in the installation,

                                      -68-
<PAGE>   78
maintenance and operation of the Generator. Tenant shall be permitted to use the
Generator Area solely for the maintenance and operation of the Generator, and
the Generator and Generator Area are solely for the benefit of Tenant. All
electricity generated by the Generator may only be consumed by Tenant in the
Premises.

         A. Tenant shall have no obligation to pay Yearly Rent, Tax Excess or
Operating Expense Excess in respect of the Generator Area.

         B. Landlord shall have no obligation to provide any services including,
without limitation, electric current, to the Generator Area.

         C. Tenant shall have no right to make any changes, alterations,
additions, decorations or other improvements (collectively "Installations") to
the Generator Area without Landlord's prior written consent, , which shall not
be unreasonably withheld or delayed, except for matters of aesthetics, which
shall be determined in Landlord's sole discretion.

         D. Tenant shall be responsible for the cost of repairing any damage to
the Building, or the cost of any necessary improvements to the Building, caused
by or as a result of the installation of the Generator and/or any Installations.

         E. Tenant shall have no right to sublet the Generator Area or to assign
its interest hereunder, except in connection with an assignment or sublease
permitted hereunder or otherwise approved by Landlord in accordance with the
terms hereof.

         F. To the maximum extent permitted by law, the Generator and all
Installations in the Generator Area shall be at the sole risk of Tenant, and
Landlord shall have no liability to Tenant in the event that the Generator or
any Installations are damaged for any reason, except to the extent caused by the
gross negligence or willful malfeasance of Landlord, its agents or contractors.

         G. Tenant shall take the Generator Area "as-is" in the condition in
which the Generator Area is in as of the Term Commencement Date in respect of
the Generator, without any obligation on the part of Landlord to prepare or
construct the Generator Area for Tenant's use or occupancy. Without limiting the
foregoing, Landlord makes no warranties or representations to Tenant as to the
suitability of the Generator Area for the installation and operation of the
Generator.

         H. In addition to and without limiting Tenant's obligations under the
Lease, Tenant shall comply with all applicable environmental and fire prevention
laws, ordinances and regulations in Tenant's use of the Generator Area.

         I. In addition to and without limiting Tenant's obligations under the
Lease, Tenant covenants and agrees that the installation and use of the
Generator and Installations shall not adversely affect the insurance coverage
for the Building. If for any

                                      -69-
<PAGE>   79
reason, the installation or use of the Generator and/or the Installations shall
result in an increase in the amount of the premiums for such coverage, then
Tenant shall be liable for the full amount of any such increase.

         J. Tenant shall, at Tenant's sole cost and expense, repair and maintain
the Generator and Installations.

         K. In addition to and without limiting the insurance provisions of the
Lease, Tenant shall procure, keep in force and pay for Commercial General
Liability Insurance in respect of the Generator Area of not less than Ten
Million ($10,000,000.00) Dollars in the event of personal injury to any number
of persons or damage to property, arising out of any one occurrence and such
insurance shall name Landlord as an additional insured party.

         L. In addition to and without limiting the indemnification provisions
set forth in the Lease, Tenant shall, to the maximum extent permitted by law,
indemnify, defend, and hold Landlord harmless from any and all claims, losses,
demands, actions, or causes of actions suffered by any person, firm,
corporation, or other entity arising from Tenant's use of the Generator Area.

         M. Notwithstanding anything to the contrary herein or in the Lease
contained, in the event that at any time during the term of the Lease in respect
of the Generator Area, Landlord determines, in its sole but bona fide business
judgment, that the periodic testing of the Generator interferes with the
operation of the Building or the operations of any of the occupants of the
Building, then Tenant shall, upon notice from Landlord, cause all further
testing of the Generator to occur after normal business hours. Other than for
periodic testing as aforesaid, in no event shall Tenant be entitled to operate
the Generator except in cases of a power outage to the Premises or any portion
thereof.

