Document:

<PAGE>

                                                                   EXHIBIT 10.20

                                AMENDMENT #6 TO
                             CONSULTING AGREEMENT

     This Amendment #6 to Consulting Agreement, dated as of September 14, 2000,
hereby amends the terms of that certain Consulting Agreement dated November 17,
1995, as amended, (hereinafter "Consulting Agreement") by and between Parametric
Technology Corporation, a Massachusetts corporation, having its principal
business address at 128 Technology Drive, Waltham, Massachusetts 02453
(hereinafter "PTC") and Michael E. Porter, an individual currently residing at
44 Green Hill Road, Brookline, Massachusetts 02146 (hereinafter "Consultant").

Article 3  Services To Be Performed By Consultant, is hereby amended by adding
the following Section 3.6:

   3.6  Consultant is engaged pursuant to this Amendment #6 to Consulting
   Agreement, to participate in two (2) top management seminars, including Chief
   Information Officer (CIO) seminars, consistent with the purposes and scope
   which Consultant was previously engaged to provide under Article 3 of the
   Consulting Agreement.

Article 4 Compensation And Expenses, is hereby amended by adding the following
Section 4.7:

   4.7  Option grant for services to be performed under Section 3.6.  In
   connection with those services to be performed pursuant to this Amendment #6
   to Consulting Agreement (as described in Section 3.6 above), Consultant shall
   receive an option to purchase 20,000 shares of PTC's common stock, $.01 par
   value per share, under the terms of the Stock Option Agreement dated
   September 14, 2000 between PTC and the Consultant attached hereto.

   IN WITNESS WHEREOF, the parties have executed this Amendment #6 to Consulting
Agreement as of the date and year first above written.

Consultant                       Parametric Technology Corporation

/s/ Michael E. Porter              /s/ C. Richard Harrison
-----------------------------      ---------------------------------------
Michael E. Porter                  C. Richard Harrison
                                   President and Chief Executive Officer
<PAGE>

No. 038504                                                       20,000 Shares

                       PARAMETRIC TECHNOLOGY CORPORATION
                       1997 Incentive Stock Option Plan

                     Nonstatutory Stock Option Certificate

                              September 14, 2000

     Parametric Technology Corporation (the "Company"), a Massachusetts
corporation, hereby grants to the person named below an option to purchase
shares of Common Stock, $0.01 par value, of the Company (the "Option") under and
subject to the Company's 1997 Incentive Stock Option Plan (the "Plan")
exercisable on the following terms and conditions set forth below and those
attached hereto and in the Plan:

Name of Optionholder:             Michael E. Porter

Social Security Number            ###-##-####

Number of Shares:                 20,000

Option Price:                     $ 13.1875

Date of Grant:                    September 14, 2000

Expiration:                       September 14, 2005

Exercisability Schedule:

        on or after September 14, 2000, as to 50% of the shares,
        on or after October 1, 2000, as to 50% of the shares,

   provided that Optionholder's consulting agreement with the Company is not
   terminated earlier, in which event the Option, (i) to the extent exercisable
   at the date of such termination, may not be exercised as to any shares after
   the expiration of seven (7) months from the date of such termination, and
   (ii) to the extent not exercisable at the date of such termination, shall be
   canceled as to any such shares effective on the date of such termination.

     This Option shall not be treated as an Incentive Stock Option under section
422 of the Internal Revenue Code of 1986, as amended.

     By acceptance of this Option, the Optionholder agrees to the terms and
conditions set forth above and those attached hereto and in the Plan.

OPTIONHOLDER                       PARAMETRIC TECHNOLOGY CORPORATION

By: /s/ Michael E. Porter          By: /s/ Edwin J. Gillis
    ---------------------------    -----------------------------------
    Optionholder                   Executive Vice President - CFO
<PAGE>

       PARAMETRIC TECHNOLOGY CORPORATION 1997 INCENTIVE STOCK OPTION PLAN

                 Nonstatutory Stock Option Terms And Conditions

     1.   Plan Incorporated by Reference.  This Option is issued pursuant to the
          ------------------------------
terms of the Plan and may be amended as provided in the Plan. Capitalized terms
used and not otherwise defined in this certificate have the meanings given to
them in the Plan.  This certificate does not set forth all of the terms and
conditions of the Plan, which are incorporated herein by reference.  The
Committee administers the Plan and its determinations regarding the operation of
the Plan are final and binding.  Copies of the Plan may be obtained upon written
request without charge from the Corporate Counsel of the Company.

     2.   Option Price.  The price to be paid for each share of Common Stock
          ------------
issued upon exercise of the whole or any part of this Option is the Option Price
set forth on the face of this certificate.

     3.   Exercisability Schedule.  This Option may be exercised at any time and
          -----------------------
from time to time for the number of shares and in accordance with the
exercisability schedule set forth on the face of this certificate, but only for
the purchase of whole shares.  This Option may not be exercised as to any shares
after the Expiration Date.

     4.   Method of Exercise.  To exercise this Option, the Optionholder shall
          ------------------
deliver written notice of exercise to the Company specifying the number of
shares with respect to which the Option is being exercised accompanied by
payment of the Option Price for such shares in cash, by certified check or in
such other form, including shares of Common Stock of the Company valued at their
Fair Market Value on the date of delivery or a payment commitment of a financial
or brokerage institution, as the Committee may approve. Promptly following such
notice, the Company will deliver to the Optionholder a certificate representing
the number of shares with respect to which the Option is being exercised.

     5.   No Right To Employment. No person shall have any claim or right to be
          ----------------------
granted an Option.  Each employee of the Company or any of its Affiliates is an
employee-at-will (that is to say that either the Participant or the Company or
any Affiliate may terminate the employment relationship at any time for any
reason or no reason at all) unless, and only to the extent, provided in a
written employment agreement for a specified term executed by the chief
executive officer of the Company or his duly authorized designee or the
authorized signatory of any Affiliate.  Neither the adoption, maintenance, nor
operation of the Plan nor any Option hereunder shall confer upon any employee of
the Company or of any Affiliate any right with respect to the continuance of
his/her employment by the Company or any such Affiliate nor shall they interfere
with the right of the Company (or Affiliate) to terminate any employee at any
time or otherwise change the terms of employment, including, without limitation,
the right to promote, demote or otherwise re-assign any employee from one
position to another within the Company or any Affiliate.

     6.   Effect of Grant.  Participant shall not earn any Options granted
          ----------------
hereunder until such time as all the conditions put forth herein and in the Plan
which are required to be met in order to exercise the Option have been fully
satisfied.

     7.   Recapitalization, Mergers, Etc.  As provided in the Plan, in the
          ------------------------------
event of corporate transactions affecting the Company's outstanding Common
Stock, the number and kind of shares subject to this Option and the exercise
price hereunder shall be equitably adjusted. If such transaction involves a
consolidation or merger of the Company with another entity, the sale or exchange
of all or substantially all of the assets of the Company or a reorganization or
liquidation of the Company, then in lieu of the foregoing, the Committee may
upon written notice to the Optionholder provide that this Option shall terminate
on a date not less than 20 days after the date of such notice unless theretofore
exercised. In connection with such notice, the Committee may in its discretion
accelerate or waive any deferred exercise period.

     8.   Option Not Transferable.  This Option is not transferable by the
          -----------------------
Optionholder otherwise than by will or the laws of descent and distribution, and
is exercisable, during the Optionholder's lifetime, only by the Optionholder.
The naming of a Designated Beneficiary does not constitute a transfer.
<PAGE>

     9.   Termination of Employment or Engagement.  If the Optionholder's status
          ----------------------------------------
as an employee or consultant of (a) the Company, (b) an Affiliate, or (c) a
corporation (or parent or subsidiary corporation of such corporation) issuing or
assuming a stock option in a transaction to which section 424(a) of the Code
applies, is terminated for any reason (voluntary or involuntary) and the period
of exercisability for a particular Option following such termination has not
been specified by the Board, each such Option then held by that Participant
shall expire to the extent not previously exercised ten (10) calendar days after
such Participant's employment or engagement is terminated, except that -
                                                           ------ ----

  (a)     If the Participant is on military, sick leave or other bona fide leave
                                                                 ---- ----
of absence (such as temporary employment by the federal government), his or her
employment or engagement with the Company will be treated as continuing intact
if the period of such leave does not exceed ninety (90) days, or, if longer, so
long as the Participant's right to reemployment or the survival of his or her
service arrangement with the Company is guaranteed either by statute or by
contract; otherwise, the Participant's employment or engagement will be deemed
to have terminated on the 91st day of such leave.

  (b)     If the Participant's employment is terminated by reason of his or her
retirement from the Company at normal retirement age, each Option then held by
the Participant, to the extent exercisable at retirement, may be exercised by
the Participant at any time within three (3) months after such retirement unless
terminated earlier by its terms.

  (c)     If the Participant's employment or engagement is terminated by reason
of his or her death, each Option then held by the Participant, to the extent
exercisable at the date of death, may be exercised at any time within one year
after that date (unless terminated earlier by its terms) by the person(s) to
whom the Participant's option rights pass by will or by the applicable laws of
descent and distribution.

  (d)     If the Participant's employment or engagement is terminated by reason
of his or her becoming permanently and totally disabled, each Option then held
by the Participant, to the extent exercisable upon the occurrence of permanent
and total disability, may be exercised by the Participant at any time within one
(1) year after such occurrence unless terminated earlier by its terms. For
purposes hereof, an individual shall be deemed to be "permanently and totally
disabled" if he or she is unable to engage in any substantial gainful activity
by reason of any medically determinable physical or mental impairment which can
be expected to result in death or which has lasted or can be expected to last
for a continuous period of not less than twelve (12) months. Any determination
of permanent and total disability shall be made in good faith by the Company on
the basis of a report signed by a qualified physician.

     10.  Compliance with Securities Laws.  It shall be a condition to the
          -------------------------------
Optionholder's right to purchase shares of Common Stock hereunder that the
Company may, in its discretion, require (a) that the shares of Common Stock
reserved for issuance upon the exercise of this Option shall have been duly
listed, upon official notice of issuance, upon any national securities exchange
or automated quotation system on which the Company's Common Stock may then be
listed or quoted, (b) that either (i) a registration statement under the
Securities Act of 1933 with respect to the shares shall be in effect, or (ii) in
the opinion of counsel for the Company, the proposed purchase shall be exempt
from registration under that Act and the Optionholder shall have made such
undertakings and agreements with the Company as the Company may reasonably
require, and (c) that such other steps, if any, as counsel for the Company shall
consider necessary to comply with any law applicable to the issue of such shares
by the Company shall have been taken by the Company or the Optionholder, or
both.  The certificates representing the shares purchased under this Option may
contain such legends as counsel for the Company shall consider necessary to
comply with any applicable law.

     11.  Payment of Taxes.  The Optionholder shall pay to the Company, or make
          ----------------
provision satisfactory to the Company for payment of, any taxes required by law
to be withheld with respect to the exercise of this Option.  The Committee may,
in its discretion, require any other Federal or state taxes imposed on the sale
of the shares to be paid by the Optionholder. In the Committee's discretion,
such tax obligations may be paid in whole or in part in shares of Common Stock,
including shares retained from the exercise of this Option, valued at their Fair
Market Value on the date of delivery.  The Company and its Affiliates may, to
the extent permitted by law, deduct any such tax obligations from any payment of
any kind otherwise due to the Optionholder.

     Adopted November 14, 1996<PAGE>

                                                                   EXHIBIT 10.21

                                    PROPERTY

                             I N D E X T O L E A S E
                             -----------------------

                                      FROM
                                      ----

                      BOSTON PROPERTIES LIMITED PARTNERSHIP

                                       TO
                                       --
                        PARAMETRIC TECHNOLOGY CORPORATION

ARTICLE
NUMBER                 CAPTION                                          PAGE
------                 -------                                          ----

  I           BASIC LEASE PROVISIONS AND
              ENUMERATION OF EXHIBITS                                    1

              Section 1.1    Introduction                                1
              Section 1.2    Background                                  1
              Section 1.3    Basic Data                                  2
              Section 1.4    Enumeration of Exhibits                     4

  II          PREMISES                                                   5

              Section 2.1    Demise and Lease of Premises                5

  III         LEASE TERM AND EXTENSION OPTIONS                           6

              Section 3.1    Term                                        6
              Section 3.2    Extension Options                           6

  IV          CONSTRUCTION                                               8

              Section 4.0    Landlord's Base Building Work               8
              Section 4.1    Cost of Landlord's Work                    11
              Section 4.2    Changes in Landlord's Work                 12
              Section 4.3    Work performed by Tenant                   12
              Section 4.4    Quality and Performance of Work            13
              Section 4.5    Early Access                               13
              Section 4.6    Unused Construction Contingency            13

   V          ANNUAL FIXED RENT                                         14

                                      -i-
<PAGE>

              Section 5.1    Fixed Rent                                     14

      VI      TAXES AND OPERATING EXPENSES                                  15

              Section 6.1    Definitions                                    15
              Section 6.2    Operating Costs Defined                        17
              Section 6.3    Tenant's Payments of Operating Expenses        21
              Section 6.4    Effect of Multiple Rent Commencement Dates     23
              Section 6.5    Management Fee Rent                            23

      VII     LANDLORD'S REPAIRS AND SERVICES                               24

              Section 7.1    Structural Repairs                             24
              Section 7.2    Other Repairs to be Made By Landlord           24
              Section 7.3    Services to be Provided by Landlord            24
              Section 7.4    Electricity                                    25
              Section 7.5    No Damage                                      25

     VIII     TENANT'S REPAIRS                                              26

              Section 8.1    Tenant's Repairs and Maintenance               26

      IX      ALTERATIONS                                                   27

              Section 9.1    Landlord's Approval                            27
              Section 9.1.1  Certain Alterations                            28
              Section 9.2    Conformity of Work                             28
              Section 9.3    Performance of Work, Governmental
                             Permits and Insurance                          28
              Section 9.4    Liens                                          29
              Section 9.5    Nature of Alterations                          29

       X      INTENTIONALLY OMITTED                                         30

      XI      CERTAIN TENANT COVENANTS                                      30

      XII     ASSIGNMENT AND SUBLETTING                                     33

              Section 12.1  Restrictions on Transfer                        33
              Section 12.2  Exceptions for Parent or Subsidiary             33
              Section 12.3  Exceptions for Certain Subleases                35
              Section 12.4  Consent of Landlord                             35
              Section 12.5  Tenant's Notice                                 36
              Section 12.6  Profit on Subleasing, Assignment, and

                                     -ii-
<PAGE>

<TABLE>
<S> <C>     <C>                                                                <C>
                            Certain Telecommunications License                    36
              Section 12.7  Additional Conditions                                 37

     XIII     INDEMNITY AND COMMERCIAL GENERAL
              LIABILITY INSURANCE                                                 38

              Section 13.1  Tenant's Indemnity                                    38
              Section 13.1.1   Landlord's Indemnity                               39
              Section 13.2  Commercial General Liability Insurance                40
              Section 13.3  Tenant's Property Insurance                           40
              Section 13.4  Non-Subrogation                                       41
              Section 13.5  Tenant's Risk                                         41
              Section 13.6  Landlord's Insurance                                  41

      XIV     FIRE, CASUALTY AND TAKING                                           42

              Section 14.1  Repair of Damage Caused by Casualty                   42
              Section 14.2  Landlord's Termination Rights                         43
              Section 14.3  Tenant's Termination Rights                           45
              Section 14.4  General Provisions Relating to
                            Any Casualty Termination                              47
              Section 14.5  Intentionally Omitted                                 47
              Section 14.6  Tenant's Termination Rights
                            Based upon Taking                                     48
              Section 14.7  General Taking Provisions                             48
              Section 14.8  Taking Proceeds                                       49
              Section 14.9  Temporary Taking                                      50

      XV      DEFAULT                                                             50

              Section 15.1  Tenant's Default                                      50
              Section 15.2  Termination; Re-Entry                                 51
              Section 15.3  Continued Liability; Re-Letting                       51
              Section 15.4  Liquidated Damages                                    52
              Section 15.5  Intentionally Omitted                                 53
              Section 15.6  Landlord's Default; Tenant's Self-Help                54

      XVI     MISCELLANEOUS PROVISIONS                                            56

              Section 16.1  Waiver                                                56
              Section 16.2  Cumulative Remedies                                   56
              Section 16.3  Quiet Enjoyment                                       56
              Section 16.4  Surrender                                             57
              Section 16.5  Brokerage                                             58
              Section 16.6  Invalidity of Particular Provisions                   58
</TABLE>

                                     -iii-
<PAGE>

<TABLE>
<S>         <C>               <C>                                             <C>
              Section 16.7      Provisions Binding, Etc.                          58
              Section 16.8      Recording                                         59
              Section 16.9      Notices and Time for Action                       59
              Section 16.10     When Lease Becomes Binding                        60
              Section 16.11     Paragraph Headings                                60
              Section 16.12     Rights of Mortgagee                               60
              Section 16.13     Intentionally Omitted                             61
              Section 16.14     Intentionally Omitted                             61
              Section 16.15     Landlord's Financing, Tenant's
                                Shadow Rating                                     61
              Section 16.16     Status Report and Financial Statements            61
              Section 16.17     Intentionally Omitted                             62
              Section 16.18     Holding Over                                      62
              Section 16.19     Entry by Landlord                                 62
              Section 16.20     Tenant's Payments                                 63
              Section 16.21     Late Payment                                      63
              Section 16.22     Counterparts                                      63
              Section 16.23     Entire Agreement                                  63
              Section 16.24     Limitations on Landlord                           64
              Section 16.25     No Partnership                                    64
              Section 16.26     Letters of Credit                                 64
              Section 16.27     Governing Law                                     67
              Section 16.28     Signage                                           67
              Section 16.29     Intentionally Omitted                             68
              Section 16.30     Landlord's Consent                                68
              Section 16.31     Tenant's Right of First Refusal to
                                Purchase the Property                             68
              Section 16.32     Arbitration                                       72
              Section 16.33     Confidentially                                    73

         Exhibit A-1       Legal Description

         Exhibit A-2       Site Plan

         Exhibit B-1       Base Building Work Plans and Specifications

         Exhibit B-2       Tenant Improvement Work Plans and Specifications

         Exhibit B-3       Plans and Specifications for Off-Site Mitigation Work

         Exhibit B-4       Qualifications and Assumptions with respect to Landlord's Work

         Exhibit C         Landlord's Services

         Exhibit D         Property Floor Plans
</TABLE>

                                     -iv-
<PAGE>

         Exhibit E         Form of Commencement Date Agreement

         Exhibit F         Intentionally Omitted

         Exhibit G         Broker Determination of Prevailing Fair Market Rent

         Exhibit H-1       Form of General Letter of Credit

         Exhibit H-2       Form of TI Letter of Credit

                                      -v-
<PAGE>

                  140 KENDRICK STREET, NEEDHAM, MASSACHUSETTS

     THIS INSTRUMENT IS AN INDENTURE OF LEASE made as of this 14th day of
December, 1999 ("Execution Date") in which the Landlord and the Tenant are the
parties hereinafter named, and which relates to the land ("Land") and the
buildings to be constructed thereon, now know as and numbered 140 Kendrick
Street, Needham, Massachusetts.

     The parties to this instrument hereby agree with each other as follows:

                                   ARTICLE I
                                   ---------
              BASIC LEASE PROVISIONS AND ENUMERATIONS OF EXHIBITS
              ---------------------------------------------------

1.1  INTRODUCTION.  The following sets forth the basic data and identifying
     ------------
     Exhibits elsewhere hereinafter referred to in this Lease, and, where
     appropriate, constitute definitions of the terms hereinafter listed.

1.2  BACKGROUND.   Reference is made to the following:
     ----------

     A.   Prior to the Execution Date, Tenant owned the Land. A legal
description of the Land is attached hereto as Exhibit A-1 and is substantially
as shown in the site plan ("Site Plan") attached hereto as Exhibit A-2.

     B.   Tenant conveyed the Land to Landlord on the Execution Date pursuant to
a Purchase and Sale and Leaseback Agreement dated December 10, 1999 by and
between Tenant, as Seller, and Landlord, as Buyer.

     C.   The parties intend that Landlord construct three buildings, including
a concourse between two of the buildings, a 1,127 space parking structure
("Garage"), and 207 surface parking spaces on the Land. Each building is
referred to herein as a "Building", and the Buildings are collectively referred
to herein as the "Buildings". The three buildings are referred to herein as
Building A, Building B, and Building C and are shown on the Site Plan.
"Landlord's Work" shall be defined as base building work ("Base Building Work")
described in the plans and specifications referenced on Exhibit B-1, the tenant
improvement work ("Tenant Improvement Work") described in the plans and
specifications referenced on Exhibit B-2, the off-site mitigation work described
on Exhibit B-3, and the Qualifications and Assumptions with respect to
Landlord's Work set forth on Exhibit B-4.

1.3  BASIC DATA.
     ----------

                                      -1-
<PAGE>

     Execution Date:                      December 14, 1999

     Landlord:                            Boston Properties Limited Partnership

     Present Mailing Address
     of Landlord:                         800 Boylston Street
                                          Boston, Massachusetts 02199-8001
                                          Attention: General Counsel

     Landlord's Construction
     Representative:                      James C. Rosenfeld or John Camera

     Tenant:                              Parametric Technology Corporation,
                                          a Massachusetts corporation

     Present Mailing Address of Tenant:   128 Technology Drive
                                          Waltham, Massachusetts 02453
                                          Attention: Mr. Joseph M. Joyce,
                                                     Director of Real Estate

     Tenant's Construction
     Representative:                      Mr. Joseph M. Joyce

     Term or Lease Term:                  Commencing on the Commencement Date
                                          and terminating as of the date
                                          ("Expiration Date") twelve (12) years
                                          after the first Rent Commencement
                                          Date.

     Extension Options:                   Three (3) consecutive periods of five
                                          (5) years each as provided in and on
                                          the terms set forth in Section 3.2
                                          hereof.

     Rent Year:                           If the Rent Commencement Date in
                                          respect of each of Building A,
                                          Building B, and Building C occurs on
                                          or before March 1, 2001, then:

                                          (i) the first Rent Year in respect of
                                          each Building shall commence as of the
                                          Rent Commencement Date in respect of
                                          such Building and the first Rent Year
                                          in respect of all three Buildings
                                          shall end as of the day immediately
                                          preceding the first anniversary of the
                                          first Rent Commencement Date, and

                                      -2-
<PAGE>

                                          (ii) each subsequent Rent Year for all
                                          three Buildings shall be the twelve
                                          month period commencing as of any
                                          anniversary of the first Rent
                                          Commencement Date.

                                          If the Rent Commencement Date in
                                          respect of any Building occurs after
                                          March 1, 2001, then the Rent Year in
                                          respect of each Building shall be
                                          defined as the twelve (12) month
                                          period commencing as of the Rent
                                          Commencement Date in respect of such
                                          Building, or as of any anniversary of
                                          such Rent Commencement Date.

     Commencement Date:                   The Execution Date.

     Rent Commencement Date:              See Section 3.1.

     Premises or Property:                The Land and all of the improvements
                                          thereon to be constructed as part of
                                          Landlord's Work ("Improvements").

     Rentable Floor Area of
     the Buildings:                       Is agreed to be 380,987 square feet.
                                          The Rentable Floor Area of Buildings
                                          is as follows:

                                          Building          Rentable Floor Area

                                             A              108,907 square feet
                                             B              101,346 square feet
                                             C              170,734 square feet

     Annual Fixed Rent:
          Initial Term:

         Rent         Annual Fixed Rent            Monthly Payment
                                  -----                    -------
         Year

          1-4           $8,659,834.51                $721,652.88
          5-8           $9,376,090.07                $781,340.84
         9-12          $10,092,345.63                $841,028.80

                  Extension Options:                 See Section 3.2.

                                      -3-
<PAGE>

     Tenant Electricity:                  Separately metered to Tenant as
                                          described in Section 7.4.

     Additional Rent:                     All charges and other sums payable by
                                          Tenant as set forth in this Lease, in
                                          addition to Annual Fixed Rent.

     Management Fee:                      See Section 6.5.

     Initial Minimum Limits               $10,000,000 combined (primary and
     of Tenant's Commercial               excess coverage) single limit per
     General Liability Insurance:         occurrence on a per location basis.

     Permitted Use:                       General office use, research and
                                          development, and other ancillary uses
                                          (including a cafeteria), subject to
                                          applicable zoning and other laws and
                                          all governmental permits and approvals
                                          applicable to the Property.

     Broker:                              Spaulding & Slye Colliers Services
                                          Limited Partnership

     Letters of Credit:
       TI Letter of Credit:               $16,429,000.00
       General Letter of Credit:          $8,700,000.00, subject to reduction in
                                          accordance with Section 16.26 of the
                                          Lease, and subject to increase in
                                          accordance with Section 12.2.

     Landlord's Work:                     See Paragraph C of Section 1.2.

     Base Building Work:                  See Paragraph C of Section 1.2.

     Tenant Improvement Work:             See Paragraph C of Section 1.2.

     Off-Site Mitigation Work:            See Paragraph C of Section 1.2.

1.4  ENUMERATION OF EXHIBITS. The following Exhibits attached hereto are a
     -----------------------
     part of this Lease, are incorporated herein by reference, and are to be
     treated as a part of this Lease for all purposes. Undertakings contained in
     such Exhibits are agreements on the part of Landlord and Tenant, as the
     case may be, to perform the obligations stated therein to be performed by
     Landlord and Tenant, as and where stipulated therein.

                                      -4-
<PAGE>

         Exhibit A-1       Legal Description of Land

         Exhibit A-2       Site Plan

         Exhibit B-1       Plans and Specifications for Base Building Work

         Exhibit B-2       Plans and Specifications for Tenant Improvement Work

         Exhibit B-3       Off-Site Mitigation Work

         Exhibit B-4       Assumptions and Qualifications with respect to
                           Landlord's Work

         Exhibit C         Landlord's Services

         Exhibit D         Intentionally Omitted

         Exhibit E         Form of Commencement Date Agreement

         Exhibit F         Intentionally omitted.