                                      -70-
<PAGE>   80
                   REVISED EXHIBIT 1, FIRST AMENDMENT, SHEET 1
                                Building No. 575
                                TECHNOLOGY SQUARE
                            Cambridge, Massachusetts

                                   LEASE DATA

Execution Date:   December 1, 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

Existing
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
<PAGE>   81
                   REVISED EXHIBIT 1, FIRST AMENDMENT, SHEET 2
                                Building No. 575
                                TECHNOLOGY SQUARE
                            Cambridge, Massachusetts

                    Tenant: AKAMAI TECHNOLOGIES, INC.
                    Execution Date: December 2, 1999

                       the Premises. The second (2nd) and seventh (7th) floors
                       of the 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.

First Amendment
Additional Premises:   First Floor Premises:

                       An area on the first (1st) floor of the Building,
                       substantially as shown on Lease Plan, Exhibit 2, First
                       Amendment

                       Tenth Floor Premises:

                       An area on the tenth (10th) floor of the Building,
                       substantially as shown on Lease Plan, Exhibit 2, First
                       Amendment

                       Basement Premises:

                       An area on the basement floor of the Building,
                       substantially as shown on Lease Plan, Exhibit 2, First
                       Amendment

                       The First Floor Premises, the Tenth Floor Premises and
                       the Basement Premises are collectively referred to herein
                       as the First Amendment Additional Premises.

Art. 3.1               Specified Commencement Date in respect of:
                          Portion A:                January 18, 2000
                          Portion B:                June 1, 2000
                          First Amendment
                          Additional Premises:      March 7, 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
                                    First Floor Premises:     December 31, 1999
                                    Basement Premises:        January 14, 2000

                                      -2-
<PAGE>   82
                   REVISED EXHIBIT 1, FIRST AMENDMENT, SHEET 3
                                Building No. 575
                                TECHNOLOGY SQUARE
                            Cambridge, Massachusetts

                    Tenant: AKAMAI TECHNOLOGIES, INC.
                    Execution Date: December 2, 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>                 <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>               <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>

                    First Amendment Additional Premises:

                    First Floor Premises:

<TABLE>
<CAPTION>
                      Time Period              Yearly Rent       Monthly Payment
<S>                   <C>                      <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).

                                      -3-
<PAGE>   83
                   REVISED EXHIBIT 1, FIRST AMENDMENT, SHEET 4
                                Building No. 575
                                TECHNOLOGY SQUARE
                            Cambridge, Massachusetts

                    Tenant: AKAMAI TECHNOLOGIES, INC.
                    Execution Date: December 2, 1999

                  Term Commencement Date
                  in respect of First Amendment
                  Additional Premises -
                  end of Lease Year 2:        $241,950.00    $20,162.50

                  Lease Years 3 - 4:          $251,628.00    $20,969.00

                  Lease Years 5 - 7:          $264,531.96    $22,044.33

                  Tenth Floor Premises:

                     Time Period                   Yearly Rent   Monthly Payment

                     Term Commencement Date
                     in respect of First Amendment
                     Additional Premises -
                     end of Lease Year 7:           $7,200.00          $600.00

                  Basement Premises:

                     Time Period                    Yearly Rent  Monthly Payment

                     Term Commencement Date
                     in respect of First Amendment
                     Additional Premises -
                     end of Lease Year 7:           $27,500.00   $2,291.67

Art. 7               Total Rentable Area of the Premises:

                            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

                                      -4-
<PAGE>   84
                   REVISED EXHIBIT 1, FIRST AMENDMENT, SHEET 5
                                Building No. 575
                                TECHNOLOGY SQUARE
                            Cambridge, Massachusetts

                    Tenant: AKAMAI TECHNOLOGIES, INC.
                    Execution Date: December 2, 1999

                                              second (2nd) and
                                              seventh (7th) floors)

                    First Amendment
                    Additional Premises:

                       First Floor Premises:  6,452 square feet

                       Tenth Floor Premises:  480 square feet

                       Basement Premises:     1,375 square feet

                     Total First Amendment
                     Additional Premises:     8,307 square feet  (Note:  the
                                              Tenth Floor Premises are not
                                              provided with any Landlord
                                              services, so they are not included
                                              in the calculations for Tenant's
                                              Share of Operating Expense Excess
                                              or Tax Excess)

                     Total Rentable Area of the Building:    173,584 square feet

                     Initial Total Rentable Area of the Complex:  532,279 square
                                                                  feet

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:                 41.13%(2)
                                Portion B:                 20.56%
                                First Amendment
                                Additional Premises:         4.51%

                                      -5-
<PAGE>   85
                   REVISED EXHIBIT 1, FIRST AMENDMENT, SHEET 6
                                Building No. 575
                                TECHNOLOGY SQUARE
                            Cambridge, Massachusetts

                    Tenant: AKAMAI TECHNOLOGIES, INC.
                    Execution Date: December 2, 1999

                           Note:    Tenant's Building Operating Cost
                                    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.

                      Tenant's Complex Operating Cost Percentage in respect of:
                           Portion A:                 13.41%(2)
                           Portion B:                   6.71%
                           First Amendment
                           Additional Premises:         1.47%
                           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:                   41.13%(2)
                          Portion B:                    20.56%
                          First Amendment
                          Additional Premises:           4.51%

                      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.

                                      -6-
<PAGE>   86
                   REVISED EXHIBIT 1, FIRST AMENDMENT, SHEET 7
                                Building No. 575
                                TECHNOLOGY SQUARE
                            Cambridge, Massachusetts

                    Tenant: AKAMAI TECHNOLOGIES, INC.
                    Execution Date: December 2, 1999

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

                    Tenant's Complex Tax Percentage in respect of:
                         Portion A:                    13.41%(2)
                         Portion B:                      6.71%
                         First Amendment
                         Additional Premises:            1.47%
                         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 September
                                          22, 1999 and Lease Plan, Exhibit 2,
                                          First Amendment, dated December 1,
                                          1999, Sheets 1 and 2

                                      -7-
<PAGE>   87
                   REVISED EXHIBIT 1, FIRST AMENDMENT, SHEET 8
                                Building No. 575
                                TECHNOLOGY SQUARE
                            Cambridge, Massachusetts

                    Tenant: AKAMAI TECHNOLOGIES, INC.
                    Execution Date: December 2, 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: ________________

                                      -8-
<PAGE>   88
                                Building No. 575
                                Technology Square
                            Cambridge, Massachusetts
                                ("the Building")

                                 FIRST AMENDMENT
                                December 1, 1999

                  LANDLORD:              Technology Square LLC

                  TENANT:                Akamai Technologies, Inc.

                  EXISTING 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 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,
                                         substantially as shown on Lease Plan
                                         Exhibit 2, Sheets 1, 2, 3, 4, 5 and 6,
                                         dated September 22, 1999

ORIGINAL
LEASE             LEASE
DATA              EXECUTION
                  DATE:                  September 22, 1999

                  TERMINATION
                  DATE:                  Seven (7) years after the Term
                                         Commencement Date in respect of Portion
                                         A

                  PREVIOUS
                  LEASE
                  AMENDMENTS:            None

                                      -1-
<PAGE>   89
FIRST AMENDMENT
ADDITIONAL
PREMISES:

         First Floor Premises:

                  An area on the first (1st) floor of the Building, consisting
                  of 6,452 square feet of Total Rentable Area, substantially as
                  shown on Lease Plan, Exhibit 2, First Amendment, Sheet 1 dated
                  December 1, 1999, a copy of which is attached hereto and
                  incorporated by reference herein

         Tenth Floor Premises:

                  An area on the tenth (10th) floor of the Building, consisting
                  of 480 square feet of Total Rentable Area, substantially as
                  shown on Lease Plan, Exhibit 2, First Amendment, Sheet 2 dated
                  December 1, 1999, a copy of which is attached hereto and
                  incorporated by reference herein

         Basement Premises:

                  An area on the basement floor of the Building, consisting of
                  1,375 square feet of Total Rentable Area, substantially as
                  shown on Lease Plan, Exhibit 2, First Amendment, Sheet 3 dated
                  December 1, 1999, a copy of which is attached hereto and
                  incorporated by reference herein

         The First Floor Premises, the Tenth Floor Premises and the Basement
         Premises are collectively referred to herein as the First Amendment
         Additional Premises.