         Exhibit G         Broker Determination of Prevailing Fair Market Rent

         Exhibit H-1       Form of General Letter of Credit

         Exhibit H-2       Form of TI Letter of Credit

                                  ARTICLE II
                                  ----------
                                   PREMISES
                                   --------
2.1      DEMISE AND LEASE OF PREMISES.
         ----------------------------

         A.  Landlord hereby demises and leases to Tenant, and Tenant hereby
         hires and accepts from Landlord, the entire Premises, subject to
         provisions of this Lease.

         B.  Measurement of Rentable Floor Area. The parties acknowledge and
         agree that: (i) they have agreed upon the Rentable Floor Area of the
         Buildings, (ii) the agreed upon amounts are based upon the plans and
         specifications for the Base Building Work, as described on Exhibit B-1,
         which were prepared by the Tenant and which were approved by Landlord,
         and (iii) such agreed upon amounts are set forth in Section 1.3 of this
         Lease.

                                  ARTICLE III
                                  -----------

                                      -5-
<PAGE>

                        LEASE TERM AND EXTENSION OPTIONS
                        --------------------------------

3.1  TERM.  The Term of this Lease shall be the period specified in Section 1.3
     ----
     hereof as the "Lease Term", unless sooner terminated or extended as herein
     provided.  The Lease Term hereof shall commence on the Execution Date.  The
     Rent Commencement Date in respect of each Building shall be defined as the
     first to occur of:

     A.   The Substantial Completion Date, as defined in Section 4.0, with
          respect to such Building; or

     B.   With Landlord's prior written approval, which approval shall not be
          unreasonably withheld, the date on which Tenant commences use of such
          Building, or any portion of such Building, for the regular conduct of
          Tenant's business (the parties hereby agreeing that the installation
          and testing of Tenant's furniture, fixtures and equipment shall not be
          considered to be business purposes).

     At the request of either Landlord or Tenant and as soon as may be
     convenient after each Rent Commencement Date has been determined, Landlord
     and Tenant agree to join with each other in the execution, in the form of
     Exhibit E hereto, of a written Commencement Date Agreement in which such
     Rent Commencement Date and specified Lease Term of this Lease shall be
     stated, provided however, that the failure by either party to execute such
     Commencement Date Agreements shall not affect the Rent Commencement Dates
     or the Lease Term.

3.2  EXTENSION OPTIONS.
     -----------------

     A.   Exercise of Options. On the conditions (which conditions Landlord
          -------------------
     may waive by written notice to Tenant) that: (i) at the time of exercise of
     the herein described options to extend there exists no "Event of Default"
     (defined in Section 15.1) and that this Lease is still in full force and
     effect, and (ii) Tenant is in compliance with the Occupancy Condition, as
     hereinafter defined, as of the commencement of the Extended Term in
     question, Tenant shall have the right to extend the Term hereof for three
     (3) consecutive periods of five (5) years each as hereinafter set forth.
     Each option period is sometimes herein referred to as the "Extended Term."
     Each Extended Term shall be upon all the same terms, conditions, covenants
     and agreements herein which were in effect immediately preceding the
     commencement of such Extended Term, except that: (i) the Annual Fixed Rent
     for each Extended Term shall be equal to ninety-five percent (95%) of the
     Prevailing Fair Market Rent as defined in Exhibit G and as determined in
     accordance with Paragraph B of this Section 3.2, and (ii) there shall be no
     further option to extend the Term other than the three (3) five (5) year
     Extended Terms provided in this Section 3.2.

                                      -6-
<PAGE>

     B.  Determination of Prevailing Fair Market Rent and Exercise of Extension
         ----------------------------------------------------------------------
     Option.  If Tenant desires to exercise its first option to extend the Term,
     ------
     then Tenant shall give a written request ("Tenant's Request") to Landlord
     not earlier than thirty (30) months nor later than twenty-six (26) months
     prior to the expiration of the initial Term of this Lease requesting
     Landlord's quotation to Tenant of a proposed Annual Fixed Rent for the
     applicable Extended Term. If Tenant desires to exercise either its second
     or third option to extend the Term, then Tenant shall give Tenant's Request
     to Landlord not earlier than twenty-four (24) months nor later than twenty
     (20) months prior to the expiration of the first Extended Term or the
     second Extended Term, as the case may be. Landlord shall, within ten (10)
     days of Landlord's receipt of any such Tenant's Request, give to Tenant a
     written notice ("Landlord's Quotation") setting forth Landlord's quotation
     of such Annual Fixed Rent. If, at the expiration of the thirty (30) day
     period (the "Negotiation Period") after the date Tenant receives Landlord's
     Quotation, Landlord and Tenant have not reached agreement on a
     determination of an Annual Fixed Rent for such Extended Term and executed a
     written instrument extending the Term of this Lease pursuant to such
     agreement, then Tenant shall have the right, for thirty (30) days following
     the expiration of the Negotiation Period, to give written notice ("Tenant's
     Exercise Notice") exercising Tenant's right to extend the term of the Lease
     for the Extended Term in question. Tenant's Exercise Notice may require
     that the determination of the Annual Fixed Rent to be paid by Tenant during
     the Extended Term in question be submitted to a broker determination (the
     "Broker Determination") of the Prevailing Fair Market Rent (as defined in
     Exhibit G) for such Extended Term in the manner set forth in Exhibit G. If
     Tenant fails timely to give Tenant's Request, or if Tenant fails timely to
     give Tenant's Exercise Notice, then Tenant shall have no further right to
     extend the term of this Lease, time being of the essence of this Section
     3.2. If Tenant timely gives Tenant's Request and Tenant's Exercise Notice,
     but Tenant does not require a Broker Determination, then the Annual Fixed
     Rent payable by Tenant for the Extended Term in question shall be equal to
     the Annual Fixed Rent set forth in Landlord's Quotation. If Tenant timely
     gives Tenant's Request and Tenant's Exercise Notice, and if Tenant's
     exercise notice requires a Broker Determination, then the Annual Fixed Rent
     for such Extended Term shall be based upon ninety-five (95%) percent of the
     Prevailing Fair Market Rent of the Premises as of the commencement of such
     Extended Term, as determined by the Broker Determination.

     C.  Upon the timely giving of Tenant's Request and of Tenant's Exercise
     Notice by Tenant with respect to any Extended Term, in accordance with the
     provisions of Section 3.2(B) above, then this Lease and the Lease Term
     hereof shall automatically be deemed extended, for the applicable Extended
     Term, without the necessity for the execution of any additional documents,
     except that Landlord and Tenant agree to enter into an instrument in
     writing setting forth the Annual Fixed Rent for the applicable Extended
     Term as determined in the relevant manner set forth in this Section 3.2;
     and in such event all references

                                      -7-
<PAGE>

     herein to the Lease Term or the Term of this Lease shall be construed as
     referring to the Lease Term, as so extended, unless the context clearly
     otherwise requires. Notwithstanding anything contained herein to the
     contrary, in no event shall Tenant have the right to exercise more than one
     extension option at a time and, further, Tenant shall not have the right to
     exercise its second extension option unless it has duly exercised its first
     extension option and Tenant shall not have the right to exercise its third
     extension option unless it has duly exercised both its first and second
     extension options. In no event shall the Lease Term hereof be extended for
     more than fifteen (15) years after the expiration of the Original Lease
     Term hereof.

     D.   Occupancy Condition.  For the purposes of this Section 3.2, Tenant
          -------------------
     shall be deemed to have satisfied the "Occupancy Condition" if: (i) Tenant
     has not (except for an assignment permitted without Landlord's consent
     under Section 12.2) assigned its interest in the Lease, and (ii) any of one
     of the following conditions are satisfied:

          (x)  Tenant has not (except for subleases permitted without Landlord's
          consent under Section 12.2) subleased more than fifty-five (55%)
          percent of the Premises, or

          (y)  Tenant has not (except for subleases permitted without Landlord's
          consent under Section 12.2) subleased any portion of either Building A
          or of Building B; or

          (z)  Tenant has not (except for subleases permitted without Landlord's
          consent under Section 12.2) subleased any portion of Building C.

                                   ARTICLE IV
                                   ----------
                                  CONSTRUCTION
                                  ------------

4.0  LANDLORD'S WORK.
     ---------------

     A.   Target Dates.  Subject to delays due to Landlord's Force Majeure, as
     defined in Section 7.5, Landlord shall use reasonable speed and diligence
     in the performance of Landlord's Work, to achieve the Actual Substantial
     Completion Dates with respect to both Building A and Building B on or
     before December 15, 2000 and to achieve the Actual Substantial Completion
     Date with respect to all of Landlord's Work on or before January 25, 2001
     (said December 15, 2000 and January 25, 2001 dates being referred to herein
     as "Target Dates"). Landlord shall use all diligent efforts to enforce its
     rights against Landlord's general contractor to achieve the Actual
     Substantial Completion Date of Landlord's Work on or before the Target
     Dates; however, notwithstanding anything to the contrary herein contained,
     but subject to Paragraph F of this Section 4.0, Tenant shall have no claim
     against Landlord, and Landlord shall have no liability to

                                      -8-
<PAGE>

     Tenant, based upon Landlord's failure to substantially complete Landlord's
     Work on or before such Target Dates. Landlord shall, during the performance
     of Landlord's Work, furnish to Tenant monthly reports of the status of the
     Landlord's Work including a construction schedule and the completion of
     work to date.

     B.   The "Actual Substantial Completion Date" with respect to any Building
     shall be defined as the date on which: (i) the portion of Landlord's Work
     to be performed with respect to such Building is substantially complete,
     other than Punch List Items, as hereinafter defined, and (ii) subject to
     Paragraph G of this Section 4.0, Landlord has obtained a certificate of
     occupancy permitting Tenant to legally occupy such Building, and (iii) the
     portion of Landlord's Work to be performed with respect to the Garage is
     substantially complete, other than Punch List Items, and (iv) subject to
     Paragraph G of this Section 4.0, Landlord has obtained a certificate of
     occupancy ("Garage Certificate of Occupancy") permitting Tenant to legally
     use the Garage. Any dispute with respect to any Substantial Completion Date
     shall be submitted to arbitration in accordance with Section 16.32 of the
     Lease and the decision of the arbitrators as to such dates shall be deemed
     conclusive and binding on both Landlord and Tenant. Nothing contained in
     this paragraph shall limit or qualify or prejudice any other covenants,
     agreements, terms, provisions and conditions contained in this Lease.

     C.   The "Substantial Completion Date" with respect to any Building shall
     be the "Actual Substantial Completion Date" with respect to such Building,
     unless Landlord's Work is actually delayed by Tenant Delays, as hereinafter
     defined, in which event the "Substantial Completion Date" with respect to
     any Building shall be defined as the date that the Actual Substantial
     Completion Date with respect to such Building would have occurred but for
     such Tenant Delays.

     D.   "Punch List Items" shall be defined as minor, punch list type items of
     work and adjustment of equipment and fixtures in the Premises which can be
     completed after Tenant commences its occupancy of the Premises without
     causing material interference with Tenant's use of the Premises for the
     conduct of its business. Landlord shall complete, as soon as conditions
     practically permit, all Punch List Items, and Tenant shall cooperate with
     Landlord in providing access during the performance as may be required to
     complete such work in a normal manner. Notwithstanding the foregoing, after
     Tenant opens for business in the Premises, the completion of all Punch List
     Items which involve the making of noise which would interfere with the
     operation of a first-class business office or the creation of any dirt or
     debris in any portion of the Premises then occupied by Tenant will be
     performed after the Building's business hours. Landlord shall use all
     reasonable efforts to complete Punch List Items with respect to the portion
     of Landlord's Work performed for any Building within thirty (30) days after
     the Actual Substantial Completion Date for such Building, except Landlord
     shall use all reasonable efforts to complete Punch List Items which cannot
     reasonably

                                      -9-
<PAGE>

     be completed within thirty (30) days after such Actual Substantial
     Completion Date, as soon as reasonably possible after such Actual
     Substantial Completion Date.

     E.   A "Tenant Delay" shall be defined as any delay in the performance of
     Landlord's Work to the extent that such delay is directly caused by any
     act, omission, 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
     (including, without limitation, any such delay which results in a delay by
     Landlord in obtaining the Certificate of Occupancy).

     F.   Tenant's Termination Right.

          Notwithstanding anything to the contrary herein contained, if the
     first Rent Commencement Date does not occur on or before July 15, 2001,
     then Tenant shall have the right to terminate the Lease by giving Landlord
     a written notice ("Termination Notice") after July 15, 2001. If the first
     Rent Commencement Date does not occur on or before the date ninety (90)
     days after Landlord receives the Termination Notice from Tenant ("Effective
     Termination Date"), then the Term shall terminate effective as of the
     Effective Termination Date, Landlord shall promptly return both the General
     Letter of Credit and the TI Letter of Credit to Tenant, and neither party
     shall have any further liability to other party. If the Rent Commencement
     Date occurs on or before the Effective Termination Date, then the
     Termination Notice shall be void and without further force or effect and
     Tenant shall have no right to terminate the Lease pursuant to this
     Paragraph F.

     G.   Flammables Permit. Reference is made to the fact that, as of the
     Execution Date, a flammables permit or license ("Flammables Permit") has
     not been obtained from the Town of Needham ("Town") and that Landlord may
     not be able to obtain the Garage Certificate of Occupancy or the
     Certificate of Occupancy for any of the Buildings without obtaining the
     Flammables Permit. Landlord agrees, promptly after the Execution Date, to
     apply for, and to diligently pursue the obtaining of the Flammables Permit.
     Provided that Landlord has made such diligent efforts, as aforesaid, then
     the issuance of Certificates of Occupancy for the Garage or for any of the
     Buildings shall not be conditions to the occurrence of the Rent
                     ---
     Commencement Date for any of the Buildings if the sole reason why Landlord
     is unable to obtain any such Certificates of Occupancy is Landlord's
     inability to obtain the Flammables Permit. If the Town fails to issue the
     Flammables Permit before the portion of Landlord's Work to be performed
     with respect to the Garage or with respect to any Building is substantially
     complete, or if the Town denies the issuance of the Flammables Permit, or
     if the Town issues the Flammables Permit subject to conditions which are
     other than the filing of a complete and accurate application for the
     Flammables Permit and the payment of all application and license fees for
     the Flammables Permit, then, and

                                     -10-
<PAGE>

     in any of such circumstances: (i) it shall be deemed that the Flammables
     Permit has not been obtained, and (ii) Landlord shall diligently pursue all
     appeals which are available to Landlord to obtain the Flammables Permit as
     soon as possible. Landlord shall have no obligation to perform or be
     subject to any conditions imposed in connection with the issuance of the
     Flammables Permit.

4.1  COST OF LANDLORD'S WORK
     -----------------------

     A.  Subject to Paragraph C of this Section 4.1, Landlord shall be
     responsible for the entire cost of the Base Building Work.

     B.  Landlord shall fund the cost of Tenant Improvement Work, subject to the
     provisions of this Paragraph B.  Tenant shall pay to Landlord an amount
     ("Tenant Payment") equal to the sum of Sixteen Million Four Hundred Twenty-
     Thousand  ($16,429,000.00) Dollars towards the cost of performing the
     Tenant Improvement Work.  Tenant shall pay to Landlord the Tenant Payment
     as follows:

         .  Tenant shall pay to Landlord $4,699,000.00 on the Rent Commencement
            Date with respect to Building A
         .  Tenant shall pay to Landlord $4,370,000.00 on the Rent Commencement
            Date with respect to Building B
         .  Tenant shall pay to Landlord $7,360,000.00 on the Rent Commencement
            Date with respect to Building C.

     C.  Tenant shall be responsible for any costs incurred by Landlord in
     performing Landlord's Work to the extent that the same arise directly from
     Tenant Delays. Such costs, together with interest at the rate specified in
     Section 16.21, accruing on such costs from the date that such costs are
     incurred by Landlord until paid by Tenant, shall be due and payable by
     Tenant, as additional rent, after the final Rent Commencement Date within
     thirty (30) days of billing therefor.

     D.  As security for Tenant's obligation to pay the Tenant Payment to
     Landlord, Tenant shall, at the time that Tenant executes and delivers the
     Lease to Landlord, deliver to Landlord the TI Letter of Credit, as defined
     in Section 16.26. If Tenant fails timely to pay to Landlord any portion of
     the Tenant Payment when such portion is due, Landlord shall have the right,
     upon five (5) business days written notice to Tenant to draw down a portion
     of the TI Letter of Credit equal to the past due amount and to apply the
     proceeds of the TI Letter of Credit against such past due portion of the
     Tenant Payment. If for any reason any portion of the Tenant Payment is due
     and payable from Tenant on or after the date thirty (30) days prior to the
     Stated Expiration Date of the TI Letter of Credit (as the same may be
     extended), Tenant shall, within five (5) business days of demand by
     Landlord deliver to Landlord either an amendment of the TI Letter of Credit
     extending the Stated Expiration Date for an additional one (1) year period
     or a

                                     -11-
<PAGE>

     substitute TI Letter of Credit in place of the TI Letter of Credit for an
     additional one (1) year period. If Tenant fails timely to deliver such
     amendment or substitute TI Letter of Credit, Landlord shall have the right,
     without further notice, to draw down the entire TI Letter of Credit, less
     the amount of any portion of the Tenant Payment previously paid by Tenant
     to Landlord, and hold the proceeds of such draw in an interest bearing
     account as security for Tenant's obligation to pay the Tenant Payment, as
     aforesaid. Upon the full payment of the Tenant Payment to Landlord,
     Landlord shall return the TI Letter of Credit to Tenant.

4.2  CHANGES IN LANDLORD'S WORK.  Either party may initiate requests for changes
     --------------------------
     in the scope of Landlord's Work. Upon such a request, the parties shall
     work in good faith to negotiate the scope and effect of the proposed change
     and a new Lease to accommodate such proposed changes. However, in no event
     shall any changes be effected without the written consent of both Landlord
     and Tenant, and if a change which is proposed by either party is not agreed
     to in writing by both parties, then, notwithstanding anything to the
     contrary herein contained, neither party shall have any rights or
     liabilities to the other party based upon such proposed change and this
     Lease shall remain unchanged and in full force and effect.

4.3  WORK PERFORMED BY TENANT. Subject always to the provisions of this Lease,
     ------------------------
     when Tenant employs any contractors in preparing the Premises for Tenant's
     occupancy: (i) Landlord will give Tenant reasonable advance notice of the
     date on which 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, and (ii) 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. Subject to the foregoing clause (ii) of this
     Section 4.3, Landlord shall use reasonable efforts to accommodate the
     performance of the work to be performed by Tenant's contractors in
     preparing the Premises for Tenant's occupancy. Landlord's representatives
     shall meet with Tenant representatives periodically throughout the
     performance of Landlord's Work (at least monthly, and more frequently if
     reasonably requested by Tenant) to the end that Tenant shall have
     sufficient information about the schedule for the performance of Landlord's
     Work so that Tenant shall be able to schedule and coordinate the
     performance of any work or installations to be performed by Tenant with the
     performance of Landlord's Work.

4.4  QUALITY AND PERFORMANCE OF WORK.
     -------------------------------

     A.  All construction work required or permitted by this Lease shall, in all
     material respects, be done: (i) in accordance with the plans and
     specifications for Landlord's Work which are referenced on Exhibits B-1, B-
     2, B-3, and B-4, (ii) in

                                     -12-
<PAGE>

     a good and workmanlike manner, and (iii) in compliance with all applicable
     laws, ordinances, rules, regulations, statutes, by-laws, court decisions,
     and orders and requirements of all public authorities ("Legal
     Requirements") and all Insurance Requirements (as defined in Section 9.1
     hereof). Each party authorizes the other to rely in connection with design
     and construction upon the written approval or other written authorizations
     on the party's behalf by any Construction Representative of the party named
     in Section 1.3 or any person hereafter designated in substitution or
     addition by notice to the party relying.

     B.   Subject to the provisions of this Paragraph B, Landlord shall be
     responsible to Tenant for latent defects in Landlord's Work, but only: (i)
     to the extent that such latent defects are covered by valid and enforceable
     warranties which Landlord has from any contractor or vendor who provided
     labor and/or materials in connection with Landlord's Work, and (ii) to the
     extent that Tenant gives Landlord notice in writing of a defect in
     Landlord's Work within the applicable time period under any such warranty.
     As Landlord's sole obligation to Tenant based upon any such latent defect,
     Landlord shall, at Landlord's option, either pursue a claim for the
     correction of such defect directly against the contractor or vendor in
     question, or Landlord shall assign any such warranties to Tenant for
     enforcement.

4.5  EARLY ACCESS
     ------------

     With Landlord's prior written consent, which shall not be unreasonably
     withheld, conditioned or delayed, Tenant shall have the right, without
     payment of Annual Fixed Rent or other charges, to enter the Premises prior
     to the Substantial Completion Date, during normal business hours and such
     other times as Landlord's contractor is performing work on the Premises,
     and without payment of rent, to perform such work (including, without
     limitation, the installation of Tenant's computer room, furniture,
     equipment, and other personal property of Tenant) 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.

4.6  UNUSED CONSTRUCTION CONTINGENCY
     -------------------------------

     Reference is made to the fact that Landlord's general contractor is
     carrying a construction contingency in the amount of $1,250,000.00 under
     its Guaranteed Maximum Price contract to perform Landlord's Work and that
     Landlord itself is carrying a construction change order contingency in the
     amount of $550,000.00 in connection with the performance of Landlord's Work
     (collectively "Contingencies"). Landlord agrees that if, Landlord achieves
     a savings in such Contingencies, Landlord will, after the completion of
     Landlord's Work create a reserve fund ("Reserve Fund") equal to the lesser
     of: (i) $900,000.00, or (ii) fifty

                                     -13-
<PAGE>

     percent (50%) of the amount of such savings in such Contingencies. The
     Reserve Fund shall be used for the payment of improvements to the Property
     which may be mutually agreed upon by Landlord and Tenant (each acting
     reasonably) during the initial Lease Term or during any Extended Term;
     however, to the extent that the Reserve Fund is not used for such
     improvements, then the entire balance of the Reserve Fund shall, upon the
     termination of the Term or any Extended Term, be retained by Landlord
     solely for the benefit of Landlord.

                                   ARTICLE V
                                   ---------
                               ANNUAL FIXED RENT
                               -----------------

5.1  FIXED RENT.
     ----------

     A.  Subject to Paragraph B of this Section 5.1, Tenant agrees to pay to
     Landlord, or as directed by Landlord at such place as Landlord shall from
     time to time designate by notice, (1) commencing on the Rent Commencement
     Date, as herein defined, for each Building, and thereafter monthly, in
     advance, on the first day of each and every calendar month during the
     initial Lease Term, one-twelfth (1/12) of the Annual Fixed Rent specified
     in Section 1.3 hereof and (2) on the first day of each and every calendar
     month during each Extended Term (if exercised), one-twelfth of the Annual
     Fixed Rent as determined in Section 3.2 for the applicable Extended Term.
     Until notice of some other designation is given, Annual Fixed Rent and all
     other charges for which provision is herein made shall be paid by
     remittance to or to the order of at P.O. Box 3557, Boston, Massachusetts
     02241-3557, and all remittances received by BOSTON PROPERTIES LIMITED
     PARTNERSHIP, or by any subsequently designated recipient, shall be treated
     as a payment to Landlord.

     B.  Notwithstanding anything to the contrary herein contained:

     1.  Tenant shall have no obligation to pay Annual Fixed Rent or other
     charges with respect to any Building prior to the Rent Commencement Date
     with respect to such Building, and

     2.  If all of the Buildings do not have the same Rent Commencement Date
     and/or, in accordance with the definition of the term "Rent Year", as set
     forth in Section 1.3, all of the Buildings do not have the same Rent Year
     after the first Rent Year, then the amount of Annual Fixed Rent payable in
     respect of each Building shall be based upon a pro rata allocation to such
     Building based upon the rent schedule and the agreed upon Rentable Floor
     Area of such Building as set forth in Section 1.3.

     C.  Annual Fixed Rent for any partial month shall be paid by Tenant to
     Landlord at such rate on a pro rata basis, and, if the Rent Commencement
     Date in respect of any Building shall occur on other than the first day of
     a calendar month, the first payment of Annual Fixed Rent which Tenant shall
     make to Landlord in respect of such Building shall be a payment equal to a
     proportionate part of such monthly Annual Fixed Rent for the partial month
     from such Rent Commencement Date to the first day of the succeeding
     calendar month.

                                     -14-
<PAGE>

     D.   Additional Rent payable by Tenant on a monthly basis, as elsewhere
     provided in this Lease, likewise shall be prorated, and the first payment
     on account thereof in respect of any Building shall be determined in
     similar fashion and shall commence on the Rent Commencement Date in respect
     of such Building and other provisions of this Lease calling for monthly
     payments shall be read as incorporating this undertaking by Tenant.

     The Annual Fixed Rent and all other charges for which provision is made in
     this Lease shall be paid by Tenant to Landlord without setoff, deduction or
     abatement, except as expressly set forth in the Lease.

                                  ARTICLE VI
                                  ----------
                         TAXES AND OPERATING EXPENSES
                         ----------------------------

6.1  DEFINITIONS. With reference to the real estate taxes and Operating Expenses
     -----------
     referred to in this Article VI, it is agreed that terms used herein are
     defined as follows:

     A.   "Tax Year" means the 12-month period beginning July 1 each year during
          the Lease Term or if the appropriate Governmental tax fiscal period
          shall begin on any date other than July 1, such other date.

     B.   "Landlord's Tax Expenses" with respect to any Tax Year means the
          aggregate "real estate taxes" (hereinafter defined) with respect to
          that Tax Year, reduced by any net abatement receipts with respect to
          that Tax Year.

     C.   "Real estate taxes" means all taxes and special assessments of every
          kind and nature and user fees and other like fees assessed by any
          Governmental authority on, or, subject to the provisions of this
          Paragraph C, allocable by Landlord to, the Buildings which the
          Landlord shall be obligated to pay because of or in connection with
          the ownership, leasing or operation of the Property, less the amount
          of any abatements received by Landlord (net of the reasonable amount
          of any costs incurred by Landlord in obtaining such abatements to the
          extent that Landlord has not previously included such costs in
          Operating Expenses), and reasonable expenses of any proceedings for
          abatement of taxes. The amount of special taxes or special assessments
          to be included in real estate taxes shall be limited to the amount of
          the installment (plus any interest other than penalty interest payable
          thereon) of such special tax or special assessment required to be

                                     -15-
<PAGE>

          paid during the year in respect of which such taxes are being
          determined. There shall be excluded from such taxes interest or
          penalties on late payment of real estate taxes (except to the extent
          that such late payment is due to late payment of real estate taxes by
          Tenant), all linkage payments, special assessments imposed prior to
          the Commencement Date, and all income, estate, succession, gift,
          inheritance, corporate excise and transfer taxes; provided, however,
          that if at any time during the Lease Term the present system of ad
          valorem taxation of real property shall be changed so that in lieu of,
          or in addition to, the whole or any part of the ad valorem tax on real
          property, there shall be assessed on Landlord a capital levy or other
          tax on the gross rents received with respect to the Property, or a
          Federal, State, County, Municipal, or other local income, franchise,
          excise or similar tax, assessment, levy or charge (distinct from any
          now in effect in the jurisdiction in which the Property is located)
          measured by or based, in whole or in part, upon any such gross rents,
          then any and all of such taxes, assessments, levies or charges, to the
          extent so measured or based, shall be deemed to be included within the
          term "real estate taxes" but only to the extent that the same would be
          payable if the Property, were the only property of Landlord. To the
          extent that real estate taxes shall be payable to the taxing authority
          in installments with respect to periods less than a Tax Year, the
          statement to be furnished by Landlord shall be rendered and payments
          made on account of such installments. Real estate taxes for the Tax
          Years in which each Rent Commencement Date and the Expiration Date
          occur shall be pro-rated between Landlord and Tenant.

          D.   Landlord will, upon the written request of Tenant, either apply
          for abatements, or allow Tenant to apply for abatements in their own
          name, or in Landlord's name, at Tenant's own cost (subject to Tenant's
          right to recover such costs on a first dollar basis from the abatement
          proceeds, if any). If Tenant applies for an abatement of real estate
          taxes, then Landlord shall have the right to be involved in each step
          of the abatement process, including, without limitation, Landlord's
          right to approve all filings in connection with such abatement
          proceedings (such approval not to be unreasonably withheld) and the
          right to attend all meetings between Tenant and its representatives
          and the representatives of the Town of Needham.

6.2  OPERATING COSTS DEFINED. "Operating Expenses" means all costs and expenses
     -----------------------
     incurred by Landlord in operating, insuring, repairing, maintaining,
     replacing, and owning the Property, including those incurred in discharging
     Landlord's obligations under Article 7. Such costs shall exclude payments
     of debt service and any other mortgage charges, brokerage commissions,
     salaries of executives and owners not directly employed in the management
     or operation of the Property, the general overhead and administrative
     expenses of the home office of Landlord or Landlord's managing agent, but
     shall include, without limitation:

                                     -16-
<PAGE>

     (a)  compensation, wages and all fringe benefits, workmen's compensation
          insurance premiums and payroll taxes paid to, for or with respect to
          all persons for their services in the operating, managing (including,
          without limitation, accounting services), insuring, repairing,
          maintaining, replacing, or cleaning of the Property, provided however,
          that with respect to any individual who is not employed full time in
          performing services with respect to the Property, the costs for such
          individual shall be allocated to the Property on the basis of the
          relative time spent by such individual in performing services for the
          Property;

     (b)  payments under service contracts with independent contractors for
          operating, maintaining or cleaning of the Property;

     (c)  steam, water, sewer, gas, oil, electricity and telephone charges and
          costs of maintaining letters of credit or other security as may be
          required by utility companies as a condition of providing such
          services;

     (d)  cost of maintenance, cleaning and repairs and replacements(other than
          repairs reimbursed from contractors under warranties or guarantees);

     (e)  cost of snow removal and care of landscaping;

     (f)  cost of building and cleaning supplies and equipment;

     (g)  premiums for insurance carried with respect to the Buildings and other
          Improvements of the Property (including, without limitation, liability
          insurance, insurance against loss in case of fire or casualty and of
          monthly installments of the gross rent of the Property for a period of
          not more than twelve (12) months in the case of both, and, if there be
          any first mortgage on the Property, including such insurance as may be
          required by the holder of such first mortgage);

     (h)  intentionally omitted;

     (i)  depreciation (a) for capital expenditures made by Landlord after the
          last Rent Commencement Date to occur but only to the extent such
          improvements are required by applicable law, ordinance or regulation
          adopted after the last Rent Commencement Date to occur, and (b) for
          any capital replacement made after the expiration of the initial Lease
          Term.

          Depreciation shall (i) include an interest factor, reasonably
          determined by Landlord, as being the interest rate then charged for
          long term mortgages by institutional lenders on like properties within
          the general locality in which the Property is located, and (ii) be
          determined by dividing the

                                     -17-
<PAGE>

          original cost of such capital expenditure by the number of years of
          useful life of the capital item acquired, which useful life shall be
          determined reasonably by Landlord in accordance with generally
          accepted accounting principles and practices in effect at the time of
          acquisition of the capital item.

     (j)  Landlord's Tax Expenses, as defined in Section 6.1(c) (the parties
          hereby acknowledging that Landlord's Tax Expenses for each calendar
          year shall include the actual amount of Landlord's Tax Expenses for
          the Tax Periods included in such calendar year and that Landlord's Tax
          Expenses shall be equitably pro-rated for the calendar years in which
          each Rent Commencement Date and the Expiration Date occur);

     (k)  the cost of maintaining and replacing all signage for the Property;
          and

     (l)  all other reasonable and necessary expenses paid in connection with
          the operating, cleaning and maintenance of the Property and properly
          chargeable against income, including, without limitation, the cost of
          any maintenance or repairs which are required as the direct result of
          the act, omission, or fault of Tenant, or Tenant's agents, employees,
          contractors, licensees or invitees.

     Notwithstanding the foregoing, the following shall be excluded from
     Operating Expenses:

     (A)  Leasing fees or commissions, advertising and promotional expenses,
          legal fees in connection with lease negotiations, the cost of tenant
          improvements, build out allowances, moving expenses, assumption of
          rent under existing leases and other concessions incurred in
          connection with leasing space in the Property;

     (B)  Interest on indebtedness, debt amortization, ground rent, and
          refinancing costs for any mortgage or ground lease of the Property,
          provided however, that the foregoing shall not exclude the inclusion
          of the amortization and interest permitted to be included in Operating
          Expenses on account of capital improvements under Section 6.2(i)
          above;

     (C)  Legal, auditing, consulting and professional fees and other costs,
          (other than those legal, auditing, consulting and professional fees
          and other costs incurred in connection with the normal and routine
          maintenance and operation of the Property), including, without
          limitation, those: (i) paid or incurred in connection with financings,
          refinancings or sales of any Landlord's interest in the Property, (ii)
          relating to specific disputes with tenants, and (iii) relating to any
          special reporting required by securities laws;

                                     -18-
<PAGE>

     (D)  any management fees (see Section 6.5 for Tenant's obligation to pay
          Management Fee);

     (E)  The cost of any item or service to the extent reimbursable to Landlord
          by insurance required to be maintained under the Lease, by any tenant,
          or any third party;

     (F)  The cost of repairs or replacements incurred by reason of fire,
          casualty, or condemnation other than costs not in excess of the
          deductible on any insurance maintained by Landlord which provides a
          recovery for such repair or replacement (which deductible shall in no
          event exceed $25,000.00);

     (G)  Insurance premiums to the extent any tenant causes Landlord's existing
          insurance premiums to increase or requires Landlord to purchase
          additional insurance because of such tenant's use of the Property for
          other than office purposes;

     (H)  Any advertising, promotional or marketing expenses for the Property;

     (I)  The cost of any service or materials provided by any party related to
          Landlord, to the extent such costs exceed the reasonable cost for such
          service or materials absent such relationship in buildings similar to
          the Buildings in the vicinity of the Property;

     (J)  Payments for rented equipment, the cost of which equipment would
          constitute a capital expenditure if the equipment were purchased to
          the extent that such payments exceed the amount which could have been
          included in Operating Expenses had Landlord purchased such equipment
          rather than leasing such equipment;

     (K)  Penalties, damages, and interest for late payment or violations of any
          obligations of Landlord, including, without limitation, taxes,
          insurance, equipment leases and other past due amounts, except to the
          extent that such late payment arises from the late payment of
          Operating Expenses by Tenant;

     (L)  Contributions to charitable organizations;

     (M)  Costs incurred in removing the property of former tenants or other
          occupants of the Property;

     (N)  The cost of acquiring, installing, moving or restoring objects or art;

                                     -19-
<PAGE>

     (O)  Wages, salaries, or other compensation paid to any executive employees
          above the grade of general manager at the Property, except that if any
          such employee performs a service which would have been performed by an
          outside consultant, the compensation paid to such employee for
          performing such service shall be included in Operating Expenses, to
          the extent only that the cost of such service does not exceed
          competitive cost of such service had such service been rendered by an
          outside consultant;

     (P)  The net (i.e. net of the reasonable costs of collection) amount
          recovered by Landlord under any warranty or service agreement from any
          contractor or service provider shall be credited against Operating
          Expenses;

     (Q)  The amount of any penalty or fine incurred by Landlord due to
          Landlord's violation of any federal, state or local law or regulation,
          and any interest or penalties due for late payment by Landlord of any
          Operating Expenses, except, in either case to the extent that such
          penalties, interest or fine are due to Tenant's failure to make timely
          payment of any Operating Expenses which are required to be made by
          Tenant under this Lease;

     (R)  The costs or repairs necessitated by Landlord's gross negligence or
          willful misconduct (the parties hereby agreeing that the costs of
          repairs necessitated by Landlord's negligence shall be excluded from
          Operating Expenses to the maximum extent permitted by law);

     (S)  Expenses for any item or service which Tenant pays directly to a third
          party or separately reimburses Landlord;

     (T)  Reserves; or

     (U)  Capital replacements and improvements, except to the extent included
          in Operating Expenses pursuant to the provisions of Section 6.2(i)
          above.

6.3  TENANT'S PAYMENTS OF OPERATING EXPENSES.
     ---------------------------------------

     A.   Commencing as of first Rent Commencement Date to occur and, subject to
     Section 6.4, continuing throughout the Lease Term, Tenant shall pay to
     Landlord, as Additional Rent, all Operating Expenses incurred by Landlord
     during the Lease Term.

     B.   Subject to Paragraph C of this Section 6.3, payments by Tenant on
     account of the Operating Expenses shall be made monthly at the time and in
     the fashion herein provided for the payment of Annual Fixed Rent.  The
     amount so to be paid to Landlord shall be an amount from time to time
     reasonably estimated by Landlord to be sufficient to cover, in the
     aggregate, a sum equal to the Operating Expenses for each calendar year
     during the Lease Term.

                                     -20-
<PAGE>

     C.   Notwithstanding the foregoing, provided that, so long as, there has
     been no Event of Default by Tenant in the immediately preceding twelve
     month period, Tenant shall have the right to make payments on account of
     Real Estate Taxes directly to the Real Estate Tax collecting authority.
     Such payments shall be due and payable in installments in the amount
     required by the Real Estate Tax assessing authority on or before the later
     of: (i) ten (10) days of billing therefor by Landlord, or (ii) ten (10)
     days prior to the last day that the same may be paid to the Real Estate Tax
     collecting authority without incurring interest or penalties. Tenant shall,
     at the time that it makes any payment of Real Estate Taxes directly to the
     collecting authority simultaneously deliver reasonable evidence to Landlord
     that Tenant has made such payment.

     D.   No later than one hundred twenty (120) days after the end of the first
     calendar year or fraction thereof ending December 31 and of each succeeding
     calendar year during the Lease Term or fraction thereof at the end of the
     Lease Term, Landlord shall render Tenant a statement in reasonable detail
     and according to usual accounting practices certified by a representative
     of Landlord, showing for the preceding calendar year or fraction thereof,
     as the case may be, the Operating Expenses. Said statement to be rendered
     to Tenant also shall show for the preceding year or fraction thereof, as
     the case may be, the amounts already paid by Tenant on account of Operating
     Expenses and the amount of Operating Expenses remaining due from, or
     overpaid by, Tenant for the year or other period covered by the statement.

     If such statement shows a balance remaining due to Landlord, Tenant shall
     pay same to Landlord on or before the thirtieth (30th) day following
     receipt by Tenant of said statement. Any balance shown as due to Tenant
     shall be credited against Annual Fixed Rent next due, or refunded to Tenant
     on or before the thirtieth (30th) day following the issuance of such
     statement, if the Lease Term has then expired and Tenant has no further
     obligation to Landlord.

     To the extent that real estate taxes shall be payable to the taxing
     authority in installments with respect to periods less than a Tax Year, the
     statement to be furnished by Landlord shall be rendered and payments made
     on account of such installments.

     E.   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 Expenses:

          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.

                                     -21-
<PAGE>

          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 Expenses.

          3.   Any request for examination in respect of any calendar year may
          be made no more than one (1) year after Landlord advises Tenant of the
          actual amount of Operating Expenses in respect of such calendar year
          and provides to Tenant the year-end statement required under Paragraph
          C of this Section 6.3.

          4.   Such examination may be made only by an examiner approved by
          Landlord, which approval shall not be unreasonably withheld.  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
          Property in connection with such examination, provided however, that
          Tenant shall be permitted to share such information with each of its
          permitted subtenants so long as such subtenants execute and deliver to
          Landlord similar confidentiality agreements.

          6.   Any dispute between Landlord and Tenant as to the results of any
          such audit shall be submitted to arbitration in accordance with
          Section 16.32.

          7.   If, Tenant performs any such audit, it is determined that
          Landlord has overcharged Tenant on account of Operating Expenses by
          more than five (5%) percent, then Landlord shall reimburse Tenant for
          the reasonable out-of-pocket costs incurred by Tenant in performing
          such audit.

6.4  EFFECT OF MULTIPLE RENT COMMENCEMENT DATES
     ------------------------------------------

     Notwithstanding anything to the contrary herein contained, for the purpose
of determining the amount of Operating Expenses payable by Tenant with respect
to each Building after the first Rent Commencement Date, but prior to the date
that the Rent Commencement Dates with respect to all of the Buildings have
occurred, the parties hereby agree that Operating Expenses shall be allocated to
each of the Buildings on the following basis: Tenant shall pay (i) one hundred
(100%) percent of the actual amount of any Operating Expenses incurred with
respect to any Building for which a Rent Commencement Date has occurred, (ii)
subject to the last sentence of this Section 6.4,

                                     -22-
<PAGE>

any Operating Expenses which are incurred by Landlord on a Property-wide basis
(e.g. maintenance costs for exterior areas, insurance premiums and, if there are
no separate tax parcels for each Building, real estate taxes) shall be allocated
among each Buildings on the basis of the relative Rentable Floor Areas of the
Buildings, and (iii) any Operating Expenses with respect to the pavilion between
Building A and Building B shall be allocated one hundred (100%) percent to
Building A. The parties hereby confirm and agree that, from and after the last
Rent Commencement Date to occur, and continuing thereafter throughout the
remainder of the Term of the Lease, Tenant shall pay one hundred (100%) percent
of all Operating Costs. Notwithstanding the foregoing, from and after the first
Rent Commencement Date to occur, Tenant shall be required to pay one hundred
(100%) percent of the costs of: (x) the removal of snow and ice, (y) the cost of
exterior lighting (except to the extent that such cost is related to Landlord's
construction activities), and (z) landscaping (except to the extent that such
cost is related to Landlord's construction activities).

6.5  MANAGEMENT FEE
     --------------

     Commencing as of the first Rent Commencement Date to occur and continuing
     thereafter throughout the Lease Term, Tenant shall pay to Landlord, as
     additional rent, a management fee ("Management Fee") which is  equal to two
     and one-half (2.5%) percent of the gross rent of the Property (i.e. fixed
     rent, operating expenses and real estate taxes), from time to time.
     Management Fee shall be payable, on the first day of each month in advance
     at the same time and in the same manner as Annual Fixed Rent is payable by
     Tenant to Landlord. The monthly payments on account of Management Fee by
     Tenant, from time to time, shall be based, in part, on Landlord's
     reasonable estimates of the amount of Operating Expenses (including Real
     Estate Taxes) for the calendar year in question. At the time that the
     actual amount of Operating Expenses for any calendar year is determined,
     there shall be an adjustment in the amount of Management Fee payable for
     such calendar year, which adjustment shall be made in the same time, in the
     same manner, and subject to the same conditions as set forth in Section
     6.3.

                                  ARTICLE VII
                                  -----------

                        LANDLORD'S REPAIRS AND SERVICES
                        -------------------------------

7.1  STRUCTURAL REPAIRS. Except for damage caused by fire or casualty and by
     ------------------
     eminent domain, Landlord shall, throughout the Lease Term keep and maintain
     in first-class order, condition and repair the following portions of the
     Buildings and the other Improvements on the Property: the roof and the
     structural portions of the roof, the exterior and load bearing walls, the
     foundation, the structural columns and floor slabs and other structural
     elements of the Buildings and other Improvements on the Property.

                                     -23-
<PAGE>

7.2  OTHER REPAIRS TO BE MADE BY LANDLORD. Except for damage caused by fire or
     ------------------------------------
     casualty and by eminent domain, and except as otherwise provided in this
     Lease, Landlord agrees to keep and maintain in first-class order, condition
     and repair all paved and landscaped areas on the Property, the electrical,
     heating, ventilating, air conditioning, mechanical, plumbing and other
     Building systems equipment servicing the Premises, and the exterior of the
     Buildings and other Improvements. Without limitation, Landlord shall not be
     responsible to make any improvements or repairs to the Building or the
     Premises other than as expressly provided in Section 7.1 or in this Section
     7.2, unless expressly otherwise provided in this Lease.

7.3  SERVICES TO BE PROVIDED BY LANDLORD. Except as otherwise provided in this
     -----------------------------------
     Lease, and subject to Tenant's responsibilities in regard to electricity as
     provided in Section 7.4, Landlord agrees to furnish services, utilities,
     facilities and supplies as set forth in Exhibit C hereto equal in quality
     comparable to those customarily provided by landlords from time to time in
     first-class corporate headquarters campuses in Market Area, as defined on
     Exhibit G. In addition, Landlord agrees, upon Tenant's request, from time
     to time, to furnish, at Tenant's expense, additional Building operations
     services which are then being provided in first-class corporate
     headquarters campuses in the Market Area. Tenant shall pay for such
     additional services based upon reasonable and equitable rates from time to
     time established by Landlord and approved by Tenant (which approval shall
     not be unreasonably withheld). Landlord shall have no obligation to operate
     Tenant's cafeteria.

7.4  ELECTRICITY.
     -----------

     A.   Tenant shall contract 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.

     B.   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.

7.5  NO DAMAGE.
     ---------

     A.   No Liability. Landlord shall use reasonable efforts to minimize, and,
          ------------
     if reasonably possible, avoid the effect on Tenant's use of the Premises of
     any entry by Landlord into the Premises, any delay in making repairs,
     alterations or improvements, and any interruption of services to the
     Premises. However, to the maximum extent permitted by law, and subject to
     Tenant's rights under Section 15.6, Landlord shall not be liable to Tenant
     for any compensation or reduction of

                                     -24-
<PAGE>

      rent by reason of inconvenience or annoyance or for loss of business
      arising from the necessity of Landlord or its agents entering the Premises
      for any purposes in this Lease authorized, or for repairing the Premises
      or any portion of the Building or Property however the necessity may
      occur. In case Landlord is prevented or delayed from making any repairs,
      alterations or improvements, or furnishing any services or performing any
      other covenant or duty to be performed on Landlord's part, by reason of
      any cause reasonably beyond Landlord's control, including, without
      limitation, strike, lockout, breakdown, accident, order or regulation of
      or by any Governmental authority, or failure of supply, or inability by
      the exercise of reasonable diligence to obtain supplies, parts or
      employees necessary to furnish such services, or because of war or other
      emergency, or for any cause due directly to any act or neglect of Tenant
      or Tenant's servants, agents, employees, licensees or any person claiming
      by, through or under Tenant (such causes being referred to herein
      collectively as "Landlord's Force Majeure"), Landlord shall not be liable
      to Tenant therefor, nor, except as expressly otherwise provided in this
      Lease, shall Tenant be entitled to any abatement or reduction of rent by
      reason thereof, nor shall the same give rise to a claim in Tenant's favor
      that such failure constitutes actual or constructive, total or partial,
      eviction from the Premises. The parties hereby agree that financial
      inability shall not constitute Landlord's Force Majeure.

      B.  Stoppage of Service. Landlord reserves the right to stop any service
          -------------------
      or utility system, when necessary by reason of accident or emergency, or
      until necessary repairs have been completed; provided, however: (i) except
      in emergency situations, Landlord shall coordinate any such stoppage in
      service with Tenant's timing requirements, (ii) in emergency situations,
      Landlord shall use its best efforts to coordinate any such stoppage in
      service with Tenant's timing requirements, and (iii) that in each instance
      of stoppage, Landlord shall exercise its best efforts to eliminate the
      cause thereof.

                                 ARTICLE VIII
                                 ------------
                               TENANT'S REPAIRS
                               ----------------

8.1   TENANT'S REPAIRS AND MAINTENANCE. Tenant covenants and agrees that, from
      --------------------------------
      and after the Rent Commencement Date for any Building and until the end of
      the Lease Term, Tenant will, subject to the next following sentence, keep
      neat and clean and maintain in good order, condition and repair such
      Building and every part thereof, reasonable wear and tear excepted,
      excepting only for those repairs for which Landlord is responsible under
      the terms of Article VII of this Lease, damage by fire or casualty and as
      a consequence of the exercise of the power of eminent domain and damage
      caused by the act, omission, or fault of Landlord, Landlord's agents,
      employees, or contractors to the extent not covered by the insurance
      required to be carried by Tenant under this Lease. Notwithstanding the
      foregoing, prior to the Rent Commencement Date of a Building, Tenant shall
      have no obligation to maintain such Building pursuant to this Section 8.1.
      Tenant shall not permit or commit any waste. Tenant shall be

                                     -25-
<PAGE>

      responsible for the cost of repairs which may be made necessary by reason
      of damages to the Property by the negligence or willful misconduct of
      Tenant, or of Tenant's agents, employees, contractors, sublessees,
      licensees, concessionaires, or invitees, provided however, that the
      provisions of this sentence shall not require Tenant to pay for the repair
      or restoration damage caused by a peril covered by property/casualty
      insurance which Landlord is required to carry pursuant to the provisions
      of this Lease or which Landlord in fact carries, except to the extent of
      the lesser of: (i) $25,000.00 per occurrence, or (ii) the amount of
      Landlord's deductible under such insurance. Tenant shall maintain all its
      equipment, furniture and furnishings in good order and repair.

      If repairs are required to be made by Tenant pursuant to the terms hereof,
      Landlord may, upon reasonable advance notice, except that no notice shall
      be required in an emergency, demand that Tenant make the same forthwith,
      and if Tenant wrongfully refuses or neglects to commence such repairs and
      complete the same with reasonable dispatch after such demand, Landlord may
      (but shall not be required to do so) make or cause such repairs to be made
      and shall not be responsible to Tenant for any loss or damage that may
      accrue to Tenant's stock or business by reason thereof. If Landlord makes
      or causes such repairs to be made, Tenant agrees that Tenant will
      forthwith on demand, pay to Landlord as Additional Rent the cost thereof
      together with interest thereon at the rate specified in Section 16.21, and
      if Tenant shall default in such payment, Landlord shall have the remedies
      provided for non-payment of rent or other charges payable hereunder.

                                  ARTICLE IX
                                  ----------
                                  ALTERATIONS
                                  -----------

9.1   LANDLORD'S APPROVAL.
      -------------------

      A.  Tenant covenants and agrees not to make alterations, additions or
      improvements to the Premises, whether before or during the Lease Term,
      except in accordance with plans and specifications therefor first approved
      by Landlord in writing, which approval shall not be unreasonably withheld
      or delayed. However, Landlord's determination of matters relating to
      aesthetic issues relating to alterations, additions or improvements which
      are visible outside of the Buildings shall be in Landlord's bona fide
      business judgment. Without limiting such standard, Landlord shall not be
      deemed unreasonable for withholding approval of any alterations, additions
      or improvements which (i) in Landlord's reasonable opinion might adversely
      affect any structural or exterior element of the Building, any area or
      element outside of the Premises or any facility serving any area of the
      Building outside of the Premises; provided however, that this clause (i)
      shall not prevent Tenant from performing work or alterations after the
      Delivery Date for each Building for the purpose of installing file rooms
      or similar facilities so long as Tenant conforms to Landlord's reasonable
      requirements (e.g. as to structural

                                     -26-
<PAGE>

      reinforcement) with respect thereto and so long as Tenant pays for any
      costs associated with such work, or (ii) involve or affect the exterior
      design, size, height or other exterior dimensions of any Building.

      B.  If Landlord fails, within ten (10) days after Landlord's receipt from
      Tenant of a Tenant Alteration Request, as hereinafter defined, to respond
      in writing to such Request (i.e. either by approving such Request or by
      disapproving such Request and advising Tenant of the basis of such
      disapproval), then such Request shall conclusively be deemed to have been
      approved by Landlord. For the purposes hereof, a "Tenant Alteration
      Request" shall be defined as a written request by Tenant to perform an
      alteration, addition or improvement to the Premises which contains: (i)
      Tenant's plans and specifications describing the same, and (ii) a written
      statement, specifically referring to this Paragraph B, to the effect that
      if Landlord fails to respond to such Request within ten (10) business days
      of Landlord's receipt of such Request, Landlord shall be conclusively
      deemed to have approved such Request.