         WHEREAS, Tenant desires to lease additional premises located in the
Building, to wit, the First Amendment Additional Premises;

         WHEREAS, Landlord is willing to lease the First Amendment Additional
Premises to Tenant on the terms and conditions hereinafter set forth;

         NOW THEREFORE, the parties hereby agree that the above-referenced lease
(the "Lease") is hereby amended as follows:

                                      -2-
<PAGE>   90
         1.       DEMISE OF THE FIRST AMENDMENT ADDITIONAL PREMISES

         Landlord hereby demises and leases to Tenant, and Tenant hereby hires
and takes from Landlord, the First Amendment Additional Premises for a term
commencing as of the Term Commencement Date in respect of First Amendment
Additional Premises, as hereinafter defined. Said demise of the First Amendment
Additional Premises shall be upon the terms set forth on Revised Exhibit 1,
First Amendment, Sheets 1, 2, 3 and 4, dated December 1, 1999, a copy of which
is attached hereto and incorporated by reference herein, and upon all of the
other terms and conditions of the Lease in respect of Portion A (including,
without limitation, Tenant's option to extend the term of the Lease, pursuant to
Paragraph 2 of the Rider to the Lease), except as follows:

         A. The Specified Commencement Date in respect of the First Amendment
Additional Premises shall be March 7, 2000.

         B. The Term Commencement Date in respect of the First Amendment
Additional Premises shall be defined as the earlier of: (i) the date as of which
the First Amendment Work, as defined in Paragraph 2 hereof, is substantially
complete, other than the installation of the stairway between the first and
second floors, and those items of the First Amendment Work which cannot
practicably be completed prior to the installation of said stairway (such as,
for example, the installation of carpeting in the immediate vicinity of such
stairway) or which are delayed as a result of the installation of the stairway,
or (ii) the date that Tenant first takes possession of the First Amendment
Premises, or any portion thereof, for use as set forth on Revised Exhibit 1.
Landlord agrees to use good faith efforts to complete those portions of the
First Amendment Work which are not complete as of the Term Commencement Date in
respect of the First Amendment Additional Premises promptly after such date.

         C. In the event that any of the provisions of the Lease are
inconsistent with this Amendment or the state of facts contemplated hereby, the
provisions of this Amendment shall control.

         2.       LANDLORD'S WORK IN RESPECT OF FIRST AMENDMENT ADDITIONAL
                  PREMISES

         Landlord shall perform the work shown on Tenant's final approved plans
with respect to the First Amendment Additional Premises ("First Amendment
Work"). The First Amendment Work shall be performed in accordance with the
provisions of the Lease applicable to the performance of Landlord's Work with
respect to Portion A (the parties hereby agreeing that the First Amendment
Additional Premises shall be deemed to be a separate Portion of the Premises,
for the purposes of Article 4 of the Lease), except that:

         A. Articles 4.1(b) and 4.1(c) of the Lease shall have no applicability
to the First Amendment Additional Premises or the performance of the First
Amendment Work, except that if Tenant exercises its right, pursuant to Article
4.1(c) to terminate the Lease

                                      -3-
<PAGE>   91
based upon the failure of the Term Commencement Date to occur on or before the
Outside Target Date, as defined in Article 4.1(c), then the term of the Lease in
respect of the First Amendment Additional Premises shall terminate as of the
effective termination date of the Lease pursuant to said Article 4.1(c)
("Effective Termination Date"); and

         B. The Final Plans Date with respect to the First Floor Premises shall
be December 31, 1999, and the Final Plans Date with respect to the Basement
Premises shall be January 14, 2000. Tenant has submitted progress prints of the
plans for the First Floor Premises to Landlord. Landlord agrees to review the
plans submitted by Tenant and to comment thereon within three (3) business days
of Landlord's receipt thereof;

         C. Landlord's Contribution in respect of the First Floor Premises shall
be up to Thirty Dollars ($30.00) per square foot of Total Rentable Area of the
First Floor Premises. There shall be no Landlord's Contribution in respect of
the Tenth Floor Premises or the Basement Premises; and

         D. Landlord and Tenant acknowledge that the Tenth Floor Premises shall
be used for the purpose set forth in Revised Exhibit 1, First Amendment, and
that no Landlord services other than lights, heat and elevator service (Tenant
acknowledging that only one elevator serves the Tenth Floor Premises) shall be
provided thereto, and that no Operating Expense Excess or Tax Excess shall be
payable with respect to the Tenth Floor Premises.