      C.  Landlord's review and approval of any such plans and specifications
      and consent to perform work described therein shall not be deemed an
      agreement by Landlord that such plans, specifications and work conform
      with applicable Legal Requirements and requirements of insurers of the
      Building (herein called "Insurance Requirements") nor deemed a waiver of
      Tenant's obligations under this Lease with respect to applicable Legal
      Requirements and Insurance Requirements nor impose any liability or
      obligation upon Landlord with respect to the completeness, design
      sufficiency or compliance of such plans, specifications and work with
      applicable Legal Requirements and Insurance Requirements.

9.1.1 CERTAIN ALTERATIONS WHICH DO NOT REQUIRE LANDLORD'S APPROVAL.
      ------------------------------------------------------------
      Notwithstanding the terms of Section 9.1, Tenant shall have the right,
      without obtaining the prior consent of Landlord, but upon at least ten
      (10) days prior written notice to Landlord, to make alterations, additions
      or improvements to the Premises where:

          (i)   the same are within the interior of the Buildings, and do not
                affect the exterior of the Premises and the Buildings;

          (ii)  the same do not affect the roof, any structural element of the
                Buildings or of the other Improvements,

          (iii) the same do not require material alteration of the mechanical,
                electrical, plumbing, heating, ventilating, air-conditioning and
                fire protection systems of the Buildings; and

                                     -27-
<PAGE>

          (iv)  Tenant shall comply with the provisions of this Lease and if
                such work increases the cost of insurance or taxes or of
                services, Tenant shall pay for any such increase in cost.

9.2   CONFORMITY OF WORK. Tenant covenants and agrees that any alterations,
      ------------------
      additions, improvements or installations made by it to or upon the
      Premises shall be done in a good and workmanlike manner and in compliance
      with all applicable Legal Requirements and Insurance Requirements now or
      hereafter in force, that materials of quality equivalent to the initial
      build-out of the Premises shall be employed therein, that the structure of
      the Building shall not be endangered or impaired thereby and that the
      Premises shall not be diminished in value thereby.

9.3   PERFORMANCE OF WORK, GOVERNMENTAL PERMITS AND INSURANCE. All of Tenant's
      -------------------------------------------------------
      alterations and additions and installation of furnishings, fixtures and
      equipment shall be coordinated with any work being performed by or for
      Landlord and in such manner as to maintain harmonious labor relations and
      not to damage the Building or Property or interfere with Building
      construction or operation and, except for installation of furnishings,
      shall be performed by Landlord's general contractor or by contractors or
      workmen first approved by Landlord, which approval shall not be
      unreasonably withheld. Except for work by Landlord's general contractor,
      Tenant shall procure all necessary governmental permits before making any
      repairs, alterations, other improvements or installations. Subject to
      Section 13.4, Tenant agrees to save harmless and indemnify Landlord from
      any and all injury, loss, claims or damage to any person or property
      occasioned by or arising out of the doing of any such work whether the
      same be performed prior to or during the Term of this Lease except to the
      extent caused by the negligence or willful misconduct of Landlord, its
      agents, contractors or employees. At Landlord's election, where the cost
      of such work exceeds $1,000,000.00 in any one instance, Tenant shall cause
      its contractor to maintain a payment bond in such amount and with such
      company as Landlord shall reasonably approve, and provided further that
      Landlord shall waive the requirement of obtaining a payment bond if Tenant
      demonstrates, to Landlord's reasonable satisfaction, that Tenant has funds
      or has obtained funding (or commitments for funding) sufficient to pay for
      the work in question. In addition, Tenant shall cause each contractor to
      carry worker's compensation insurance in statutory amounts covering the
      employees of all contractors and subcontractors, and commercial general
      liability insurance or comprehensive general liability insurance with a
      broad form comprehensive liability endorsement with such limits as
      Landlord may require reasonably from time to time during the Term of this
      Lease, but in no event less than such commercially reasonable amounts as
      may be reasonably required by Landlord, from time to time (all such
      insurance to be written in companies approved reasonably by Landlord and
      insuring Landlord, Landlord's managing agent and Tenant as additional
      insureds as well as contractors) and to deliver to Landlord certificates
      of all such insurance.

                                     -28-
<PAGE>

9.4   LIENS. Tenant covenants and agrees to pay promptly when due the entire
      -----
      cost of any work done on the Premises by Tenant, its agents, employees or
      contractors, and not to cause or permit any liens for labor or materials
      performed or furnished in connection therewith to attach to the Premises
      and within ten (10) business days after Tenant receives notice of such
      lien to discharge or bond over any such liens which may so attach.

9.5   NATURE OF ALTERATIONS. All work, construction, repairs, alterations, other
      ---------------------
      improvements or installations made to or upon the Premises (including, but
      not limited to, the construction performed by Landlord under Article IV),
      shall become part of the Premises and shall become the property of
      Landlord and remain upon and be surrendered with the Premises as a part
      thereof upon the expiration or earlier termination of the Lease Term,
      except as follows:

      (a) All trade fixtures whether by law deemed to be a part of the realty or
          not, installed at any time or times by Tenant or any person claiming
          under Tenant shall remain the property of Tenant or persons claiming
          under Tenant and may be removed by Tenant or any person claiming under
          Tenant at any time or times during the Lease Term or any occupancy by
          Tenant thereafter and such trade fixtures which are installed after
          the Rent Commencement Date in any Building shall be removed by Tenant
          at the expiration or earlier termination of the Lease Term if so
          requested by Landlord. Tenant shall repair any damage to the Premises
          occasioned by the removal by Tenant or any person claiming under
          Tenant of any such property from the Premises.

      (b) Landlord may require Tenant to remove, at the expiration or earlier
          termination of the Lease Term, any alterations, additions or
          improvements that are not standard for general offices and which would
          increase the costs of demolishing the space for another tenant.
          Landlord agrees to make such election at the time Landlord approves
          Tenant's plans for such alterations, additions or improvements (or at
          the time Tenant gives Landlord plans and specifications for work
          performed pursuant to Section 9.1.1). Upon such removal, Tenant shall
          restore the Premises to their condition prior to such alterations,
          additions and improvements and repair any damage occasioned by such
          removal and restoration. Notwithstanding the foregoing, Tenant shall
          not be required to remove any portion of the Landlord's Work.

      (c) If Tenant shall make any alterations, additions or improvements to the
          Premises for which Landlord's approval is required under Section 9.1
          without obtaining such approval, then at Landlord's request at any
          time during the Lease Term, and at any event at the expiration or
          earlier termination of the Lease Term, Tenant shall remove such
          alterations, additions and improvements and restore the Premises to
          their condition

                                     -29-
<PAGE>

          prior to same and repair any damage occasioned by such removal and
          restoration. Nothing herein shall be deemed to be a consent to Tenant
          to make any such alterations, additions or improvements, the
          provisions of Section 9.1 being applicable to any such work.

                                   ARTICLE X
                                   ---------
                             INTENTIONALLY OMITTED
                             ---------------------

                                  ARTICLE XI
                                  ----------
                           CERTAIN TENANT COVENANTS
                           ------------------------

Tenant covenants during the Lease Term and for such further time as Tenant
occupies any part of the Premises:

11.1  To pay when due all Annual Fixed Rent and Additional Rent and all charges
      for utility services rendered to the Premises and service inspections
      therefor except as otherwise provided in Exhibit C and, as further
      Additional Rent, all charges for additional and special services rendered
      pursuant to Section 7.3.

11.2  Not to use and occupy the Premises for any use other than the Permitted
      Use, and not to injure or deface the Premises or the Property and not to
      permit in the Premises any auction sale, vending machine (other than for
      the use of Tenant's employees) or flammable fluids or chemicals, or
      nuisance, or the emission from the Premises of any objectionable noise or
      odor and not to use or devote the Premises or any part thereof for any
      purpose other than the Permitted Use, nor any use thereof which is
      inconsistent with the maintenance of the Property as an office campus of
      the first-class in the quality of its maintenance, use and occupancy, or
      which is improper, offensive, contrary to law or ordinance or liable to
      invalidate or increase the premiums for any insurance on the Buildings or
      the other Improvements or their contents or liable to render necessary any
      alteration or addition to the Buildings or other Improvements. Further,
      (i) Tenant shall not, nor shall Tenant permit its employees, invitees,
      agents, independent contractors, contractors, assignees or subtenants to,
      keep, maintain, store or dispose of (into the sewage or waste disposal
      system or otherwise) (except for standard office supplies in such
      quantities and used in such manner as are typically found in first-class
      business offices which are stored, handled and disposed of in accordance
      with all applicable laws) or engage in any activity which might produce or
      generate any substance which is or may hereafter be classified as a
      hazardous material, waste or substance (collectively "Hazardous
      Materials"), under federal, state or local laws, rules and regulations,
      including, without limitation, 42 U.S.C. Section 6901 et seq., 42 U.S.C.
      Section 9601 et seq., 42 U.S.C. Section 2601 et seq., 49 U.S.C. Section
      1802 et seq. and Massachusetts General Laws, Chapter 21E and the rules and
      regulations promulgated under any of the foregoing, as such laws, rules
      and regulations may be amended from time to time (collectively "Hazardous
      Materials Laws"), (ii) Tenant shall immediately notify Landlord of

                                     -30-
<PAGE>

      any incident in, on or about the Premises, the Building or the Property
      that would require the filing of a notice under any Hazardous Materials
      Laws, (iii) Tenant shall comply and shall cause its employees, invitees,
      agents, independent contractors, contractors, assignees and subtenants to
      comply with each of the foregoing and (iv) Landlord shall have the right,
      upon twenty-four (24) hours prior notice (except that no notice shall be
      required in an emergency), to make such inspections (including testing) as
      Landlord shall elect from time to time to determine that Tenant is
      complying with the foregoing.

11.3  Not without prior consent of Landlord to permit the painting or placing of
      any signs, curtains, blinds, shades, awnings, aerials or flagpoles, or the
      like, each to the extent visible from outside the Premises.

11.4  To keep the Premises equipped with all safety appliances required by law
      or ordinance or any other regulation of any public authority because of
      any use made by Tenant other than normal office use, and to procure all
      licenses and permits so required because of any use made by Tenant other
      than normal office use, and to procure all licenses and permits so
      required because of such use and, if requested by Landlord, to do any work
      so required because of such use, it being understood that the foregoing
      provisions shall not be construed to broaden in any way Tenant's Permitted
      Use.

11.5  Not to place a load upon any floor in the Premises exceeding an average
      rate of 80 pounds of live load (including partitions) per square foot of
      floor area; and not to move any safe, vault or other heavy equipment in,
      about or out of the Premises except in such manner and at such time as
      Landlord shall in each instance as Landlord shall approve (which approval
      shall not be unreasonably withheld, conditioned or delayed). Tenant's
      business machines and mechanical equipment shall be placed and maintained
      by Tenant at Tenant's expense in settings sufficient to absorb and prevent
      vibration or noise that may be transmitted to the structure of the
      Buildings or to any other space in the Buildings.

11.6  To pay promptly when due all taxes which may be imposed upon personal
      property (including, without limitation, fixtures and equipment) in the
      Premises to whomever assessed; provided however, that Tenant shall have
      the right to contest any such tax prior to payment provided that Tenant
      indemnifies, defends and holds Landlord harmless from and against any
      loss, cost or damage which Landlord may suffer as the result any deferral
      in payment by Tenant.

11.7  To pay, as Additional Rent, all reasonable costs, counsel and other fees
      incurred by Landlord in connection with the successful enforcement by
      Landlord of any obligations of Tenant under this Lease or in connection
      with any bankruptcy case involving Tenant. Tenant shall not be obligated
      to make any payment to Landlord of any 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

                                     -31-
<PAGE>

      shall pay, upon demand by Tenant, all reasonable costs and attorneys' fees
      and other 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.

11.8  Not to knowingly do or knowingly permit anything to be done in or upon the
      Premises, or bring in anything or keep anything therein, which shall
      increase the rate of insurance on the Premises or on the Property above
      the standard rate applicable to premises being occupied for the use to
      which Tenant has agreed to devote the Premises provided that Tenant shall
      not be required to make any alterations or additions to the structure,
      roof, exterior and load bearing walls, foundation, structural floor slabs
      and other structural elements of the Buildings or other Improvements
      unless the same are required by such Insurance Requirements as a result of
      or in connection with Tenant's use or occupancy of the Premises beyond
      normal use of space of this kind; and Tenant further agrees that, in the
      event that Tenant shall do any of the foregoing, Tenant will promptly pay
      to Landlord, on demand, any such increase resulting therefrom, which shall
      be due and payable as Additional Rent hereunder.

11.9  To comply with all applicable Legal Requirements now or hereafter in force
      which shall impose a duty on Landlord or Tenant relating to or as a result
      of the use or occupancy of the Premises; provided however, that Tenant's
      failure to comply with any Legal Requirement shall not be considered to be
      a default of Tenant in its obligations under the Lease unless such non-
      compliance is material in nature. Tenant shall promptly pay all fines,
      penalties and damages that may arise out of or be imposed because of its
      failure to comply with the provisions of this Section 11.9.

11.10 To comply with all of the conditions of the Special Permit ("Special
      Permit") issued on June 15, 1999 to Wellsford/Whitehall Holdings, LLC in
      response to Application No. 99-2. Without limiting the foregoing, Tenant
      shall comply with: (i) those conditions of the Special Permit which relate
      to on-street parking, (ii) the implementation and funding of a shuttle
      service to the Property, and (iii) and the implementation and funding of a
      traffic demand management plan.

                                  ARTICLE XII
                                  -----------
                           ASSIGNMENT AND SUBLETTING
                           -------------------------

12.1  RESTRICTIONS ON TRANSFER. Except as otherwise expressly provided herein,
      ------------------------
      Tenant covenants and agrees that it shall not, without obtaining
      Landlord's prior written consent, assign, mortgage, pledge, hypothecate or
      otherwise transfer this Lease and/or Tenant's interest in this Lease or
      sublet (which term, without limitation, shall include granting of
      concessions, licenses or the like) the whole or any part of the Premises.
      Any assignment, mortgage, pledge, hypothecation, transfer or subletting
      not expressly permitted in or consented to by Landlord

                                     -32-
<PAGE>

      under this Article XII shall be void, ab initio; shall be of no force and
      effect; and shall confer no rights on or in favor of third parties. In
      addition, Landlord shall be entitled to seek specific performance of or
      other equitable relief with respect to the provisions hereof.

12.2  EXCEPTIONS FOR MERGERS AND AFFILIATE TRANSACTIONS. Notwithstanding the
      -------------------------------------------------
      foregoing provisions of Section 12.1 above and the provisions of Section
      12.4 below (which shall not apply to the transactions described in this
      Section 12.2), but subject to the provisions of Sections 12.5 and 12.7:
                     ---

      A.  Tenant shall have the right to assign this Lease to any corporation,
      limited liability partnership or limited liability company, or other
      entity into which Tenant may be converted or into which it may merge (each
      of which is referred to herein as a "Successor Entity"), provided that the
      Financial Test, as hereinafter defined, is satisfied, and provided that
      such Successor Entity executes and delivers to Landlord an agreement
      confirming that it has become the Tenant and is responsible for all of the
      obligations and liabilities of the Tenant under the Lease. For the
      purposes hereof, the "Financial Test" shall be satisfied if any of the
      following conditions are satisfied: (i) the Successor Entity has a net
      worth (calculated in accordance with generally accepted accounting
      principles) as of the end of the fiscal year of such Successor Entity
      which immediately precedes the date of transfer of at least Five Hundred
      Million ($500,000,000.00) Dollars, or (ii) the Successor Entity then has a
      Shadow Rating, as defined in Section 16.15, which is at least equal to the
      first Shadow Rating which is obtained by Tenant in accordance with Section
      16.15, or (iii) the Successor Entity delivers to Landlord, at the time of
      such transfer, either an additional General Letter of Credit satisfying
      all of the conditions applicable to the original General Letter of Credit,
      as set forth in Section 16.26, or an amendment (in form reasonably
      acceptable to Landlord) to the existing General Letter of Credit
      ("Existing General Letter of Credit") then being held by Landlord, so
      that, in either case, the aggregate amount of the General Letter(s) of
      Credit then being held by Landlord shall be equal to the lesser of: (i)
      one hundred fifty (150%) percent of the amount of Annual Fixed Rent then
      payable by Tenant under this Lease, or (ii) the sum of one hundred (100%)
      percent of the Annual Fixed Rent then payable by Tenant under this Lease
      plus the amount of the Existing General Letter of Credit.

      B.  Tenant shall have the right to assign its interest in this Lease and
      to sublease the Premises, or any portion thereof, to an Affiliated Entity,
      as hereinafter defined, and provided that prior to or simultaneously with
      any such: (i) assignment, such Affiliated Entity executes and delivers to
      Landlord an agreement, in form and substance reasonably acceptable to
      Landlord, whereby such Affiliated Entity assumes all of Tenant's
      obligations under the Lease, or (ii) sublease, such Affiliated Entity
      executes and delivers to Landlord an agreement, in form and substance
      reasonably acceptable to Landlord, whereby such Affiliated

                                     -33-
<PAGE>

      Entity assumes the obligations of Tenant to the extent undertaken under
      the sublease. 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. For the purposes hereof, control shall
      mean the direct or indirect ownership of more than fifty (50%) percent of
      the beneficial interest of the entity in question. If an Affiliated Entity
      to which this Lease is assigned or to which the Premises is sublet (in
      whole or in part) shall cease to be an Affiliated Entity, such cessation
      shall be considered an assignment or subletting requiring Landlord's
      consent in accordance with all of the provisions of this Article XII
      (including, without limitation, Landlord's Termination Right pursuant to
      Section 12.3).

      C.  The parties expressly agree that a merger or consolidation whereby
      Tenant is the surviving corporation shall be permitted hereunder without
      satisfying any of the conditions set forth in Paragraph A of this Section
      12.2 and without requiring Landlord's consent.

      D.  No sublease or assignment under this Section 12.2 shall relieve Tenant
      of its obligations under the Lease.

12.3  EXCEPTION FOR CERTAIN SUBLEASES
      -------------------------------

      Notwithstanding the foregoing provisions of Section 12.1 above and the
      provisions of Section 12.4 below (which shall not apply to the
      transactions described in this Section 12.3), but subject to the
                                                    ---
      provisions of Sections 12.5 and 12.7, Tenant shall have the right, upon
      prior written notice to Landlord, but without obtaining Landlord's
      consent, to enter into Permitted Subleases, as hereinafter defined. For
      the purposes hereof, a "Permitted Sublease" shall be defined as any
      sublease of any portion or portions of the Premises, provided that: (i)
      the aggregate amount of Rentable Floor Area subleased pursuant to such
      sublease does not exceed 20,000 square feet, and (ii) the aggregate amount
      of Rentable Floor Area subleased, at any point in time, pursuant to all
      Permitted Subleases which are then in effect does not exceed 100,000
      square feet.

12.4  CONSENT OF LANDLORD.
      -------------------

      A.  With respect to any sublease or assignment where Landlord's consent is
      required, Landlord agrees, subject to the provisions of this Section 12.4
      and subject to Sections 12.5, 12.6, and 12.7, that it will not
      unreasonably withhold or delay its consent to a proposed sublease or
      assignment.

      B.  Without limiting the standard of reasonableness which is applicable to
      the granting of Landlord's consent under this Section 12.4, Landlord shall
      not be deemed to be unreasonably withholding its consent to such a
      proposed assignment or subleasing if:

                                     -34-
<PAGE>

        (1)  with respect to an assignment of Tenant's interest in this Lease,
             and with respect to a sublease of more than 100,000 square feet of
             Rentable Floor Area, the proposed assignee or subtenant does not
             possess adequate financial capability to perform the obligations of
             Tenant, to the extent undertaken in the proposed sublease or
             assignment, as and when due or required, or

        (2)  the assignee or subtenant proposes to use the Premises (or part
             thereof) for a purpose other than the purpose for which the
             Premises may be used as stated in Section 1.3 hereof, or

        (3)  there shall be existing an Event of Default (defined in Section
             15.1).

        C.   If Landlord fails, within ten (10) days after Landlord's receipt
        from Tenant of a Tenant Transfer Request, as hereinafter defined, to
        respond in writing to such Request (i.e. either by approving such
        Request or by disapproving such Request and advising Tenant of the basis
        of such disapproval), then such Request shall conclusively be deemed to
        have been approved by Landlord. For the purposes hereof, a "Tenant
        Transfer Request" shall be defined as a written request from Tenant to
        Landlord for Landlord's consent to a proposed sublease or assignment of
        Tenant's interest in the Lease which contains: (i) all information
        required pursuant to Section 12.5, and (ii) a written statement,
        specifically referring to this Paragraph C, to the effect that if
        Landlord fails to respond to such Request within ten (10) days of
        Landlord's receipt of such Request, Landlord shall be conclusively
        deemed to have approved such Request.

12.5    TENANT'S NOTICE. Tenant shall give Landlord notice of any proposed
        ---------------
        sublease or assignment, and said notice shall specify the provisions of
        the proposed assignment or subletting, including (a) the name and
        address of the proposed assignee or subtenant, (b) if applicable, such
        information as to the proposed assignee's or proposed subtenant's net
        worth and financial capability and standing as may reasonably be
        required for Landlord to make the determination referred to in Section
        12.4B(1) above (provided, however, that Landlord shall hold such
        information confidential having the right to release same to its
        officers, accountants, attorneys and mortgage lenders on a confidential
        basis), (c) all of the terms and provisions upon which the proposed
        assignment or subletting is to be made, (d) in the case of a proposed
        assignment or subletting pursuant to 12.4, all other information
        necessary to make the determination referred to in Section 12.4, and (e)
        in the case of a proposed assignment or subletting pursuant to Sections
        12.2 and 12.3 above, such information as may be reasonably required by
        Landlord to determine that such proposed assignment or subletting
        complies with the requirements of said Section 12.2 or Section 12.3, as
        the case may be.

                                     -35-
<PAGE>

12.6    PROFIT ON SUBLEASING; ASSIGNMENT; AND CERTAIN TELECOMMUNICATIONS
        ----------------------------------------------------------------
        LICENSES.
        --------

        A.   In the case of any assignment or subleasing as to which Landlord
        may consent (other than an assignment or subletting permitted under
        Section 12.2 hereof), Tenant's right to enter into such assignment or
        sublease shall be upon the express and further condition, covenant and
        agreement, and Tenant hereby covenants and agrees that, in addition to
        the Annual Fixed Rent, Additional Rent and other charges to be paid
        pursuant to this Lease, fifty percent (50%) of the "Assignment/Sublease
        Profits" (hereinafter defined), if any shall be paid to Landlord. Any
        sublease, license, or other agreement entered into by Tenant permitting
        any third party to install antenna or other telecommunications devices
        on the property shall, for the purposes of this Section 12.6, be
        considered to be a sublease and Landlord shall be entitled to fifty
        percent (50%) of the "Assignment/Sublease Profits" from such
        transaction, except that: (i) Landlord shall not be entitled to any
        Assignment/Sublease Profits if the sole purpose of the installation of
        such antennas or equipment is to serve Tenant's business operations in
        connection with its permitted use at the Property, either within the
        Premises and elsewhere, and (ii) in determining the Assignment/Sublease
        Profits for any such transaction, no portion of the Annual Fixed Rent,
        Additional Rent or other charges under this Lease shall be allocated to
        the portion of the Premises used for the installation of such equipment.

        B.   The "Assignment/Sublease Profits" shall be the excess, if any, of
        (a) the "Assignment/Sublease Net Revenues" as hereinafter defined over
        (b) the Annual Fixed Rent, Additional Rent and other charges provided in
        this Lease (provided, however, that for the purpose of calculating the
        Assignment/Sublease Profits in the case of a sublease, appropriate
        proportions in the applicable Annual Fixed Rent, Additional Rent and
        other charges under this Lease shall be made based on the percentage of
        the Premises subleased and on the terms of the sublease). The
        "Assignment/Sublease Net Revenues" shall be the fixed rent, additional
        rent and all other charges and sums payable either initially or over the
        term of the sublease or assignment plus all other profits and increases
        to be derived by Tenant as a result of such subletting or assignment,
        less the reasonable costs of Tenant incurred in such subleasing or
        assignment (the definition of which shall include but not necessarily be
        limited to rent concessions, brokerage commissions and alteration
        allowances) amortized over the term of the sublease or assignment.

        C.   All payments of the Assignment/Sublease Profits due Landlord shall
        be made within ten (10) days of receipt of same by Tenant.

12.7    ADDITIONAL CONDITIONS.
        ---------------------

        A.   It shall be a condition of the validity of any assignment or
        subletting of right under either Section 12.2 or Section 12.3 above, or
        consented to under

                                     -36-
<PAGE>

        Section 12.4 above, that both Tenant and the assignee or sublessee agree
        directly with Landlord in a separate written instrument reasonably
        satisfactory to Landlord which contains terms and provisions reasonably
        required by Landlord, including, without limitation, the agreement of
        the assignee to be bound by all the obligations of the Tenant hereunder
        and, with respect to any subletting, to the extent undertaken under the
        sublease, including, without limitation, the obligation to pay the
        Annual Fixed Rent, Additional Rent, and other amounts provided for under
        this Lease (but in the case of a subletting, such subtenant shall agree
        to be responsible only to the extent of its rental obligations under the
        sublease) including the provisions of Sections 12.1 through 12.7 hereof,
        but such assignment or subletting shall not relieve the Tenant named
        herein of any of the obligations of the Tenant hereunder, Tenant shall
        remain fully and primarily liable therefor and the liability of Tenant
        and such assignee (or subtenant, as the case may be) shall be joint and
        several. Further, and notwithstanding the foregoing, the provisions
        hereof shall not constitute a recognition of the sublease or the
        subtenant thereunder, and at Landlord's option, upon the termination of
        the Lease, the sublease shall be terminated.

        B.   As Additional Rent, Tenant shall reimburse Landlord promptly for
        reasonable out of pocket legal and other expenses incurred by Landlord
        in connection with any request by Tenant for consent to assignment or
        subletting.