         3.       REVISED EXHIBIT 1, FIRST AMENDMENT

         Exhibit 1, Sheets 1, 2, 3, 4 and 5 dated September 22, 1999 is hereby
deleted in its entirety and Revised Exhibit 1, First Amendment, Sheets 1, 2, 3,
4 and 5 dated December 1, 1999 shall be substituted in its place.

         4.       REMEASUREMENT OF BUILDING AND COMPLEX

         The parties hereby agree that the Total Rentable Area of the Building
and the Initial Total Rentable Area of the Complex shall be revised as follows:

         A.       The Total Rentable Area of the Building is 173,584 square
                  feet.

         B.       The Initial Total Rentable Area of the Complex is 532,279
                  square feet.

         5.       SHOWERS AND LOCKERS

         Landlord acknowledges that Tenant shall have the right, in common with
others entitled thereto and subject to such rules and regulations as Landlord
may from time to time promulgate with respect thereto, to use the showers and
locker room located in the Basement of the Building, as the same may be changed
by Landlord from time to time in

                                      -4-
<PAGE>   92
accordance with the terms of the Lease, without charge, except that the costs of
maintaining and operating such facilities may be included in Operating Expenses.

         6. Reference is made to the fact that Landlord is constructing a
lavatory on the First Floor of the Building. Landlord hereby agrees that (i) the
lavatory shall be for the exclusive use of Tenant, (ii) the only door to the
lavatory shall open into the First Floor Premises, (iii) Landlord shall not add
any other door to the lavatory, (iv) no tenant or occupant of the Building other
than Tenant shall have any right to access or use the lavatory, and (v) there
shall be no adjustment of Tenant's rent or Tenant's share of operating expenses
or taxes for the building or the Complex as a result of Tenant's exclusive right
to use the lavatory as aforesaid. Without limiting the foregoing, if Landlord
determines that it is necessary to provide other tenants or occupants with a
lavatory on the First Floor of the Building (whether to comply with any
applicable law or for any other reason) then Landlord shall construct a separate
lavatory for such tenants and occupants. Tenant agrees that all of its
obligations concerning repairs, maintenance, cleaning, insurance and indemnity
which apply to the First Floor Premises shall also apply to such lavatory.

         7. As hereby amended, the Lease is ratified, confirmed and approved in
all respects.

                                      -5-
<PAGE>   93
    EXECUTED under seal as of the date first above-written.

LANDLORD:                                            TENANT:
TECHNOLOGY SQUARE LLC,                               AKAMAI TECHNOLOGIES, INC.
a Delaware limited liability company

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: /s/ Thomas Ragno                      By: /s/ Paul Sagan
        ----------------------------              ---------------------------
        Name: Thomas Ragno                        Name: Paul Sagan
        Title: Senior Vice President              Title: President
                                                  Hereunto Duly Authorized

Date Signed: January 25, 2000                     Date Signed: January 18, 2000
             ----------------                                  ----------------

                                      -6-<PAGE>   1
                                                                     Exhibit 10A

                           NATIONAL DENTEX CORPORATION
                         526 BOSTON POST ROAD, SUITE 207
                                WAYLAND, MA 01778

PERSONAL AND CONFIDENTIAL

February 16, 2000

Mr. Thomas E. Gildersleeve
12 Hudson Street
Natick, Massachusetts 01760

Dear Tom:

This letter will confirm certain agreements and understandings we have reached
in conjunction with termination of your employment with National Dentex
Corporation (the "Company"), effective December 13, 1999, as follows:

1.       As consideration for this Agreement, the Company will make four
         severance payments to you. The first payment was made on December 24,
         1999 in the amount of $3,846. The next three payments will each be in
         the amount of $8,750 (less applicable withholding) and will be made on
         February 14, 2000, February 29, 2000, and March 31, 2000, respectively.
         In addition, the Company will pay you $77,400 (less applicable
         withholding) as payment of the amounts due to you under the Company's
         Key Employee & Corporate Support Group Incentive Compensation Plan 1999
         at the same time as payments are made to other participants under the
         Plan.
2.       The last date of your employment is recognized as December 13, 1999 for
         purposes of vesting under your stock options. You may exercise any
         vested options within ninety (90) days after such date.