        C.   If this Lease is assigned, or if the Premises or any part thereof
        is sublet or occupied by anyone other than Tenant, Landlord may upon
        prior notice to Tenant, at any time and from time to time, collect
        Annual Fixed Rent, Additional Rent, and other charges from the assignee,
        sublessee or occupant and apply the net amount collected to the Annual
        Fixed Rent, Additional Rent and other charges herein reserved, but no
        such assignment, subletting, occupancy or collection shall be deemed a
        waiver of this covenant, or a waiver of the provisions of Sections 12.1
        through 12.7 hereof, or the acceptance of the assignee, sublessee 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, the
        Tenant herein named to remain primarily liable under this Lease.
        Notwithstanding the foregoing, Landlord shall have no right to collect
        rent from sublessees and other occupants of the Premises, other than an
        assignee, unless there is an existing Event of Default under the Lease.

        D.   The consent by Landlord to an assignment or subletting under any of
        the provisions of Section 12.4 shall in no way be construed to relieve
        Tenant from obtaining the express consent in writing of Landlord to any
        further assignment or subletting.

                                     -37-
<PAGE>

                                 ARTICLE XIII
                                 ------------
             INDEMNITY AND COMMERCIAL GENERAL LIABILITY INSURANCE
             ----------------------------------------------------

13.1    TENANT'S INDEMNITY.  To the maximum extent this agreement may be made
        ------------------
        effective according to law, and subject to Section 13.4, Tenant agrees
        to indemnify and save harmless Landlord from and against all claims of
        whatever nature arising from or claimed to have arisen from:

        A.   any accident, injury or damage whatsoever caused to any person, or
        to the property of any person, occurring in any portion of the Premises
        after the Actual Substantial Completion Date for such portion of the
        Premises and until the end of the Lease Term and thereafter, provided
        that during any such period after the Lease Term Tenant or anyone acting
        by, through or under Tenant is in occupancy of the Premises or any
        portion thereof (except to the extent the same is caused by the
        negligence or willful misconduct of Landlord, Landlord's agents,
        contractors or employees); or

        B.   any accident, injury or damage occurring: (i) on any portion of the
        Premises prior to the Actual Substantial Completion Date with respect to
        such portion of the Premises to the extent arising from Tenant's access
        to such portion of the Premises or (ii) in or about such portion of the
        Premises to the extent that such accident, injury or damage results from
        the negligence or willful misconduct on the part of Tenant or of
        Tenant's contractors, licensees, agents, servants, independent
        contractors or employees, provided however, that the provisions of this
        clause B shall not require Tenant to pay for the repair or restoration
        damage caused by a peril covered by property/casualty insurance which
        Landlord is required to carry pursuant to the provisions of this Lease,
        except to the extent of the lesser of: (i) $25,000.00 per occurrence, or
        (ii) the amount of the deductible under such insurance coverage.

        C.   any losses, costs, or damages (including, without limitation,
        reasonable attorneys fees) arising from the existence of Hazardous
        Materials which are introduced to the Property after the last Rent
        Commencement Date to occur, except to the extent that such Hazardous
        Materials are introduced to the Premises after such Rent Commencement
        Date by Landlord, Landlord's agents, employees or contractors, or
        another tenant of the Property; without limiting the foregoing, Tenant's
        obligations under this Paragraph C shall apply to any losses, costs, or
        damages arising from the breach by Tenant of its obligations under
        Section 11.2; or

        D.   any claims resulting from a breach of Tenant's obligations under
        Section 9.4 of the Lease.

                                     -38-
<PAGE>

        This indemnity and hold harmless agreement shall include indemnity
        against all reasonable costs, expenses and liabilities incurred in or in
        connection with any such claim or proceeding brought thereon, and the
        defense thereof.

13.1.1. LANDLORD'S INDEMNITY.  Subject (to the maximum extent permitted by law)
        --------------------
        to the limitations on Landlord's liability set forth in this Lease,
        Landlord agrees to indemnify, defend and save harmless Tenant from and
        against any claim arising from any accident, injury or damage occurring
        on the Premises to the extent that such accident, injury or damage
        results from the negligence or willful misconduct of Landlord or
        Landlord's employees, independent contractors or agents.

        Subject to the limitations on Landlord's liability set forth in this
        Lease, this indemnity and hold harmless agreement shall include
        indemnity against all costs, expenses and liabilities reasonably
        incurred in or in connection with any such claim or proceeding brought
        thereon, and the defense thereof.

13.2    COMMERCIAL GENERAL LIABILITY INSURANCE. Tenant agrees to maintain in
        --------------------------------------
        full force for the period of time Tenant, its agents, contractors or
        employees are in occupancy of any part of the Premises and from and
        after the first Rent Commencement Date to occur, throughout the Lease
        Term of this Lease, and thereafter, so long as Tenant is in occupancy of
        any part of the Premises, a policy of commercial general liability or
        comprehensive general liability insurance written on an occurrence basis
        with a broad form comprehensive liability endorsement under which
        Landlord and Landlord's managing agent (and such other persons as are in
        privity of estate with Landlord and Landlord's managing agent as may be
        set out in notice from time to time) and Tenant are named as insureds,
        and under which the insurer agrees to indemnify and hold Landlord and
        Landlord's managing agent, and those in privity of estate with Landlord
        and Landlord's managing agent, harmless from and against all cost,
        expense and/or liability arising out of or based upon any and all
        claims, accidents, injuries and damages mentioned in Section 13.1, in
        the broadest form of such coverage from time to time available in the
        jurisdiction in which the Premises are located. Each such policy shall
        be non-cancelable and non-amendable with respect to Landlord and
        Landlord's said designees without thirty (30) days' prior notice to
        Landlord, and a duplicate original or certificate thereof shall be
        delivered to Landlord. As of the Commencement Date hereof, the minimum
        limits of liability of such insurance shall be as specified in Section
        1.3 and from time to time during the Lease Term for such higher limits,
        if any, as are carried customarily in the Market Area with respect to
        similar properties, provided however, that in no event shall such limits
        be increased more frequently than once every three (3) years. All
        insurance required to be maintained by Tenant pursuant to this Lease
        shall be maintained with responsible companies qualified to do business,
        and in good standing, in the Commonwealth of Massachusetts and which
        have a rating of at least "A-" and are within a financial size category
        of not

                                     -39-
<PAGE>

        less than "Class VIII" in the most current Best's Key Rating Guide or
        such similar rating as may be reasonably selected by Landlord if such
        Guide is no longer published.

13.3    TENANT'S PROPERTY INSURANCE. Tenant, at Tenant's expense, shall maintain
        ---------------------------
        at all times during the Term of the Lease insurance against loss or
        damage covered by the so-called "all risk" type insurance coverage with
        respect to Tenant's fixtures, equipment, goods, wares and merchandise,
        tenant improvements made by or paid for by Tenant that are removable by
        Tenant at the end of the Term, and other property of Tenant
        (collectively "Tenant's Property"). Such insurance shall be in an amount
        at least equal to the full replacement cost of Tenant's Property.

13.4    NON-SUBROGATION.  Any insurance carried by either party with respect to
        ---------------
        the Premises or property therein or occurrences thereon shall, if it can
        be so written without additional premium or with an additional premium
        which the other party agrees to pay, include a clause or endorsement
        denying to the insurer rights of subrogation against the other party to
        the extent rights have been waived by the insured prior to occurrence of
        injury or loss. Each party, notwithstanding any provisions of this Lease
        to the contrary, hereby waives any rights of recovery against the other
        for injury or loss due to hazards covered by such insurance to the
        extent of the indemnification received thereunder. This waiver of rights
        by Tenant shall apply to, and be for the benefit of, Landlord's managing
        agent.

13.5    TENANT'S RISK.  To the maximum extent that this agreement may be made
        -------------
        effective according to law, Tenant agrees to use and occupy the Premises
        and to use such other portions of the Building or the Property as Tenant
        is herein given the right to use at Tenant's own risk; and Landlord
        shall have no responsibility or liability for any loss of or damage to
        fixtures or other personal property of Tenant, unless, subject to
        Section 13.4 hereof, 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 Section 13.5, "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 Market Area, and excluding any unusually valuable or
        exotic works of art or other such property.

13.6    LANDLORD'S INSURANCE.  Landlord shall carry at all times during the Term
        --------------------
        of this Lease (i) commercial general liability insurance with respect to
        the Buildings in an amount not less than $10,000,000.00 combined single
        limit per occurrence, (ii) insurance against loss or damage with respect
        to the Buildings and the other Improvements covered by the so-called
        "all risk" type insurance coverage in an amount equal to at least the
        full replacement cost of the Buildings and the other Improvements,
        including, without limitation, all Tenant

                                     -40-
<PAGE>

        Improvement Work and other improvements made by Tenant in the Premises,
        (iii) Workers Compensation insurance with limits which satisfy statutory
        requirements for Coverage A and Employers' Liability insurance with a
        limit of not less than $500,000, (iv) automobile general liability
        insurance with a combined single limit of not less than $1,000,000, to
        the extent that the same is applicable, (v) umbrella liability insurance
        in amounts which Landlord carries for the balance of Landlord's
        portfolio of properties, and (vi) pollution liability insurance in
        amounts which Landlord carries for the balance of Landlord's portfolio
        of properties. Landlord may also maintain such other insurance as may
        from time to time be required by a mortgagee holding a mortgage lien on
        the Building, provided that such insurance is then typically carried for
        other similar buildings in the Market Area, as defined in Exhibit G.
        Further, Landlord shall also maintain such insurance against loss of
        Annual Fixed Rent and Additional Rent for twelve months (or such longer
        period of time as Landlord's mortgagee may require) and such other risks
        and perils as Landlord deems proper, provided that such insurance is
        then typically carried for other similar buildings in the Market Area,
        as defined in Exhibit G. Any and all such insurance (i) may be
        maintained under a blanket policy affecting other properties of Landlord
        and/or its affiliated business organizations, (ii) may be written with
        deductibles as determined by Landlord (not to exceed $25,000.00) and
        (iii) the premiums for which shall included in Operating Expenses,
        subject to, and in accordance with, Section 6.2.

                                  ARTICLE XIV
                                  -----------
                           FIRE, CASUALTY AND TAKING
                           -------------------------

14.1    REPAIR OF DAMAGE CAUSED BY CASUALTY. If any portion of the Premises
        -----------------------------------
        shall be damaged by fire or casualty, Landlord shall, subject to the
        provisions of this Article XIV, 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 to repair or cause to be repaired such damage. For the purposes
        of the immediately preceding sentence, the Premises, and Landlord's
        repair obligations shall include all portions of Landlord's Work.
        However, all repairs to and replacements of Tenant's trade fixtures,
        furniture and equipment shall be made by and at the expense of Tenant.
        Landlord shall, as soon as possible after it becomes aware of any such
        casualty (but, in any event, within sixty (60) days after it becomes
        aware of any such casualty), give written notice ("Landlord's Casualty
        Notice") of: (i) whether Landlord will be exercising any of its
        termination rights pursuant to Section 14.2, (ii) Landlord's reasonable
        estimate of how long it would take Landlord to repair the Premises,
        (iii) Landlord's reasonable estimate of the cost of restoration, and
        (iv) Landlord's reasonable estimate of the amount of insurance proceeds
        which will be available to Landlord for such restoration. If the Lease
        is not terminated by either party pursuant to any of the provisions of
        this Article XIV, Landlord shall commence such repair as soon as
        possible after Landlord gives Landlord's

                                     -41-
<PAGE>

        Casualty Notice, taking into account the availability of insurance
        proceeds to Landlord. If the Premises or any part thereof shall have
        been rendered unfit for use and occupation hereunder by reason of such
        damage, there shall be no abatement of the Annual Fixed Rent and other
        charges except to the extent that Landlord receives rent interruption
        insurance proceeds as the result of untenantability arising from such
        damage, so long as Landlord complies with its obligation to obtain rent
        interruption insurance under clause (ii) of Section 13.6. Tenant agrees
        to cooperate with Landlord and Landlord's mortgagee in such manner as
        Landlord may reasonably request in assisting Landlord and Landlord's
        mortgagee in collecting insurance proceeds (including rent insurance
        proceeds) due in connection with any casualty affecting the Premises. To
        the maximum extent permitted by law, Landlord shall not be liable for
        delays in the making of any such repairs which are due to Landlord's
        Force Majeure, as defined in Section 7.5, (financial inability shall not
        be deemed to constitute causes beyond Landlord's reasonable control),
        nor, to the maximum extent permitted by law, 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. Tenant shall
        have no interest in Landlord's insurance proceeds arising from any
        casualty.

14.2    LANDLORD'S TERMINATION RIGHTS IN THE EVENT OF A CASUALTY
        ---------------------------------------------------------

        A.   Termination Right Relating Based upon a Damaged Building. If (i)
        subject to Paragraph E of this Section 14.2, any Building is so damaged
        by fire or casualty (whether or not insured) during the last five years
        of the term of the Lease that the cost of restoration exceeds the
        applicable Maximum Restoration Cost, or (ii) any Building is damaged as
        the result of an uninsured casualty (i.e. any casualty for which
        Landlord is not required to carry insurance pursuant to Section 13.6)
        and, in Landlord's reasonable judgment, the cost of restoration exceeds
        $1,000,000.00, or (iii) in Landlord's reasonable judgment, there will be
        insufficient proceeds available to Landlord to restore any Building and
        such insufficiency exceeds $1,000,000.00, then, and in any of such
        events, this Lease and the term hereof may be terminated with respect to
        the portion of the Premises which are located in such Building 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 casualty. If Landlord exercises such
        termination right, then the effective termination date shall be the date
        set forth in Landlord's termination notice which shall be not less than
        thirty (30) days after the day on which such termination notice is
        received by Tenant.

        B.   Termination Right Based upon Damage to Other Improvements. If (i)
        any Improvements other than a Building are so damaged by fire or
        casualty (whether or not insured) during the last five years of the term
        of the Lease that the cost of restoration exceeds the applicable Maximum
        Restoration Cost, or (ii) any Improvements other than a Building are
        damaged as the result of an uninsured casualty and, in Landlord's
        reasonable judgment, the cost of restoration exceeds

                                     -42-
<PAGE>

        $1,000,000.00 or (iii) in Landlord's reasonable judgment, there will be
        insufficient proceeds available to Landlord to restore any Improvements
        other than a Building and such insufficiency exceeds $1,000,000.00,
        then, and in any 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 casualty. Such notice
        shall contain Landlord's reasonable estimate of the cost of restoration
        and the amount of insurance proceeds which Landlord estimates will be
        available to Landlord for such restoration. If Landlord exercises such
        termination right, then the effective termination date shall be the date
        set forth in Landlord's termination notice which shall be not less than
        thirty (30) days after the day on which such termination notice is
        received by Tenant.

        C.   Maximum Restoration Cost. For the purposes of this Section 14.2,
        the Maximum Restoration Cost shall be defined as a percentage of the
        full replacement cost of a Building or other Improvement, as the case
        may be, and shall be defined based upon the number of years left in the
        then current term of the Lease, as follows:

        Number of Years Remaining             Maximum Restoration Cost
       in then Current Term of Lease          (i.e. as a percentage of the full
                                              replacement cost of a Building or
                                              other Improvement)

        4 or more years, but less
             than 5 years                                     50%

        3 or more years, but less
             than 4 years                                     40%

        2 or more years, but less
             than 3 years                                     30%

        1 or more years, but less
             than 2 years                                     20%

            less than 1 year                                  10%

        D.   Tenant's Right to Nullify Termination by Funding Restoration Cost.
        If Landlord exercises its termination right pursuant to either clause
        (ii) or (iii) of either Paragraph A or B above, Tenant may nullify such
        exercise by giving written notice to Landlord, within thirty (30) days
        after Tenant receives Landlord's termination notice, stating that Tenant
        will fund the amount of insufficiency in insurance proceeds and by
        delivering to Landlord, at the time that it gives such notice, either a
        letter of credit in the amount of such insufficiency, as

                                     -43-
<PAGE>

       estimated by Landlord in its termination notice, in form reasonably
       acceptable to Landlord, from a bank reasonable acceptable to Landlord,
       securing such obligation, or evidence reasonably acceptable to Landlord,
       that Tenant has delivered to Landlord's first mortgagee the amount of
       such insufficiency, as estimated by Landlord in its termination notice,
       subject to an escrow agreement for the benefit of Landlord, in form
       reasonably acceptable to Landlord, whereby the funds held by the
       mortgagee shall be disbursed on a monthly basis for the purpose of paying
       for all costs incurred by Landlord in performing such restoration.

       E.   Tenant's Right to Nullify Termination by Exercising Remaining
       Extension Options. If Landlord exercises its termination right pursuant
       to clause (i) of either Paragraph A or B above, and if Tenant has any
       remaining options to extend the Term which have not lapsed unexercised,
       then Tenant may nullify the exercise of Landlord's termination right by
       giving Landlord written notice, within thirty (30) days of its receipt of
       Landlord's termination notice, irrevocably exercising its option to
       extend the term of the Lease for one (1) five (5) year Extended Term.

14.3   TENANT'S TERMINATION RIGHTS
       ---------------------------

       A.    Termination Based Upon Estimated Restoration Period. If all or any
       portion of the Premises in any Building shall be damaged or destroyed by
       fire or casualty to the extent that the such portion of the Premises is
       rendered untenantable and the operation of Tenant's business in such
       Building in the normal course is materially adversely affected, and if
       the time period ("Estimated Building Restoration Period") set forth in
       Landlord's Casualty Notice shall exceed a period of one (1) year from the
       date that the repair and restoration work commences ("Outside Building
       Restoration Period") from the date of such casualty, Tenant may elect, by
       a notice sent within thirty (30) days after notice of such estimate is
       sent to Tenant, to terminate this Lease in respect of such Building. If
       such estimate shall fall within said one (1) year limit, Tenant shall
       have no such right to terminate and Landlord shall, subject to the
       provisions of this Article XIV, proceed with due diligence and promptness
       to reasonably complete the repairs or restoration within such one (1)
       year period, subject always to delays for by reason of Landlord's Force
       Majeure, as defined in Section 7.5, and the other limitations set forth
       in this Article XIV. Notwithstanding the foregoing, if the casualty
       occurs during the last year of the term of the Lease, the Outside
       Building Restoration Period shall be one hundred twenty (120) days from
       the date of the casualty.

       B.    Termination Based Upon Actual Restoration Period. If all or any
       portion of any Building is damaged by fire or casualty to such an extent
       so as to render such portion of the Building untenantable, and the
       operation of Tenant's business in such Building in the normal course is
       materially adversely affected and if Landlord shall fail to substantially
       complete the restoration work on or before the

                                     -44-
<PAGE>

     date (the "Building Restoration Deadline Date") which is the later of: (1)
     the end of the Estimated Building Restoration Period or (2) seventeen (17)
     months after the date that such fire or casualty occurs (except that if the
     casualty occurs during the last year of the term of the Lease, said
     seventeen (17) month period shall be four (4) months, and except that, in
     the event that Landlord is prevented from completing such restoration by
     reason of Landlord's Force Majeure, as defined in Section 7.5, the Building
     Restoration Deadline Date shall be extended by a period of time which is
     the lesser of four (4) additional months or the length of time that
     Landlord is delayed in completing such repair work by Landlord's Force
     Majeure, as defined in Section 7.5) for any reason other than Tenant's
     fault, Tenant may terminate this Lease in respect of such Building by
     giving Landlord written notice as follows:

     (i)    Said notice shall be given after the Building Restoration Deadline
            Date.

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

     (iii)  If the restoration work is substantially complete within 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.

     (iv)   If the restoration work is 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.

     C.     Termination Based Upon Estimated Restoration Period with respect to
     Damage to Other Improvements. If any portion of the Improvements other than
     a Building are damaged or destroyed by fire or casualty to the extent that
     the operation of Tenant's business in the normal course in the Premises is
     materially adversely affected, and if the time period ("Estimated Other
     Improvements Restoration Period") set forth in Landlord's Casualty Notice
     shall exceed a period of one (1) year from the date that the repair and
     restoration work commences ("Outside Other Improvements Restoration
     Period") from the date of such casualty, Tenant may elect, by a notice sent
     within thirty (30) days after notice of such estimate is sent to Tenant, to
     terminate this Lease. If such estimate shall fall within said one (1) year
     limit, Tenant shall have no such right to terminate and Landlord shall,
     subject to the provisions of this Article XIV, proceed with due diligence
     and promptness to reasonably complete the repairs or restoration within
     such one (1) year period, subject always to delays for by reason of
     Landlord's Force Majeure, as defined in Section 7.5, and the other
     limitations set forth in this Article XIV. Notwithstanding the foregoing,
     if the casualty occurs during the last

                                     -45-
<PAGE>

     year of the term of the Lease, the Outside Other Improvements Restoration
     Period shall be one hundred twenty (120) days from the date of the
     casualty.

     D.     Termination Based Upon Actual Restoration Period with respect to
     Damage to Other Improvements. If any portion of the Improvements other than
     a Building are damaged by fire or casualty to the extent that the operation
     of Tenant's business in the Premises in the normal course is materially
     adversely affected, and if Landlord shall fail to substantially complete
     the restoration work on or before the date (the "Other Improvements
     Restoration Deadline Date") which is the later of: (1) the end of the
     Estimated Other Improvements Restoration Period or (2) seventeen (17)
     months after the date that such fire or casualty occurs (except that if the
     casualty occurs during the last year of the term of the Lease, said
     seventeen (17) month period shall be four (4) months, and except that, in
     the event that Landlord is prevented from completing such restoration by
     Landlord's Force Majeure, as defined in Section 7.5), the Other
     Improvements Restoration Deadline Date shall be extended by a period of
     time which is the lesser of four (4) additional months or the length of
     time that Landlord is delayed in completing such repair work by Landlord's
     Force Majeure) for any reason other than Tenant's fault, Tenant may
     terminate this Lease by giving Landlord written notice as follows:

     (i)    Said notice shall be given after the Other Improvements Restoration
            Deadline Date.

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

     (iii)  If the restoration work is substantially complete within 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.

     (iv)   If the restoration work is 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.

14.4 GENERAL PROVISIONS RELATING TO ANY CASUALTY TERMINATION.   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 Expiration Date as stated in
Section 1.3 and the Annual Fixed Rent and other charges payable under this Lease
shall be apportioned as of such date.

14.5 INTENTIONALLY OMITTED.
     ---------------------

                                     -46-
<PAGE>

14.6 TENANT'S TERMINATION RIGHTS BASED UPON TAKING.  In the event that a
     ---------------------------------------------
material part of the Premises or the means of access thereto, shall be so taken,
appropriated or condemned, so that, in Tenant's bona fide business judgment, the
continued operation of Tenant's business in the Premises is materially adversely
affected, or in the event that more than eighteen (18%) percent of the number of
parking spaces on the Land are taken, 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.  Such termination
shall be effective in accordance with Section 14.7.  Notwithstanding the
foregoing:

     A.  if the basis of the exercise by Tenant of its termination right
     pursuant to this Section 14.6 is a taking of loss of access, Landlord may
     nullify such termination by providing Tenant with substitute access which
     is reasonably acceptable to Tenant, within sixty (60) days following the
     receipt by Landlord of Tenant's termination notice, and

     B.  if the basis of the exercise by Tenant of its termination right
     pursuant to this Section 14.6 is a loss of parking spaces, Landlord may
     nullify such termination by providing Tenant with a number parking spaces
     within a reasonable distance of the Land (such distance to be subject to
     the approval of both Landlord and Tenant, which approval shall not be
     unreasonably withheld), so that the aggregate number of parking spaces
     available to Tenant (i.e. both on the Land and in such alternative
     location) is at least eighty-two (82%) percent of the number of parking
     spaces available to Tenant prior to such taking, within ninety (90) days
     following the receipt by Landlord of Tenant's termination notice.

14.7 GENERAL TAKING PROVISIONS.  Upon the giving of any notice of termination
     -------------------------
based upon a taking (i.e. by Tenant pursuant to Section 14.6), 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.  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 Expiration Date as stated in Section
1.3, and the Annual Fixed 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 substantially the same condition as obtained prior to such taking,
appropriation or condemnation in which event (i) a just proportion of the Annual
Fixed 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, (ii) a just proportion of the
remainder of the Annual Fixed Rent, according to the nature and extent of the
taking, appropriation or condemnation and the resultant injury

                                     -47-
<PAGE>

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.

14.8 TAKING PROCEEDS.
     ---------------

     A.   Except for any award specifically reimbursing Tenant for moving or
relocation expenses, and except as set forth in Paragraph C of this Section
14.8, 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.

     B.   For the purposes of Paragraph C of this Section 14.8, the following
terms shall have the following meanings:

     "Award Balance" shall be the amount, if any, by which the total
      -------------
compensation and damages awarded in respect of a permanent taking exceeds the
total of the portion of award allocable to the land on which the Buildings and
other Improvements are situated (i.e. as if the land were not improved but as
encumbered by, for example, all title matters) and all amounts payable in such
event under bona fide ground leases or underlying leases and under all bona fide
mortgages or other encumbrances which may now or hereafter be placed on,
encumber or affect the real property of which the premises are a part, or any
part of such real property.

     "Tenant's Improvements" shall be the unamortized portion (calculated on a
      ---------------------
straight-line basis over the remainder of initial Term of this Lease) of the
amount of the Tenant Payment, determined as of the date of the eminent domain
taking.

     "Book Value of Landlord's Work" shall be the unamortized cost of the
      -----------------------------
Buildings and other Improvements and related facilities (calculated on a
straight-line basis over a 40-year period), determined as of the date of the
eminent domain taking.

     C.   Notwithstanding anything to the contrary contained in the reservation
in Section 14.8, in the event of a permanent taking which results in the
termination of this Lease, Tenant shall be entitled to receive out of the Award
Balance, the amount of Tenant's Improvements, provided, however, that if the sum
of Tenant's Improvements and the Book Value of Landlord's Work exceeds Award
Balance, then Tenant's Improvements and Premises Book Value shall then be
proportionately reduced to an amount which, when added together, shall equal the
Award Balance; and, in such event, Tenant shall be entitled to receive out of
the Award Balance the amount of Tenant's Improvements as so reduced.

                                     -48-
<PAGE>

14.9  TEMPORARY TAKINGS.  In the event of any taking of the Premises or any part
      -----------------
thereof for temporary use (i.e. not in excess of one (1) year): (i) this Lease
shall be and remain unaffected thereby, and (ii) Tenant shall be entitled to
receive for itself any award made for such use, provided, that if any taking is
for a period extending beyond the Term, such award shall be apportioned between
Landlord and Tenant as of the Expiration Date or earlier termination of this
Lease.

                                  ARTICLE XV
                                  ----------
                                    DEFAULT
                                    -------

15.1  TENANT'S DEFAULT.  This Lease and the term of this Lease are subject to
      ----------------
      the limitation that Tenant shall be in default if, at any time during the
      Lease Term, any one or more of the following events (herein called an
      "Event of Default" a "default of Tenant" or similar reference) shall occur
      and not be cured prior to the expiration of the grace period (if any)
      herein provided, as follows:

      (a)  Tenant shall fail to pay any installment of the Annual Fixed Rent, or
           any Additional Rent or any other monetary amount due under this Lease
           on or before the date on which the same becomes due and payable, and
           such failure continues for fifteen (15) days after notice from
           Landlord thereof; or

      (b)  Tenant shall fail to perform or observe any other requirement, term,
           covenant or condition of this Lease (not hereinabove in this Section
           15.1 specifically referred to) on the part of Tenant to be performed
           or observed and such failure shall continue for thirty (30) days
           after notice thereof from Landlord to Tenant, or if said default
           shall reasonably require longer than thirty (30) days to cure, if
           Tenant shall fail to commence to cure said default within thirty (30)
           days after notice thereof and/or fail to continuously prosecute the
           curing of the same to completion with due diligence; or

      (c)  The estate hereby created shall be taken on execution or by other
           process of law; or

      (d)  Tenant shall make an assignment or trust mortgage arrangement, so-
           called, for the benefit of its creditors; or

      (e)  Tenant shall judicially be declared bankrupt or insolvent according
           to law; or

      (f)  a receiver, guardian, conservator, trustee in involuntary bankruptcy
           or other similar officer is appointed to take charge of all or any
           substantial part of Tenant's property by a court of competent
           jurisdiction; or

                                     -49-
<PAGE>

     (g)  any petition shall be filed against Tenant in any court, whether or
          not pursuant to any statute of the United States or of any State, in
          any bankruptcy, reorganization, composition, extension, arrangement or
          insolvency proceeding, and such proceedings shall not be fully and
          finally dismissed within one hundred twenty (120) days after the
          institution of the same; or

     (h)  Tenant shall file any petition in any court, whether or not pursuant
          to any statute of the United States or any State, in any bankruptcy,
          reorganization, composition, extension, arrangement or insolvency
          proceeding.

15.2 TERMINATION; RE-ENTRY.  Upon the happening of any one or more of the
     ---------------------
     aforementioned Events of Default (notwithstanding any license of a former
     breach of covenant or waiver of the benefit hereof or consent in a former
     instance), Landlord or Landlord's agents or servants may give to Tenant a
     notice (hereinafter called "notice of termination") terminating this Lease
     on a date specified in such notice of termination (which shall be not less
     than thirty (30) days after the date of the mailing of such notice of
     termination), and this Lease and the Lease Term, as well as any and all of
     the right, title and interest of the Tenant hereunder, shall wholly cease
     and expire on the date set forth in such notice of termination (Tenant
     hereby waiving any rights of redemption) in the same manner and with the
     same force and effect as if such date were the date originally specified
     herein for the expiration of the Lease Term, and Tenant shall then quit and
     surrender the Premises to Landlord.

     In addition or as an alternative to the giving of such notice of
     termination, Landlord or Landlord's agents or servants may, by any suitable
     action or proceeding at law, immediately or at any time thereafter re-enter
     the Premises and remove therefrom Tenant, its agents, employees, servants,
     licensees, and any subtenants and other persons, and all or any of its or
     their property therefrom, and repossess and enjoy the Premises, together
     with all additions, alterations and improvements thereto; but, in any event
     under this Section 15.2, Tenant shall remain liable as hereinafter
     provided.

     The words "re-enter" and "re-entry" as used throughout this Article XV are
     not restricted to their technical legal meanings.

15.3 CONTINUED LIABILITY; RE-LETTING.  If this Lease is terminated or if
     -------------------------------
     Landlord shall re-enter the Premises as aforesaid, or in the event of the
     termination of this Lease, or of re-entry, by or under any proceeding or
     action or any provision of law by reason of an Event of Default hereunder
     on the part of Tenant, Tenant covenants and agrees forthwith to pay and be
     liable for, on the days originally fixed herein for the payment thereof,
     amounts equal to the several

                                     -50-
<PAGE>

     installments of Annual Fixed Rent, all Additional Rent and other charges
     reserved as they would, under the terms of this Lease, become due if this
     Lease had not been terminated or if Landlord had not entered or re-entered,
     as aforesaid, and whether the Premises be relet or remain vacant, in whole
     or in part, or for a period less than the remainder of the Lease Term, or
     for the whole thereof, but, in the event the Premises be relet by Landlord,
     Tenant shall be entitled to a credit in the net amount of rent and other
     charges received by Landlord in reletting, after deduction of all
     reasonable expenses incurred in good faith in reletting the Premises
     (including, without limitation, remodeling costs, brokerage fees and the
     like), and in collecting the rent in connection therewith, in the following
     manner:

     Amounts received by Landlord after reletting shall first be applied against
     such Landlord's expenses, until the same are recovered, and until such
     recovery, Tenant shall pay, as of each day when a payment would fall due
     under this Lease, the amount which Tenant is obligated to pay under the
     terms of this Lease (Tenant's liability prior to any such reletting and
     such recovery not in any way to be diminished as a result of the fact that
     such reletting might be for a rent higher than the rent provided for in
     this Lease); when and if such expenses have been completely recovered, the
     amounts received from reletting by Landlord as have not previously been
     applied shall be credited against Tenant's obligations as of each day when
     a payment would fall due under this Lease, and only the net amount thereof
     shall be payable by Tenant.  Further, Tenant shall not be entitled to any
     credit of any kind for any period after the date when the term of this
     Lease is scheduled to expire according to its terms.

     If Landlord elects to recover damages from Tenant pursuant to this Section
     15.3, Landlord agrees to use reasonable efforts to relet the Premises after
     Tenant has vacated the entirety of the Premises in the event that the Lease
     is terminated based upon a default by Tenant hereunder.  Marketing of
     Tenant's Premises in a manner similar to the manner in which Landlord, or
     affiliates of Landlord, market other similar premises within their control
     in the Greater Boston area shall be deemed to have satisfied Landlord's
     obligation to use "reasonable efforts."  In no event shall Landlord be
     required to solicit or entertain negotiations with any other prospective
     tenants for the Premises until Landlord obtains full and complete
     possession of the Premises including, without limitation, the undisputed
     legal right to re-let the Premises free of any claim of Tenant.

15.4 LIQUIDATED DAMAGES.  Landlord may elect, as an alternative, which election
     ------------------
     shall be made within one (1) year after such termination or re-entry, to
     have Tenant pay liquidated damages, which election may be made by notice
     given to Tenant at any time after the termination of this Lease under
     Section 15.2, above, and whether or not Landlord shall have collected any
     damages as hereinbefore provided in this Article XV, and in lieu of all
     other such damages beyond the date of such notice.  Upon such notice,
     Tenant shall promptly pay to

                                     -51-
<PAGE>

     Landlord, as liquidated damages, in addition to any damages collected or
     due from Tenant from any period prior to such notice, either:

          (i)  such a sum as at the time of such notice represents the amount of
          the excess, if any, of (a) the discounted present value, at a discount
          rate equal to the Treasury bond rate ("Discount Rate") in effect at
          such time for bonds having a maturity date which is the same as the
          date that the Term of the Lease would have expired but for Tenant's
          default, of the Annual Fixed Rent, Additional Rent and other charges
          which would have been payable by Tenant under this Lease for the
          remainder of the Lease Term if the Lease terms had been fully complied
          with by Tenant, over and above (b) the discounted present value, at
          the Discount Rate, of the Annual Fixed Rent, Additional Rent and other
          charges that would be received by Landlord if the Premises were re-
          leased at the time of such notice for the remainder of the Lease Term
          at the fair market value (including provisions regarding periodic
          increases in Annual Fixed Rent if such are applicable) prevailing at
          the time of such notice; or

          (ii) an amount equal to the sum of the Annual Fixed Rent and all
          Additional Rent payable for the twelve (12) months ending as of the
          effective termination date of this Lease plus the amount of Annual
          Fixed Rent and Additional Rent of any kind accrued and unpaid at the
          time of such election plus any and all expenses which the Landlord may
          have incurred for and with respect to the collection of any of such
          rent.

     For the purposes of this Article, if Landlord elects to require Tenant to
     pay liquidated damages in accordance with this Section 15.4, the total rent
     shall be computed by assuming the Operating Expenses under Section 6.2 to
     be the same as were payable for the twelve (12) calendar months (or if less
     than twelve (12) calendar months have been elapsed since the date hereof,
     the partial year) immediately preceding such termination of re-entry.

     Nothing contained in this Lease shall limit or prejudice the right of
     Landlord to prove for and obtain in proceedings for bankruptcy or
     insolvency by reason of the termination of this Lease, an amount equal to
     the maximum allowed by any statute or rule of law in effect at the time
     when, and governing the proceeds in which, the damages are to be proved,
     whether or not the amount be greater, equal to, or less than the amount of
     the loss or damages referred to above.

15.5 INTENTIONALLY OMITTED.
     ---------------------

15.6 SELF-HELP.
     ---------

     A.  Tenant Self-Help.  If, after the Actual Substantial Completion Date
         ----------------
     with respect to any portion of the Premises, a Landlord Default, as
     hereinafter defined,

                                     -52-
<PAGE>

     shall occur with respect to such portion of the Premises, Tenant may,
     without the need of Landlord's consent, if Landlord fails to cure such
     Landlord Default within the Landlord Cure Period, as hereinafter defined,
     perform the same for the account of Landlord. Landlord shall, within thirty
     (30) days of demand therefor, reimburse Tenant the sums so paid by Tenant
     in curing such Landlord Default, together with interest thereon at the
     Interest Rate, as defined in Paragraph C of this Section 15.6, accruing
     from the date that Tenant incurs the cost in question until Landlord pays
     such cost in full. However, in no event shall Tenant have the right to
     offset against, withhold or deduct from Annual Fixed Rent or Additional
     Rent payable under this Lease for any reason relating to this Section 15.6,
     except as expressly hereinafter provided. If (i) Landlord fails to
     reimburse Tenant for the sums paid by Tenant within thirty (30) days of
     Tenant's demand therefor (such demand to include reasonable evidence of the
     costs so incurred by Tenant), and (ii) either:
                                   ---

          (x) Landlord does not, within ten (10) days of its receipt of such
          demand, give written notice to Tenant objecting to such demand and
          submitting such dispute to arbitration in accordance with Section
          16.32, or
                 --

          (y) If Landlord timely disputes Tenant's demand, then Tenant obtains
          an arbitration award against Landlord based upon such breach by
          Landlord, which award becomes final, and beyond appeal, and Landlord
          fails to pay Tenant the amount of such award within thirty (30) days
          after Tenant obtains such award,

     then, subject to the last sentence of this Paragraph A, Tenant shall have
     the right to offset the amount of such sums demanded by Tenant, or awarded
     by Tenant in arbitration, as the case may be, together with accrued
     interest, as aforesaid, against the Annual Fixed Rent and Additional Rent
     payable hereunder until offset in full. For the purposes of this Section
     15.6, a "Landlord Default" shall be defined as any default by Landlord in
     its obligations under the Lease.   Notwithstanding the foregoing, Tenant
     shall have no right, pursuant to this Paragraph A, to reduce any monthly
     installment of Base Rent by more than ten (10%) percent of the amount which
     would otherwise have been due and payable by Tenant to Landlord, unless the
     aggregate amount of such deductions over the remainder of the Lease Term
     (as it has been extended) will be insufficient to fully reimburse Tenant
     for the amount demanded by Tenant, or the amount awarded to Tenant in
     arbitration, as the case may be, in which event Tenant may effect such
     offset by making deductions from each monthly installment of Base Rent in
     equal monthly amounts over the balance of the remainder of the Lease Term.

     B.  Landlord Cure Period.  For the purposes of Paragraph A of this Section
         --------------------
     15.6, the "Landlord Cure Period" shall be defined as follows:

                                     -53-
<PAGE>

         (1)   In the event of an emergency threatening life or property, or
               Tenant's interest in this Lease, three (3) days after receipt by
               Landlord of written notice from Tenant of such default;

         (2)   In the event of any other Landlord Default, thirty (30) days
               after receipt by Landlord of written notice from Tenant of such
               Landlord Default.  Notwithstanding the foregoing, in the event
               that Landlord has commenced to cure such Landlord Default within
               said thirty (30) day period, and so long as Landlord thereafter
               diligently prosecutes such cure to completion, the thirty (30)
               day period shall be extended to such period of time as Landlord
               reasonably requires to cure such default.

     C.  Landlord Self-Help.   If Tenant shall at any time fail to make any
         ------------------
     payment or perform any act which Tenant is obligated to make or perform
     under this Lease and (except in the case of emergency) if the same
     continues unpaid or unperformed beyond applicable grace periods, then
     Landlord may, but shall not be obligated so to do, after thirty (30) days'
     notice to and demand upon Tenant, or without notice to or demand upon
     Tenant in the case of any emergency, and without waiving, or releasing
     Tenant from, any obligations of Tenant in this Lease contained, make such
     payment or perform such act which Tenant is obligated to perform under this
     Lease in such manner and to such extent as may be reasonably necessary,
     and, in exercising any such rights, pay any costs and expenses, employ
     counsel and incur and pay reasonable attorneys' fees.  All sums so paid by
     Landlord and all reasonable and necessary costs and expenses of Landlord
     incidental thereto, together with interest thereon at the annual rate
     ("Lease Rate")  equal to the sum of (a) the Base Rate from time to time
     announced by Fleet Boston Financial, N.A. or its successor as its Base Rate
     and (b) two percent (2%) (but in no event greater than the maximum rate
     permitted by applicable law), from the date of the making of such
     expenditures by Landlord, shall be deemed to be Additional Rent and, except
     as otherwise in this Lease expressly provided, shall be payable to the
     Landlord on demand, and if not promptly paid shall be added to any rent
     then due or thereafter becoming due under this Lease, and Tenant covenants
     to pay any such sum or sums with interest as aforesaid, and Landlord shall
     have (in addition to any other right or remedy of Landlord) the same rights
     and remedies in the event of the non-payment thereof by Tenant as in the
     case of default by Tenant in the payment of Annual Fixed Rent.

                                  ARTICLE XVI
                                  -----------
                           MISCELLANEOUS PROVISIONS
                           ------------------------

16.1 WAIVER.  Failure on the part of Landlord or Tenant to complain of any
     ------
     action or non-action on the part of the other, no matter how long the same
     may continue, shall never be a waiver by Tenant or Landlord, respectively,
     of any of its rights

                                     -54-
<PAGE>

      hereunder. A waiver shall be enforceable against either party only if such
      waiver is made in writing by the waiving party.

      Further, no waiver at any time of any of the provisions hereof by Landlord
      or Tenant shall be construed as a waiver of any of the other provisions
      hereof, and a waiver at any time of any of the provisions hereof shall not
      be construed as a waiver at any subsequent time of the same provisions.
      The consent or approval of Landlord or Tenant to or of any action by the
      other requiring such consent or approval shall not be construed to waive
      or render unnecessary Landlord's or Tenant's consent or approval to or of
      any subsequent similar act by the other.

      No payment by either party, or acceptance by either party, of a lesser
      amount than shall be due from Tenant to Landlord shall be treated
      otherwise than as a payment on account. The acceptance by Landlord of a
      check for a lesser amount with an endorsement or statement thereon, or
      upon any letter accompanying such check, that such lesser amount is
      payment in full, shall be given no effect, and Landlord may accept such
      check without prejudice to any other rights or remedies which Landlord may
      have against Tenant. Further, the acceptance by Landlord of Annual Fixed
      Rent, Additional Rent or any other charges paid by Tenant under this Lease
      shall not be or be deemed to be a waiver by Landlord of any default by
      Tenant, whether or not Landlord knows of such default, except for such
      defaults as to which such payment relates.

16.2  CUMULATIVE REMEDIES; SPECIFIC PERFORMANCE.  Except as expressly provided
      -----------------------------------------
      in this Lease, the specific remedies to which either party may resort
      under the terms of this Lease are cumulative and are not intended to be
      exclusive of any other remedies or means of redress which either party may
      lawfully, pursuant to the provisions of this Lease, be entitled to seek in
      case of any breach or threatened breach of any provisions of this Lease.
      In addition to the other remedies provided in this Lease, either party
      shall be entitled to the restraint by injunction of the violation or
      attempted or threatened violation of any of the covenants, conditions or
      provisions of this Lease or to seek specific performance of any such
      covenants, conditions or provisions, provided, however, that the foregoing
      shall not be construed as a confession of judgment by Tenant or Landlord,
      as the case may be.

16.3  QUIET ENJOYMENT.  Landlord agrees that, upon Tenant's paying the Annual
      ---------------
      Fixed Rent, Additional Rent and other charges herein reserved, and
      performing and observing the covenants, conditions and agreements hereof
      upon the part of Tenant to be performed and observed, Tenant shall and may
      peaceably hold and enjoy the Premises during the term of this Lease,
      without interruption or disturbance from Landlord, or anyone claiming by,
      through or under Landlord (other than Tenant itself), subject, however, to
      the terms of this Lease. This covenant shall be construed as running with
      the land to and against subsequent owners and successors in interest, and
      is not, nor shall it operate or be construed

                                     -55-
<PAGE>

      as, a personal covenant of Landlord, except to the extent of the
      Landlord's interest in the Premises, and this covenant and any and all
      other covenants of Landlord contained in this Lease shall be binding upon
      Landlord and upon such subsequent owners or successors in interest of
      Landlord's interest under this Lease, including ground or master lessees,
      to the extent of their respective interests, as and when they shall
      acquire same and then only for so long as they shall retain such interest.

16.4  SURRENDER.
      ---------

      (A) No act or thing done by Landlord during the Lease Term 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 as an acceptance of a surrender of the
      Premises prior to the termination of this Lease; provided, however, that
      the foregoing shall not apply to the delivery of keys to Landlord or its
      agents in its (or their) capacity as managing agent or for purpose of
      emergency access. In any event, however, 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.

      (B) Upon the expiration or earlier termination of the Lease Term, Tenant
      shall surrender the Premises to Landlord in the condition as required by
      Sections 8.1 and 9.5, first removing all goods and effects of Tenant and
      completing such other removals as may be permitted or required pursuant to
      Section 9.5.

      (C) All furniture, equipment and personal property which remains in the
      Buildings or elsewhere on the Premises after: (i) the expiration or prior
      termination of the term of this Lease, (ii) Tenant has vacated the
      Premises, and (iii) Landlord has given Tenant at least ten (10) days prior
      written notice that it intends to exercise its rights under this Paragraph
      C, shall be conclusively deemed to be 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, then
      Landlord may receive 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 rent or other charges payable hereunder by Tenant to
      Landlord and any damages to which Landlord may be entitled under this
      Lease and at law and in equity.

16.5  BROKERAGE.  (A)  Tenant warrants and represents that Tenant has not dealt
      ---------
      with any broker in connection with the consummation of this Lease other
      than the broker, person or firm designated in Section 1.3 hereof; and in
      the event any claim is made against the Landlord relative to Tenant's
      dealings with brokers other than the broker designated in Section 1.3
      hereof, Tenant shall defend the claim against Landlord with counsel of
      Landlord's selection and save harmless and indemnify

                                     -56-
<PAGE>

      Landlord on account of loss, cost or damage which may arise by reason of
      such claim.

      (B) Landlord warrants and represents that Landlord has not dealt with any
      broker in connection with the consummation of this Lease other than the
      broker, person or firm designated in Section 1.3 hereof; and in the event
      any claim is made against the Tenant relative to Landlord's dealings with
      brokers other than the broker designated in Section 1.3 hereof, Landlord
      shall defend the claim against Tenant with counsel of Tenant's selection
      and save harmless and indemnify Tenant on account of loss, cost or damage
      which may arise by reason of such claim.

      (C) Landlord agrees that it shall be solely responsible for the payment of
      brokerage commissions to the broker, person or firm designated in Section
      1.3 hereof, pursuant to a separate agreement.

16.6  INVALIDITY OF PARTICULAR PROVISIONS.  If any term or provision of this
      -----------------------------------
      Lease, or the application thereof to any person or circumstance shall, to
      any extent, be invalid or unenforceable, the remainder of this Lease, or
      the application of such term or provision to persons or circumstances
      other than those as to which it is held invalid or unenforceable, shall
      not be affected thereby, and each term and provision of this Lease shall
      be valid and be enforced to the fullest extent permitted by law.

16.7  PROVISIONS BINDING, ETC.  The obligations of this Lease shall run with the
      -----------------------
      land, and except as herein otherwise provided, the terms hereof shall be
      binding upon and shall inure to the benefit of the successors and assigns,
      respectively, of Landlord and Tenant and, if Tenant shall be an
      individual, upon and to his heirs, executors, administrators, successors
      and assigns. Each term and each provision of this Lease to be performed by
      Tenant shall be construed to be both a covenant and a condition. The
      reference contained to successors and assigns of Tenant is not intended to
      constitute a consent to assignment by Tenant, but has reference only to
      those instances in which either Tenant has the right, pursuant to the
      provisions of Article XII hereof to assign its interest in the Lease, or
      in which Landlord may have later given consent to a particular assignment
      as required by the provisions of Article XII hereof.

16.8  RECORDING.  Each of Landlord and Tenant agree not to record the within
      ---------
      Lease, but each party hereto agrees, on the request of the other, to
      execute a so-called Notice of Lease or short form lease in form recordable
      and complying with applicable law and reasonably satisfactory to
      Landlord's and Tenant's attorneys. In no event shall such document set
      forth the rent or other charges payable by Tenant under this Lease; and
      any such document shall expressly state that it is executed pursuant to
      the provisions contained in this Lease, and is not intended to vary the
      terms and conditions of this Lease.

                                     -57-
<PAGE>

16.9  NOTICES AND TIME FOR ACTION.  Whenever, by the terms of this Lease, notice
      ---------------------------
      shall or may be given either to Landlord or to Tenant, such notices shall
      be in writing and shall be sent by hand, registered or certified mail, or
      overnight or other commercial courier, postage or delivery charges, as the
      case may be, prepaid as follows:

          If intended for Landlord, addressed to Landlord at the address set
          forth on the first page of this Lease (or to such other address or
          addresses as may from time to time hereafter be designated by Landlord
          by like notice), with a copy to Goulston & Storrs, 400 Atlantic
          Avenue, Boston, Ma 02110, Attention: Raymond M. Kwasnick, Esq.

          If intended for Tenant, addressed to Tenant at the address set forth
          on the first page of this Lease except that from and after the first
          Rent Commencement Date to occur, the address of Tenant shall be the
          Premises (or to such other address or addresses as may from time to
          time hereafter be designated by Tenant by like notice), Attention: to
          Mr. Joseph M. Joyce, Director of Real Estate, with a copy to Hutchins,
          Wheeler & Dittmar, 101 Federal Street, Boston, Ma, 02109 Attention:
          John Griffin, Esq.

      Except as otherwise provided herein, all such notices shall be effective
      when received; provided, that (i) if receipt is refused, notice shall be
      effective upon the first occasion that such receipt is refused or (ii) if
      the notice is unable to be delivered due to a change of address of which
      no notice was given, notice shall be effective upon the date such delivery
      was attempted.

      Where provision is made for the attention of an individual or department,
      the notice shall be effective only if the wrapper in which such notice is
      sent is addressed to the attention of such individual or department.

      Any notice given by an attorney on behalf of Landlord or by Landlord's
      managing agent shall be considered as given by Landlord and shall be fully
      effective.

      Time is of the essence with respect to any and all notices and periods for
      giving of notice or taking any action thereto under this Lease.

16.10 WHEN LEASE BECOMES BINDING.  Employees or agents of Landlord have no
      --------------------------
      authority to make or agree to make a lease or any other agreement or
      undertaking in connection herewith. The submission of this document for
      examination and negotiation does not constitute an offer to lease, or a
      reservation of, or option for, the Premises, and this document shall
      become effective and binding only upon the execution and delivery hereof
      by both Landlord and

                                     -58-
<PAGE>

      Tenant. All negotiations, considerations, representations and
      understandings between Landlord and Tenant are incorporated herein and may
      be modified or altered only by written agreement between Landlord and
      Tenant, and no act or omission of any employee or agent of Landlord shall
      alter, change or modify any of the provisions hereof.

16.11 PARAGRAPH HEADINGS.  The paragraph headings throughout this instrument
      ------------------
      are for convenience and reference only, and the words contained therein
      shall in no way be held to explain, modify, amplify or aid in the
      interpretation, construction or meaning of the provisions of this Lease.

16.12 RIGHTS OF MORTGAGEE.  This Lease shall be subject and subordinate to any
      -------------------
      mortgage now or hereafter on the Property (or any part thereof) or the
      Buildings, or both, and to all renewals, modifications, consolidations,
      replacements and extensions thereof and all substitutions therefor,
      provided that the holder of such mortgage agrees, by a written instrument
      ("SNDA") in the customary form required by such mortgagee as amended by
      such commercially reasonable changes as Tenant may request and the
      mortgagee may reasonably approve, to recognize the right of Tenant to use
      and occupy the Premises and exercise all other rights and privileges under
      the Lease upon the payment of rent and other charges payable by Tenant
      under this Lease and the performance by Tenant of Tenant's obligations
      hereunder. Tenant acknowledges and agrees that any SNDA shall require that
      Tenant provide to the holder of such mortgage written notice of any
      defaults of Landlord and commercially reasonable cure periods to be
      negotiated between Tenant and such holder. In confirmation of such
      subordination and recognition, Tenant shall execute and deliver promptly
      such instruments of subordination and recognition. In the event that any
      mortgagee or its respective successor in title shall succeed to the
      interest of Landlord, then this Lease shall nevertheless continue in full
      force and effect and Tenant shall and does hereby agree to attorn to such
      mortgagee or successor and to recognize such mortgagee or successor as its
      landlord. If any holder of a mortgage which includes the Premises shall so
      elect, this Lease, and the rights of Tenant hereunder, shall be superior
      in right to the rights of such holder, with the same force and effect as
      if this Lease had been executed, delivered and recorded, or a statutory
      Notice hereof recorded, prior to the execution, delivery and recording of
      any such mortgage, even if Tenant had previously agreed to subordinate the
      Lease to such mortgage. The election of any such holder shall become
      effective upon either notice from such holder to Tenant in the same
      fashion as notices from Landlord to Tenant are to be given hereunder or by
      the recording in the appropriate registry or recorder's office of an
      instrument in which such holder subordinates its rights under such
      mortgage to this Lease.