3.       You hereby confirm and agree that you have returned to the Company all
         documents and equipment belonging to the Company including, but not
         limited to, credit cards, keys, books and records, customer and
         supplier lists, and financial and other information relating to the
         business of the Company and its prospective acquisition candidates. The
         Company understands and accepts that you have and plan to keep certain
         industry journals and directories, trade show handouts, promotional
         mailings and videos and other similar materials.

4.       In consideration of the payments set forth above, you hereby, on behalf
         of yourself, your executors, heirs, administrators, assigns, and anyone
         else claiming by, through or under you, release and forever discharge
         the Company, its subsidiaries, affiliates, predecessors, successors,
         assigns, partners, agents, employees, officers, and directors
         (collectively the Company) of, from and with respect to any and all
         claims, demands, and liabilities whatsoever, in law or in equity,
         existing up to the date hereof, including, but not limited to, any
         claims arising out of, based on or connected with the dealings between
         the parties, your employment by the Company, and the termination of
         that employment, including, but not limited to, any causes of action or
         claims for unlawful employment discrimination arising under or based on
         Title VII of the Civil Rights Act

<PAGE>   2

Mr. Thomas E. Gildershleeve
February 16, 2000
Page 2

         of 1964, as amended, Massachusetts General Laws, Chapter 151B, and any
         other state or federal law, statute, order, public policy, regulation,
         or common law claim affecting or relating to the claims or rights of
         employees, which you had, now have, or claim to have against the
         Company, whether or not now known or anticipated; provided that you are
         not releasing (1) any claim you may have with respect to fraud or (2)
         any claims or rights you may have arising out of this Agreement.

5.       In exchange for the mutual promises and releases contained in this
         Agreement, the Company (as defined in paragraph 4 above) hereby
         releases and forever discharges you, your executors, heirs,
         administrators, partners and assigns of, from and with respect to any
         and all claims, demands, and liabilities whatsoever, in law or in
         equity, existing up to the date hereof, which it had, now has or claims
         to have against you, whether or not now known or anticipated; provided
         that the Company is not releasing (1) any claim it may have with
         respect to fraud or (2) its rights to enforce this Agreement.

6.       Each party hereby covenants and agrees that it will not directly or
         indirectly, and will not authorize or permit any third party acting on
         his or its behalf to, institute any investigation, claim or proceeding
         before any court, administrative or governmental body with regard to
         the subject matter of this Agreement or any of the matters for which
         such party has released the other party as provided above; provided,
         however, that nothing herein shall prevent any party from enforcing any
         other rights or claims not expressly released as set forth in this
         Agreement.

7.       This Agreement contains the entire agreement between you and the
         Company and supercedes, cancels and terminates all other agreements
         between you and the Company, including, but not limited to, the
         proposed, and not executed, Change of Control Severance Agreement
         between the Company and you to be dated as of April 1, 1999. This
         Agreement may not be changed orally, but only by written agreement
         signed by you and a duly authorized officer of the Company. In the
         event this Agreement is not finally consummated, it and any preceding
         settlement discussions shall be without prejudice to any party, and
         shall not be used in any subsequent proceedings, judicial,
         administrative, or otherwise. This Agreement shall be governed by
         Massachusetts law.

<PAGE>   3

Mr. Thomas E. Gildershleeve
February 16, 2000
Page 3

Would you please sign and return the enclosed copy of this letter, thereby
confirming your agreement to the matters set forth herein.

On behalf of the Company, I want to wish you much success in your future
ventures.

                                               Very truly yours,

                                               NATIONAL DENTEX CORPORATION

                                               By:  /s/ David L. Brown
                                                    ---------------------------
                                                    David L. Brown, President
Received and agreed to:

/s/ Thomas E. Gildersleeve
------------------------------
Thomas E. Gildersleeve

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