16.13 INTENTIONALLY OMITTED.
      ----------------------

16.14 INTENTIONALLY OMITTED.
      ----------------------

                                     -59-
<PAGE>

16.15 LANDLORD'S FINANCING; TENANT'S SHADOW RATING.   Tenant covenants and
      ---------------------------------------------
      agrees that it shall, upon written request of Landlord, cooperate with
      Landlord, in such manner as Landlord may reasonably request in connection
      with Landlord's obtaining financing from a third party in order to enable
      to perform its obligations under the Lease. Without limiting the
      foregoing, Tenant shall, upon Landlord's written request, obtain up to two
      so-called "shadow rating" ("Shadow Rating") from a rating agency
      reasonably acceptable to Landlord (e.g. Moody's or Standard & Poors).
      Tenant's obligations under this Section 16.15 shall not be a condition
      precedent to any obligation of the Landlord under this Lease. Landlord and
      Tenant shall each pay fifty (50%) percent of the fee charged by the rating
      agency for the first Shadow Rating requested by Landlord, as aforesaid,
      and Landlord shall pay the entire fee charged by the rating agency for the
      second Shadow Rating requested by Landlord, as aforesaid.

16.16 STATUS REPORT AND FINANCIAL STATEMENTS.  Recognizing that Landlord and
      --------------------------------------
      Tenant may find it necessary to establish to third parties, such as
      accountants, banks, potential or existing mortgagees, potential purchasers
      or the like, the then current status of performance hereunder, Tenant and
      Landlord on the request of the other party (the "Requesting Party") made
      from time to time, will promptly furnish to the Requesting Party, or any
      existing or potential holder of any mortgage encumbering the Property, or
      any potential purchaser of the Property, or a prospective permitted
      assignee of Tenant's interest or a prospective permitted subtenant of the
      Premises, or any portion thereof (each an "Interested Party") a statement
      of the status of any matter pertaining to this Lease, including, without
      limitation, acknowledgments that (or the extent to which) each party is in
      compliance with its obligations under the terms of this Lease. In
      addition, in connection with a sale or refinancing of the Buildings or the
      Property, Tenant shall deliver to Landlord, or any Interested Party
      designated by Landlord, financial statements of Tenant, as reasonably
      requested by Landlord including, but not limited to, financial statements
      ("Financial Statements") for the past three (3) years, provided that in no
      event shall Landlord request such statements more often than one (1) time
      per calendar year. So long as the entity holding Tenant's interest under
      the Lease is publicly traded, Tenant may satisfy its obligation to deliver
      such Financial Statements to Landlord by delivering to Landlord the same
      financial statements which it releases to the public. If Tenant delivers
      to Landlord Financial Statements which have not been disclosed to the
      public: Landlord shall treat such Financial Statements as confidential,
      and such Financial Statements may be disclosed only (i) as required by
      court order, (ii) to prospective purchasers and lenders and to financial
      advisors, investment bankers, lawyers and accountants, (iii) as may be
      required by Legal Requirements, or (iv) in connection with litigation
      between the parties. Any such status statement or Financial Statement
      delivered by Tenant pursuant to this Section 16.16 may be relied upon by
      any Interested Party.

                                     -60-
<PAGE>

16.17  INTENTIONALLY OMITTED
       ---------------------

16.18  HOLDING OVER.  Any holding over by Tenant after the expiration of the
       ------------
       term of this Lease shall be treated as a tenancy at sufferance and shall
       be on the terms and conditions as set forth in this Lease, as far as
       applicable except that Tenant shall pay as a use and occupancy charge an
       amount equal to the Hold-Over Percentage, as hereinafter defined, of the
       Annual Fixed Rent and Additional Rent payable by Tenant during the twelve
       month period immediately preceding the expiration of the term of the
       Lease, calculated (on a daily basis) for the period measured from the day
       on which Tenant's hold-over commences and terminating on the day on which
       Tenant vacates the Premises. The "Hold-Over Percentage" shall be defined
       as 100% with respect to the first sixty (60) days after termination of
       the Term, and 150% with respect to any period of hold-over after the
       first sixty (60) days of hold-over. In addition, if such holding-over
       continues for a period of in excess of sixty (60) days, 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
       this Lease. Nothing in the foregoing nor any other term or provision of
       this Lease shall be deemed to permit Tenant to retain possession of the
       Premises or hold over in the Premises after the expiration or earlier
       termination of the Lease Term.

16.19  ENTRY BY LANDLORD.   Landlord, and its duly authorized representatives,
       -----------------
       shall, upon reasonable prior notice (except in the case of emergency),
       have the right to enter the Premises at all reasonable times (except at
       any time in the case of emergency) for the purposes of inspecting the
       condition of same and making such repairs, alterations, additions or
       improvements thereto as may be necessary if Tenant fails to do so as
       required hereunder (but the Landlord shall have no duty whatsoever to
       make any such inspections, repairs, alterations, additions or
       improvements except as otherwise provided in Articles IV and VII), and to
       show the Premises to prospective tenants during the twenty-four (24)
       months preceding expiration of the term of this Lease as it may have been
       extended and at any reasonable time during the Lease Term to show the
       Premises to prospective purchasers and mortgagees or during the existence
       of any Event of Default.

16.20  TENANT'S PAYMENTS.  Each and every payment and expenditure, other than
       -----------------
       Annual Fixed Rent, shall be deemed to be Additional Rent hereunder,
       whether or not the provisions requiring payment of such amounts
       specifically so state, and shall be payable, unless otherwise provided in
       this Lease, within thirty (30) days after written demand by Landlord, and
       in the case of the non-payment of any such amount, Landlord shall have,
       in addition to all of its other rights and remedies, all the rights and
       remedies available to Landlord hereunder or by law in the case of non-
       payment of Annual Fixed Rent. Unless expressly otherwise provided in this
       Lease, the performance and observance by Tenant of all the terms,
       covenants and

                                     -61-
<PAGE>

       conditions of this Lease to be performed and observed by Tenant shall be
       at Tenant's sole cost and expense. In the event that Tenant shall seek
       Landlord's consent or approval under this Lease, then Tenant shall
       reimburse Landlord, upon demand, as Additional Rent, for all reasonable
       costs and expenses, including legal and architectural costs and expenses,
       incurred by Landlord in processing such request, whether or not such
       consent or approval shall be given.

16.21  LATE PAYMENT.  If Landlord shall not have received any payment or
       ------------
       installment of Annual Fixed Rent or Additional Rent on or before the date
       (the "Due Date") fifteen (15) days after the date on which the same first
       becomes payable under this Lease, the amount of such payment or
       installment shall bear interest from the Due Date through and including
       the date such payment or installment is received by Landlord, at a rate
       equal to the lesser of (i) the rate announced by Fleet Boston Financial,
       N.A. (or its successor) from time to time as its prime or base rate (or
       if such rate is no longer available, a comparable rate reasonably
       selected by Landlord), plus two percent (2%), or (ii) the maximum
       applicable legal rate, if any. Such interest shall be deemed Additional
       Rent and shall be paid by Tenant to Landlord upon demand.

16.22  COUNTERPARTS.  This Lease may be executed in several counterparts, each
       ------------
       of which shall be deemed an original, and such counterparts shall
       constitute but one and the same instrument.

16.23  ENTIRE AGREEMENT.  This Lease constitutes the entire agreement between
       ----------------
       the parties hereto, Landlord's managing agent and their respective
       affiliates with respect to the subject matter hereof and thereof and
       supersedes all prior dealings between them with respect to such subject
       matter, and there are no verbal or collateral understandings, agreements,
       representations or warranties not expressly set forth in this Lease. No
       subsequent alteration, amendment, change or addition to this Lease shall
       be binding upon Landlord or Tenant, unless reduced to writing and signed
       by the party or parties to be charged therewith.

16.24  LIMITATIONS ON LANDLORD'S LIABILITY.
       -----------------------------------

       (A) Tenant shall neither assert nor seek to enforce any claim for breach
       of this Lease against any of Landlord's assets other than Landlord's
       interest in the Property and the uncollected rents, issues and profits
       therein, and, subject to the rights of any mortgagee of Landlord which is
       unrelated to Landlord, and of Landlord to use such proceeds or awards for
       reconstruction, the insurance proceeds and taking awards therefor, Tenant
       agrees to look solely to such interest for the satisfaction of any
       liability of Landlord under this Lease, it being specifically agreed that
       neither Landlord, nor any successor holder of Landlord's interest
       hereunder, nor any beneficiary of any Trust of which any person from time
       to time holding Landlord's interest is Trustee, nor any such Trustee, nor
       any member, manager, partner, director or stockholder of Landlord or of
       Boston

                                     -62-
<PAGE>

       Properties, L.P. nor Landlord's managing agent shall 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 Landlord's successors-in-interest, or to take any other
       action which shall not involve the personal liability of Landlord, or of
       any successor holder of Landlord's interest hereunder, or of any
       beneficiary of any trust of which any person from time to time holding
       Landlord's interest is Trustee, or of any such Trustee, or of any
       manager, member, partner, director or stockholder of Landlord or of
       Landlord's managing agent, to respond in monetary damages from Landlord's
       assets other than Landlord's interest in the Property, as aforesaid.

       (B) In no event shall Landlord, Boston Properties, Inc., or Boston
       Properties Limited Partnership ever be liable for any indirect or
       consequential damages or loss of profits or the like.

       (C) Landlord agrees that notwithstanding any transfer of the Property, or
       Landlord's interest in the Property, prior to the occurrence of the last
       Rent Commencement Date, Boston Properties Limited Partnership shall,
       throughout the performance of the Landlord's Work, continue to have
       either a direct or indirect interest in the ownership of the Property,
       and Boston Properties Limited Partnership will have the authority to act
       on behalf of the Landlord entity in connection with all matters relating
       to the performance of Landlord's Work and the development of the
       Property.

16.25  NO PARTNERSHIP.  The relationship of the parties hereto is that of
       --------------
       landlord and tenant and no partnership, joint venture or participation is
       hereby created.

16.26  LETTERS OF CREDIT.
       -----------------

       A.  General Letter of Credit.  Tenant shall deliver to Landlord a Letter
           -------------------------
       of Credit ("General Letter of Credit") in the amount of Eight Million
       Seven Hundred Thousand Dollars ($8,700,000.00) at the time that Tenant
       executes and delivers the Lease to Landlord. Landlord shall hold the
       General Letter of Credit throughout the Term of this Lease (including the
       Extended Terms, if exercised), unless sooner returned to Tenant as
       provided in this Section 16.26, as security for Tenant's obligation to
       pay Base Rent and Additional Rent under this Lease all obligations on the
       part of Tenant to be performed under this Lease. The Letter of Credit
       shall be in the form of an unconditional irrevocable letter of credit
       (the "General Letter of Credit") drawn on a bank which is satisfactory to
       Landlord, in Landlord's sole discretion, in the form attached hereto as
       Exhibit H-1, which General Letter of Credit shall permit one or more
       draws thereunder to be made accompanied only by certification by Landlord
       that pursuant to the terms of this Lease, Landlord is entitled to apply
       such General Letter of Credit and the proceeds thereof to the amount of
       any past due (i.e. after the giving of any applicable notice and the
       expiration of any applicable grace periods) Base Rent or Additional Rent
       and/or to any damages based upon the amount of Rent and

                                     -63-
<PAGE>

       Additional Rent payable by Tenant if the Lease is terminated based upon
       an Event of Default by Tenant or based upon the rejection of the Lease by
       Tenant in bankruptcy or similar proceedings. The General Letter of Credit
       shall be for a term of no less than one (1) year and shall in either case
       be renewed by Tenant each year thereafter and each renewal shall be
       delivered to and received by Landlord not later than thirty (30) days
       before the expiration of the then current Letter of Credit (herein called
       a "Renewal Presentation Date"). The General Letter of Credit shall be
       uncollateralized (i.e. Tenant shall have no obligation to provide
       collateral to the issuing bank in order to induce the issuing bank to
       issue the General Letter of Credit). In the event of a failure to so
       deliver such renewal General Letter of Credit on or before the applicable
       Renewal Presentation Date, Landlord shall be entitled to present the then
       existing Letter of Credit for payment and to receive the proceeds
       thereof, which proceeds shall be held by Landlord as a cash security
       deposit, subject to the terms of this Section 16.26. While Landlord holds
       such cash security deposit Landlord shall hold such deposit in a separate
       interest bearing account. If Landlord exercises its right to draw on any
       General Letter of Credit pursuant to the immediately preceding sentence
       Landlord agrees that it will accept a substitute General Letter of
       Credit, in the amount of the proceeds drawn by Landlord, conforming to
       the requirements of this Section 16.26 in exchange for such proceeds.
       Landlord shall have the right from time to time without prejudice to any
       other remedy Landlord may have on account thereof, to apply the proceeds
       of the General Letter of Credit, or any part thereof, to the amount of
       any past due (i.e. after the giving of any applicable notice and the
       expiration of any applicable grace periods) Base Rent or Additional Rent
       and/or to any damages based upon the amount of Rent and Additional Rent
       payable by Tenant if the Lease is terminated based upon an Event of
       Default by Tenant or based upon the rejection of the Lease by Tenant in
       bankruptcy or similar proceedings. In addition, in the event of a
       termination of the Lease 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 based upon the amount of Rent and Additional Rent
       payable by Tenant. 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. If Landlord so applies all or any portion of the proceeds of the
       General Letter of Credit, Tenant shall, within seven (7) days after
       notice from Landlord, deliver to Landlord a General Letter of Credit in
       the amount so drawn by Landlord, so that Landlord will again be holding
       the full amount of the General Letter of Credit then required to be
       provided by Tenant to Landlord. Provided that Tenant is not in default,
       beyond the expiration of applicable notice and grace periods, of its
       obligations under the Lease on each anniversary of the first Rent
       Commencement Date to occur, upon Tenant's request, Landlord shall pay to
       Tenant the amount of interest which has accrued on such account to the
       date of request, and Landlord shall, within ten (10) days of its receipt
       of such request pay such interest to Tenant. Neither the holder of a
       mortgage nor the ground lessor under a ground lease on property which
       includes the Premises shall ever be responsible to Tenant for the return
       or application of the General Letter

                                     -64-
<PAGE>

of Credit, whether or not it succeeds to the position of Landlord hereunder,
unless the General Letter of Credit shall have been received in hand by such
holder or ground lessor.

B.   Annual Reductions of General Letter of Credit. Commencing on the first
     ---------------------------------------------
(1/st/) anniversary of the first Rent Commencement Date to occur, and annually
thereafter during the Term on each anniversary of such Rent Commencement Date,
the amount of the General Letter of Credit shall be reduced by One Million
($1,000,000.00) Dollars until the amount of the General Letter of Credit is
equal to Three Million and 00/100 ($3,000,000.00) Dollars, at which time there
shall be no further reduction in the General Letter of Credit. Notwithstanding
the foregoing, the parties hereby agree that, if there is an increase in the
amount of the General Letter of Credit pursuant to Section 12.2, the amount of
the General Letter of Credit (as increased pursuant to Section 12.2) shall
thereafter, on each anniversary of the date of the transfer of Tenant's interest
in the Lease to the Successor Entity, be reduced by One Million ($1,000,000.00)
Dollars until the amount of the General Letter of Credit is equal to Three
Million and 00/100 ($3,000,000.00) Dollars, at which time there shall be no
further reduction in the General Letter of Credit. Such annual reductions in the
amount of the General Letter of Credit shall be effected either by: (i) Landlord
exchanging the Letter of Credit for a Letter of Credit delivered by Tenant which
reduces the amount of the Letter of Credit by $1,000,000.00), or (ii) Landlord
accepting in writing an amendment, in form reasonably to Landlord, to the
General Letter of Credit then being held by Landlord whereby the amount of such
General Letter of Credit is reduced by $1,000,000.00. It shall be an express
condition to any reduction in the General Letter of Credit pursuant to this
Paragraph B that Tenant is not then (i.e. as of the relevant anniversary date)
in default under the terms of this Lease without the benefit of notice or grace.
Notwithstanding the foregoing, if more than one Event of Default occurs in
Tenant's obligations under the Lease during the twelve month period immediately
preceding any date as of which a reduction in the amount of the General Letter
of Credit is scheduled to occur, then there shall be no reduction in the amount
of the General Letter of Credit pursuant to this Paragraph B on such scheduled
reduction date.

C.   Return of General Letter of Credit. To the extent that Landlord has not
     ----------------------------------
previously drawn upon the General Letter of Credit , 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 the General Letter of
Credit to Tenant within thirty (30) days after the termination of the term of
the Lease.

D.   TI Letter of Credit. In accordance with Section 4.1 of the Lease, Tenant
     -------------------
shall deliver to Landlord a Letter of Credit ("TI Letter of Credit") in the
amount of Sixteen Million Four Hundred Twenty-Nine Thousand Dollars
($16,429,000.00) at the time that Tenant executes and delivers the Lease to
Landlord. The TI Letter of Credit shall be in the form of an unconditional
irrevocable letter of credit (the "TI Letter of

                                     -65-
<PAGE>

      Credit") drawn on a bank reasonably satisfactory to Landlord in the form
      attached hereto as Exhibit H-2. The TI Letter of Credit shall be
      uncollateralized (i.e. Tenant shall have no obligation to provide
      collateral to the issuing bank in order to induce the issuing bank to
      issue the TI Letter of Credit). Tenant expressly acknowledges and agrees
      that Landlord shall have the right to pledge its interest in the TI Letter
      of Credit as security for any loan which Landlord may obtain in order to
      finance the Tenant Improvement Work. Neither the holder of a mortgage nor
      the ground lessor under a ground lease on property which includes the
      Premises shall never be responsible to Tenant for the return or
      application of the TI Letter of Credit, whether or not it succeeds to the
      position of Landlord hereunder, unless the TI Letter of Credit shall have
      been received in hand by such holder or ground lessor.

      E.  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.

16.27 GOVERNING LAW. This Lease shall be governed exclusively by the provisions
      -------------
      hereof and by the law of The Commonwealth of Massachusetts, as the same
      may from time to time exist.

16.28 SIGNAGE.
      -------

      A.  Subject to Tenant's obtaining Landlord's prior written consent (which
      consent shall not be unreasonably withheld or delayed) and subject to
      Tenant obtaining all necessary governmental approvals and permits, Tenant
      shall have the right, at Tenant' own cost, to install Tenant
      identification on the Property. Landlord agrees that it shall, at Tenant's
      cost, cooperate with Tenant, in such manner as Tenant may reasonably
      request, in assisting Tenant with obtaining such governmental approvals
      and permits.

      B.  Tenant shall, at the expiration or prior termination of the Term,
      remove, at Tenant's cost, all signage installed by Tenant which is visible
      from the exterior of the Buildings.

16.29 INTENTIONALLY OMITTED.
      ---------------------

16.30 LANDLORD'S CONSENT. Where any provision of the Lease does not permit one
      ------------------
      of the parties to take an action without obtaining the consent or approval
      or satisfaction of the other party, then, except as otherwise explicitly
      provided in the Lease, such consent or approval shall not be unreasonably
      withheld or delayed, provided however, that: the provisions of this
      Section 16.30 shall not apply to Article XII (the parties hereby
      acknowledging that Article XII sets forth the only conditions under which
      Landlord is required not to unreasonably withhold its consent to a
      proposed sublease or assignment by Tenant), and wherever Landlord's
      consent relates to alterations, work or signage which is visible outside

                                     -66-
<PAGE>

      of the Premises and is based upon aesthetic considerations, then
      Landlord's sole, but good faith bona fide, business judgment shall
      control.

16.31 TENANT'S RIGHT OF FIRST REFUSAL TO PURCHASE THE PROPERTY
      --------------------------------------------------------

      A.  On the conditions, which conditions Landlord may waive by written
      notice to Tenant at any time, that: (i) there is no Event of Default in
      Tenant's obligations under the Lease, both at the time that Landlord gives
      the Offer to Purchase (defined herein) and as of the Closing Date (defined
      herein), (ii) Tenant has not assigned its interest in this Lease to anyone
      other an entity which is permitted to occupy the Premises pursuant to
      Section 12.2, (iii) Tenant has not subleased more than twenty-five (25%)
      percent of the Rentable Floor Area of the Buildings other than to those
      entities which are permitted to occupy the Premises pursuant to Section
      12.2, and (iv) this Lease is still in full force or effect, Tenant shall
      have a one-time (except as set forth on Paragraph C of this Section 16.31)
      right to purchase the Property during the Term, as follows. At the time,
      if any, that Landlord receives an offer ("Third Party Offer") from a third
      party ("Third Party") to sell the Property which Landlord, in Landlord's
      sole discretion, is willing to accept from such Third Party, Landlord
      shall give to Tenant a written offer to purchase the Property ("Offer to
      Purchase"). The Offer to Purchase shall set forth the purchase price which
      Landlord is willing, in Landlord's sole discretion, to accept, the closing
      date (which shall be not earlier than 60 days after Landlord gives such
      Offer to Purchase to Tenant), and such other terms as are set forth in the
      Third Party Offer.

      B.  Notwithstanding anything to the contrary herein contained, Tenant
      shall have no right to purchase the Property, nor shall Landlord be
      required to give an Offer to Purchase in connection with: (i) any transfer
      of beneficial interests in the Landlord entity, (ii) any transfer to an
      entity which is affiliated with Landlord or which is affiliated with one
      person or entity which has a beneficial interest in Landlord as of the
      Execution Date of this Lease, (iii) any transfer to any entity in
      connection with a merger into or acquisition of Boston Properties by a
      purchaser of Boston Properties Inc. or Boston Properties Limited
      Partnership, (iv) the granting of any mortgage affecting the Property, (v)
      any conveyance by reason of the foreclosure of any mortgage affecting the
      Property, or any deed in lieu of foreclosure, or (vi) a portfolio sale
      including the Property with one or more properties owned by Boston
      Properties Limited Partnership, Boston Properties, Inc. or an affiliate of
      either Boston Properties Limited Partnership or Boston Properties, Inc..

      C.  Tenant may exercise its right to purchase the Property by giving
      written notice ("Exercise Notice") to Landlord on or before the date ten
      (10) days after the Landlord gives the Offer to Purchase to Tenant and by
      paying to Landlord a deposit ("Deposit") equal to ten (10%) percent of the
      Purchase Price. If Tenant does not timely give the Exercise Notice, or if
      Tenant does not timely pay the

                                     -67-
<PAGE>

     Deposit, then Tenant shall have no right to purchase the Property pursuant
     to this Section 16.31, unless either: (i) Landlord is willing to accept a
     Purchase Price from the Third Party which is less than ninety (90%) percent
     of the Purchase Price set forth in the Offer to Purchase, or (ii) Landlord
     does not transfer the Property to the Third Party. If either of such
     events, Landlord shall give to Tenant a new Offer to Purchase prior to
     conveying its interest in the Property to any third party, and the
     provisions of this Section 16.31 shall apply to such new Offer to Purchase
     as if such Offer to Purchase were the first Offer to Purchase given by
     Landlord to Tenant. If Tenant timely gives the Exercise Notice, then
     Landlord shall sell the Property to Tenant, and Tenant shall purchase the
     Property from Landlord upon the following terms and conditions, to the
     extent not inconsistent with the Offer to Purchase:

          1. Payment of Purchase Price The full Purchase Price (less the Deposit
             -------------------------
     previously paid by Tenant) shall be paid by certified bank check or wire
     transfer of federal funds at the time of delivery of the deed.

          2. Condition of Title and the Property; Discharge of Existing
             ----------------------------------------------------------
     Security. The Property shall be conveyed by good and sufficient quitclaim
     --------
     deed running to either Tenant, or to a nominee designated by Tenant by
     written notice to Landlord at least seven (7) days before Closing Date,
     said deed to convey good and clear record and marketable title, free from
     encumbrances except provisions of existing building and zoning laws, real
     estate taxes for the then current fiscal/tax year as are not due and
     payable on the date of delivery of the deed, any other matters affecting
     the Property as of the Execution Date of the Lease of which Tenant receives
     notice or has knowledge, and any other matters which do not materially
     adversely affect the use of the Property, as contemplated hereunder.
     Landlord may use the Purchase Price to discharge any encumbrances affecting
     the Property, provided that reasonable escrow arrangements are made so a
     nationally recognized title insurance company is willing to issue a title
     insurance policy to Tenant free of such encumbrances. The Property to
     Tenant shall be delivered in the same condition in which such Property is
     in as of the date that Landlord receives the Exercise Notice, reasonable
     wear and tear of the Property in the ordinary course of business excepted.

          3. Casualty or Taking. If, after Tenant has timely given its Exercise
             ------------------
     Notice and paid the Deposit, there is a casualty or taking which materially
     damages the Property, then, at Tenant's election, Tenant may, by written
     notice given within fifteen (15) days of such casualty or taking, either
     cancel the exercise of its option to purchase the Property (in which event,
     such cancellation shall be treated as if Tenant had failed to timely
     exercise its option to purchase the Property and, subject to the terms of
     this Section 16.31, Landlord shall return the Deposit to Tenant), or Tenant
     may elect to purchase the Property in accordance with the provisions of
     this Section 16.31 (in which event, Tenant shall accept the Property in its
     as-is condition as of the time of closing and Landlord shall assign

                                     -68-
<PAGE>

     to Tenant any portion of Landlord's insurance or taking proceeds which
     Landlord has not applied to the cost or repairing any damage to the
     Property caused by such casualty or taking). If Tenant cancels the exercise
     of its option to purchase the Property pursuant to this Subparagraph 3,
     then Tenant shall have no further right to purchase the Property pursuant
     to this Section 16.31, unless either: (i) Landlord is willing to accept a
     Purchase Price from the Third Party which is less than ninety (90%) percent
     of the Purchase Price set forth in the Offer to Purchase, or (ii) Landlord
     does not transfer the Property to the Third Party.

          4. Closing Date. The deed shall, subject to Subparagraph 5 of this
             ------------
     Paragraph C be delivered on the date set forth in the Offer to Purchase,
     unless otherwise agreed upon in writing. Time is of the essence of this
     Section 16.31.

          5. Extension of Closing Date. If Landlord is unable to give title or
             -------------------------
     make conveyance in accordance with Subparagraph 2 above, or if the Property
     does not conform with the provisions of Subparagraph 2, then Landlord shall
     use reasonable efforts (which shall not require Landlord to expend in
     excess of Twenty-Five Thousand ($25,000.00) Dollars, except that Landlord
     shall be required to remove, by bonding or otherwise, any liens, mortgages
     and other encumbrances of record which can be discharged by the payment of
     a fixed sum) to remove any defects in title or to make conveyance or to
     make the Property conform as aforesaid, and the Closing Date shall be
     extended for up to thirty (30) days.

          6. Failure to Perfect Title or Make the Property Conform. If at the
             -----------------------------------------------------
     expiration of the extended time (i.e. extended pursuant to Paragraph 5
     above), Landlord shall have failed to remove any defects in title or make
     the Property conform, as aforesaid, then, at Tenant's option, Landlord
     shall have no obligation to convey the Property, Landlord shall return the
     Deposit to Tenant, Tenant shall have no obligation to pay the Purchase
     Price, and this Section 16.31 shall be void and without further force or
     effect. If the exercise of Tenant's option to purchase the Property is
     canceled pursuant to this Subparagraph 6, then Tenant shall have no further
     right to purchase the Property pursuant to this Section 16.31, unless
     either: (i) Landlord is willing to accept a Purchase Price from the Third
     Party which is less than ninety (90%) percent of the Purchase Price set
     forth in the Offer to Purchase, or (ii) Landlord does not transfer the
     Property to the Third Party.

          7. Deliveries by Landlord
             ----------------------

          Landlord shall, on the Closing Date, deliver to Tenant the following:

          (a)  A quitclaim deed of the Property, executed on behalf of Landlord;

          (b)  An assignment and assumption Agreement with respect to its
     interest in the leases in effect in the Property executed on behalf of
     Landlord;

                                     -69-
<PAGE>

          (c)  A non-foreign persons affidavit, executed on behalf of Landlord;

          (d)  An affidavit or other arrangements reasonably satisfactory to
     Tenant's title insurance company to protect Tenant against mechanics liens
     and with respect to the rights of parties in possession other than the
     Tenant, and anyone claiming under the Tenant;

          (e)  A bill of sale with respect to all fixtures and equipment to be
     used in connection with the operation of the Property;

          (f)  IRS Form 1099-S;

          (g)  Evidence of the authority of the signatory on behalf of Landlord;
     and

          (h)  A statement from Landlord that all contracts with contractors
     supplying services to the Property on behalf of Landlord have either been
     terminated by Landlord or are terminable within one (1) year of the Closing
     Date.

          8. Deliveries by Tenant
             --------------------

          Tenant shall, on the Closing Date, deliver to Landlord the following:

          (a)  The balance of the Purchase Price;

          (b)  An assignment and assumption agreement with respect to the leases
     then in effect in the Property;

          (c)  Evidence of the authority of the signatory on behalf of Tenant.

          9. Apportionment of Taxes, Rent, and Water and Sewer Use Charges;
             --------------------------------------------------------------
     Adjustments
     -----------

          Taxes and water and sewer use charges with respect to the Property for
     the then current year shall be apportioned between Landlord and Tenant as
     of the Closing Date. If the amount of said Taxes is not known at the
     Closing Date, they shall be apportioned on the basis of Taxes assessed for
     the preceding year, with a reapportionment as soon as the new tax rate and
     valuation can be ascertained; and if the Taxes which are to be apportioned
     shall thereafter be reduced by abatement, the amount of such abatement,
     less the reasonable cost of obtaining the same shall be apportioned between
     the parties, provided that neither party shall be obligated to institute or
     prosecute proceedings for an abatement unless otherwise agreed.

                                     -70-
<PAGE>

          10. Default by Tenant. If Tenant defaults in its obligations to
              -----------------
      purchase the Property after giving a timely Exercise Notice pursuant to
      this Section 16.31, then, as Landlord's sole remedy, Landlord shall retain
      the Deposit, and Tenant shall have no further right to purchase the
      Property.

16.32 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 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.
      Notwithstanding the foregoing, the parties hereby agree that the
      arbitrator for any disputes relating to Landlord's Work shall be Brian
      McKenna, McKenna & Company, Winchester, Ma ("Initial Arbitrator"), or
      Frank Vanzler, KVA Associates, Boston, Ma if the Initial Arbitrator is not
      available. 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 Boston,
      Massachusetts. 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; 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 Commonwealth of Massachusetts 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 the expiration of the period of ten (10) 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.

16.33 CONFIDENTIALITY
      ---------------

      This Lease and the specific terms and provisions thereof may not be
      disclosed by either party to any third party without the prior written
      consent of the other party, except (i) to the extent required by judicial
      order or other governmental rules or regulations or (ii) in connection
      with a law suit or other legal proceeding between the parties or (iii) to
      their partners, attorneys, officers, directors, employees, consultants so
      long as each party informs such persons of its obligations hereunder and
      their obligations under securities laws with respect to disclosure or
      information and trading in the stock of Tenant and Landlord or its
      affiliates. Each party shall give the other reasonable notice of any event
      which may require public disclosure of any information made confidential
      hereby. Neither party shall make any public announcement or press release
      with respect to the transactions

                                     -71-
<PAGE>

     contemplated hereby without obtaining the prior written consent of the
     other party, which consent shall not be unreasonably withheld.

     [THE REMAINDER OF THIS PAGE HAS BEEN LEFT INTENTIONALLY BLANK]

                                     -72-
<PAGE>

     EXECUTED as a sealed instrument in two or more counterparts by persons or
officers hereunto duly authorized on the Execution Date set forth above.

WITNESS:                      LANDLORD:
                              Boston Properties Limited Partnership,
                              a Delaware limited partnership

                                   By:  Boston Properties, Inc.,
                                        a Delaware corporation
                                   Its: General Partner

                                   By:   /s/ James C. Rosenfeld
                                         -------------------------------
                                   Name:  James C. Rosenfeld
                                         -------------------------------
                                   Its:   Senior Vice President
                                         -------------------------------
                                         Hereunto duly authorized

WITNESS:                      TENANT:
                              Parametric Technology Corporation

                              By: /s/ Martha L. Durcan
                                  --------------------------
                                   Name:  Martha L. Durcan
                                         -------------------------------
                                   Its:   VP - Special Counsel
                                         -------------------------------
                                         Hereunto duly authorized

                                     -73-
<PAGE>

                                  EXHIBIT A-1
                                  -----------

                               LEGAL DESCRIPTION
                               -----------------

     A certain parcel of land situate in Needham, in the County of Norfolk and
Commonwealth of Massachusetts, and being shown as lots number 3 and 4 [excepting
fee in Southern Circumferential Highway (Route 128) no access and Kendrick
Street] upon plan No. 29360A, which is filed in Norfolk Registry District with
Certificate No. 67326, Book 337, the same being compiled from a plan drawn by
Cheney Engineering Co., dated July 22, 1959, and additional data on file in the
Land Registration Office, all as modified and approved by the Land Court.

Together with the right to use sewer and railroad easements and to connect with
and use spur tracks, in common with others, as set forth in a deed from Vappi
Development Company, Inc., to Georgia-Pacific Investment Company dated September
30, 1959, recorded in Book 3765, Page 122; as affected by Relocation of a
Railroad Easement dated December 14, 1959, recorded in Book 3786, Page 430; and
by Relocation of Railroad Easement dated January 31, 1961, filed as Document No.
225520.

Together with parking rights, in common with others entitled thereto, reserved
in a deed dated January 1, 1973, filed as Document No. 339362.

                            EXHIBIT A-1 -- Page -1-
<PAGE>

                                  EXHIBIT A-2
                                  -----------

                                   SITE PLAN
                                   ---------

                    (Graphical Depiction of Plan - Omitted)

                            EXHIBIT A-2 -- Page -1-
<PAGE>

                                   EXHIBIT C

                  140 KENDRICK STREET, NEEDHAM, MASSACHUSETTS
                              LANDLORD'S SERVICES

I.   CLEANING:

     Cleaning and janitor services as provided below:

     A.   Office Areas:

          Daily: (Monday through Friday, inclusive, holidays excepted).

          1.   Empty all waste receptacles and ashtrays and remove waste
               material from the Premises; wash receptacles as necessary.

          2.   Sweep and dust mop all uncarpeted areas using a dust-treated mop.

          3.   Vacuum all rugs and carpeted areas and spot clean.

          4.   Hand dust and wipe clean with treated cloths all horizontal
               surfaces, including furniture, office equipment, window sills,
               door ledges, chair rails, and convector topes, within normal
               reach.

          5.   Wash clean all water fountains and sanitize.

          6.   Move and dust under all desk equipment and telephone and replace
               same (but not computer terminals, specialized equipment or other
               materials).

          7.   Wipe clean all chrome and other bright work.

          8.   Hand dust grill work within normal reach.

          9.   Main doors to Premises shall be locked and lights shut off upon
               completion of cleaning.

          Weekly:

          1.   Dust coat racks and the like.

          2.   Spot clean entrance doors, light switches and doorways.

                              EXHIBIT C -- Page 1
<PAGE>

          Quarterly:

          1.   Render high dusting not reached in daily cleaning to include:

               a)   dusting all pictures, frames, charts, graphs and similar
                    wall hangings.

               b)   dusting of all vertical surfaces, such as walls, partitions,
                    doors and door frames, etc.

               c)   dusting all pipes, ducts and moldings.

               d)   dusting of all vertical blinds.

               e)   dust all ventilating, air conditioning, louvers and grills.

          2.   Spray buff all resilient floors.

     B.   LAVATORIES:

          Daily: (Monday through Friday, inclusive, holidays excepted).

          1.   Sweep and damp mop.

          2.   Clean all mirrors, powder shelves, dispensers and receptacles,
               bright work, flushometers, piping and toilet seat hinges.

          3.   Wash both sides of all toilet seats.

          4.   Wash all basins, bowls and urinals.

          5.   Dust and clean all powder room fixtures.

          6.   Empty and clean paper towel and sanitary disposal receptacles.

          7.   Remove waste paper and refuse.

          8.   Refill tissue holders, soap dispensers, towel dispensers,
               sanitary dispensers; materials to be furnished by Landlord.

          Monthly:

                              EXHIBIT C -- Page 2
<PAGE>

          1.   Machine scrub lavatory floors.

          2.   Wash all partitions and tile walls in lavatories.

          3.   Dust all lighting fixtures and grills in lavatories.

     C.   MAIN LOBBIES, ELEVATORS, STAIRWELLS AND COMMONCORRIDORS:

          Daily: (Monday through Friday, inclusive, holidays excepted)

          1.   Sweep and damp mop all floors, empty and clean waste receptacles,
               dispose of waste.

          2.   Clean elevators, wash or vacuum floors, wipe down walls and
               doors.

          3.   Spot clean any metal work inside lobbies.

          4.   Spot clean any metal work surrounding building entrance doors.

          5.   Sweep all stairwells and dust handrails.

          Monthly:

          1.   All resilient tile floors in public areas to be spray buffed.

     D.   WINDOW CLEANING:

          All exterior windows shall be washed on the inside and outside
          surfaces no less than three (3) times per year.

          See attached Matrix for further cleaning Shedule.

II.  HVAC:

     A.   Heating, ventilating and air conditioning equipment will be provided
          with sufficient capacity to accommodate a maximum population density
          of one (1) person per one hundred fifty (150) square feet of useable
          floor area served, and a combined lighting and standard electrical
          load of 6.5 watts per square foot of useable floor area (i.e., 1.5
          watts for lighting and 5.0 watts for power). In the event Tenant
          introduces into the Premises personnel or equipment which overloads
          the system's ability to adequately perform its proper

                              EXHIBIT C -- Page 3
<PAGE>

          functions, Landlord shall so notify Tenant in writing and
          supplementary system(s) may be required and installed by Landlord at
          Tenant's expense, if within fifteen (15) days Tenant has not modified
          its use so as not to cause such overload.

          Operating criteria of the basic system shall be as follows:

          i)   Cooling season indoor conditions of not in excess of 75 degrees
               Fahrenheit when outdoor conditions are 91 degrees Fahrenheit
               drybulb and 73 degrees Fahrenheit wetbulb.

          ii)  Heating season minimum room temperature of 74 degrees Fahrenheit
               when outdoor conditions are 6 degrees Fahrenheit drybulb.

     B.   Landlord shall provide heating, ventilating and air conditioning as
          normal seasonal changes may require during Normal Building Operating
          Hours (7:30 a.m. to 6:00 p.m., Monday through Friday, and 8:00 a.m. to
          1:00 p.m. on Saturdays, legal holidays in all cases excepted).

          If Tenant shall require air conditioning (during the air conditioning
          season) or heating or ventilating during any season outside Normal
          Building Operating Hours, Landlord shall use Landlord's best efforts
          to furnish such services for the area or areas specified by written
          request of Tenant delivered to the Building Superintendent or the
          Landlord before 3:00 p.m. of the business day preceding the extra
          usage. For such services, Tenant shall pay Landlord, as Additional
          Rent, upon receipt of billing, a sum equal to the cost incurred by
          Landlord plus the cost of make-up water and chemicals during the
          cooling season.

III. ELECTRICAL SERVICES:

     A.   Landlord shall provide electric power for a combined load of 6.5 watts
          per square foot of usable area for lighting and for office machines
          through standard receptacles for the typical office space (i.e., 1.5
          watts for lighting and 5.0 watts for power).

     B.   Landlord, at its option, may require separate metering and direct
          billing to Tenant for the electric power required for any special
          equipment (such as computer and reproduction equipment) that requires
          either 3-phase electric power or any voltage other than 120, or for
          any other usage in excess of 3.0 watts per square foot.

                              EXHIBIT C --Page 4
<PAGE>

     C.   Landlord will furnish and install, at Tenant's expense, all
          replacement lighting tubes, lamps and ballasts required by Tenant.
          Landlord will clean lighting fixtures on a regularly scheduled basis
          at Tenant's expense.

IV.  ELEVATORS:

     Provide passenger elevator service.

V.   WATER:

     Provide hot water for lavatory purposes and cold water for drinking,
     lavatory and toilet purposes.

VI.  CARD ACCESS SYSTEM:

     Landlord will provide a card access system at one entrance to each
     Building. Except for such card access system, Landlord shall have no
     obligation to provide security services to the Property.

VII. SNOW REMOVAL:

     1    The contractor shall provide labor and materials to stake all areas
          deemed necessary by Management to ensure for proper plowing and
          sanding of the complex.

     2.   All lots and raodways are to be clear of snow/ice by 6:30 a.m. and
          maintained throughout the day as necessary.

     3.   The contractor shall begin plowing at one inch (1") of snow, being
          sure that the complex's entrance, its roadway, the parking area and
          garage roof, in that specific order are addressed.

     4.   The contractor shall insure that the snow, when plowed, will not
          impede the walkways around the building.

     5.   The contractor shall sand before or during - at management's request-
          icing conditions, be it snow, ice storm, or thaw-and-frees conditions.
          Only sand may be used unless it determined that we have emergency
          conditions.

     6.   The contractor shall monitor weather conditions  and provide for the
          necessary services (plowing or sanding) to ensure the complex is
          properly prepared at all times. The contractor may be apprised of the
          conditions by contacting security.

                              EXHIBIT C -- Page 5
<PAGE>

     7.     The contractor shall make available a supervisor to meet with
            management to discuss any problems that may occur/exist.

     8.     The contractor shall report any and all accidents to management as
            soon as possible.

     9.     The contractor shall and will be responsible for all damage done to
            any tenant's vehicle or property as a result of snow removal and
            sanding activities under the contractor's responsibility.

     10.    The contractor shall be required to maintain all equipment.

     VIII.  Landscape Services
            ------------------

     A. Spring Clean Up

               1.   Remove damaged and inappropriately growing branches from any
                    trees.

               2.   Clean up beds of all winter debris and weeds and install
                    bark mulch (state quantity).

               3.   Prune all appropriate bushes to remove winter damage.

               4.   Apply pre emergent weed control.

               5.   Apply fertilizer to trees.

               6.   Rake all areas to remove accumulated debris and weeds.

               7.   Reseed grass areas where necessary.

               8.   Irrigation start-up and shut-down.

               9.   Edge all beds.

               10.  Mechanically sweep all roads and parking areas.

               11.  Dispose of all sand off-site.

     B. Annual Maintenance

                              EXHIBIT C -- Page 6
<PAGE>

               1.   Weekly moving of lawn area.

               2.   Weekly cleaning and weeding of bed areas.

               3.   Spring flower installation (state types of flowers and
                    quantities).

               4.   Summer flower installation (state types of flowers and
                    quantities.)

               5.   Fall flower installation (state types of flowers and
                    quantities).

               6.   MDC trail surrounding the Lake will receive thorough clean-
                    up, including cleaning the trail of debris, raking and
                    trimming bushes to keep park are clear.

     C.  Plant Healthcare

               1.   Application of dormant oil to trees and shrubs.

               2.   Follow-up application of insecticidal soap.

               3.   Spring application of fertilizer to trees and shrubs.

               4.   Fall application of fertilizer to trees and shrubs.
     D.  Lawn Maintenance

               1.   Mow and trim all lawns on a weekly basis beginning with the
                    last week of April to the first week of May continuing
                    through October.

               2.   All clippings to be removed from site.

               3.   All walkways and roadways will be wind swept of all lawn
                    clippings.

               4.   Spring application: Apply balanced fertilizer with pre-
                    emergent crab grass control.

               5.   Late Spring, Early Summer Application: Apply balanced
                    fertilizer with insect control, apply broadleaf weed
                    control, and spot application as needed.

               6.   Late Summer, Early Fall Application: Apply balanced

                              EXHIBIT C -- Page 7
<PAGE>

                    slow release fertilizer, apply broadleaf weed control, and
                    spot application as needed.

               7.   Fall Dormant Feeding: Apply heavy rate of fertilizer.

               8.   Apply Limestone in late fall.

               9.   Additional applications for the insect or disease problems
                    will be diagnosed and corrected.

     E. Tree and Shrub Care

               1.   Apply granulars slow release fertilizer to all shrubs and
                    ground cover.

               2.   Deep root feed all deciduous trees during the late fall.

               3.   Apply anti-deiccant to evergreens, azaleas and rhododendrons
                    to protect shrubs from winter kill and wind burn.

     F. Tree and Shrub Pruning

               1    Trim and prune all deciduous shrubs twice yearly, one in
                    early spring to remove winter kill and dead/dying branches,
                    once in June/July.

               2.   Prune all evergreen shrubs twice yearly; one in spring to
                    remove winter kill and dead/dying branches, and once in June
                    to remove new growth to maintain the natural character of
                    the plant.

               3.   Lightly prune and shape all trees up to 18 feet.

     G. Fall Clean-Up

               1.   In October through November as weather permits, rake vacuum
                    and remove leaves throughout complex. All material to be
                    disposed of off-site.

               2.   Apply anti-desiccant to shrubs.

                              EXHIBIT C -- Page 8
<PAGE>

     H. Weed Control

               1.   Weed plant beds as necessary on a weekly basis.

               2.   Apply liquid weed control to curb lines and hardscape paved
                    surfaces.

     I. Irrigation Maintenance (Start-Up and Shut-Off)

               1.   Turn on water source.

               2.   Program control clock.

               3.   Start up system, test all zones.

               4.   Shut off water source.

               5.   Turn off controller and unplug.

               6.   Blow out lines and valves.

IX.  VENDOR CONTRACTS

     Landlord will competitively bid all services to reputable contractors.
     These contracts will be reviewed yearly for both price and services. All
     contracts shall have 'for cause' terminations with manageable time frames
     to discontinue service.

                              EXHIBIT C -- Page 9
<PAGE>

                                   EXHIBIT D
                                   ---------

                             PROPERTY FLOOR PLANS
                             --------------------

                    (Graphical Depiction of Plan - Omitted)

                              EXHIBIT D -- Page 1
<PAGE>

                                   EXHIBIT E
                                   ---------

               DECLARATION AFFIXING THE COMMENCEMENT DATE, RENT
               ------------------------------------------------
                COMMENCEMENT DATE, AND EXPIRATION DATE OF LEASE
                -----------------------------------------------

     THIS AGREEMENT made this _______ day of _____________, 199__, by and
between _____________ LLC, but not individually (hereinafter "Landlord") and
Parametric Technology Corporation, a Delaware corporation (hereinafter
"Tenant").

                         W I T N E S S E T H  T H A T
                         -------------------- -------

     1.   This Agreement is made pursuant to Section 3.1 of that certain Lease
dated _____________, ___, 19 ___ between Landlord and Tenant.

     2.   It is hereby stipulated that the Lease Term commenced on __________
____, 1999 (being the "Commencement Date" under the Lease); the Rent
Commencement Date with respect to Building __ occurred on _________ ; and the
Expiration Date of the Lease Term shall occur on __________, 20__, unless sooner
extended or terminated, as provided for in the Lease.

     WITNESS the execution hereof under seal by persons hereunto duly
authorized, the date first above written.

                                        LANDLORD:
                                        Boston Properties Limited Partnership,
                                        a Delaware limited partnership

                                             By:  Boston Properties, Inc.,
                                                  a Delaware corporation
                                             Its: General Partner

                                                    ________________________
                                             Name:  ________________________
                                             Its:   ________________________
                                                    Hereunto duly authorized

                                        TENANT:
                                        Parametric Technology Corporation

                                        By: ________________________
                                             Name:  ________________________
                                             Its:   ________________________
                                                    Hereunto duly authorized

                              EXHIBIT E -- Page 1
<PAGE>

                                   EXHIBIT F
                                   ---------

                             INTENTIONALLY OMITTED
                             ---------------------

                              EXHIBIT F -- Page 1
<PAGE>

                                   EXHIBIT G
                                   ---------

              BROKER DETERMINATION OF PREVAILING FAIR MARKET RENT
              ---------------------------------------------------

Definition of Prevailing Fair Market Rent:

"Prevailing Fair Market Rent" shall be defined as of the date in question as the
rent for the Premises in its "as-is" condition to third parties who are not then
occupying the Premises, When making such determination, reference is made to
lease transactions for comparable space in comparable buildings in the Route 128
area from Needham to Waltham ("Market Area"). Appropriate adjustments shall be
made to the rental rates for such transactions to take into account all relevant
factors, including without limitation, any economic concessions then being
granted by landlords to tenants.

Notwithstanding any implication to the contrary in the Lease contained, Landlord
shall have no obligation to make any additional payment to Tenant in respect of
any construction allowance or the like or to perform any work to the Premises as
a result of the exercise by Tenant of any extension option under the Lease;
however, if Landlord does not elect to provide such allowance or to perform any
work, the Prevailing Fair Market Rent shall nevertheless, as provided above,
take into account whether construction allowances are granted by landlords and
whether work is being performed by landlords for the benefit of tenants.

Broker Determination Process:

     Where in the Lease to which this Exhibit is attached provision is made for
a Broker Determination of Prevailing Fair Market Rent, the following procedures
and requirements shall apply:

1.   Request. Tenant or Landlord (the "Requesting Party") shall send a notice to
     -------
     the other party in accordance with the applicable provision of the Lease,
     requesting a Broker Determination of the Prevailing Fair Market Rent, which
     notice to be effective must (i) make explicit reference to the Lease and to
     the specific section of the Lease pursuant to which said request is being
     made, (ii) include the name of a broker selected by the Requesting Party to
     act for the Requesting Party, which broker shall be affiliated with a major
     Boston commercial real estate brokerage firm selected by the Requesting
     Party and which broker shall have at least ten (10) years experience
     dealing in properties of a nature and type generally similar to the
     Property located in the Market Area, and (iii) explicitly state that the
     other party ("Responding Party") is required to notify the Requesting Party
     within twenty (20) days of an additional broker selected by the Responding
     Party.

2.   Response. Within twenty (20) days after the Responding Party's receipt of
     --------
     the Requesting Party's notice requesting the Broker Determination and
     stating the name of the broker selected by the Requesting Party, the
     Responding Party shall

                              EXHIBIT G -- Page 1
<PAGE>

     give written notice to the Requesting Party of the Responding Party's
     selection of a broker having at least the affiliation and experience
     referred to above.

3.   Selection of Third Broker. Within ten (10) days thereafter the two (2)
     -------------------------
     brokers so selected shall select a third such broker also having at least
     the affiliation and experience referred to above.

4.   Rental Value Determination. Within thirty (30) days after the selection of
     --------------------------
     the third broker, the three (3) brokers so selected, by majority opinion,
     shall make a determination of the Prevailing Fair Market Rent. The brokers
     shall advise Landlord and Tenant in writing by the expiration of said
     thirty (30) day period of their determination of the applicable Prevailing
     Fair Market Rent ("Broker Determination").

5.   Resolution of Broker Deadlock. If the Brokers are unable to agree at least
     -----------------------------
     by majority on a determination of Prevailing Fair Market Rent, then the
     brokers shall send a notice to Landlord and Tenant by the end of the thirty
     (30) day period for making said determination setting forth their
     individual determinations of Prevailing Fair Market Rent, and the highest
     such determination and the lowest such determination shall be disregarded
     and the remaining determination shall be deemed to be the Prevailing Fair
     Market Rent.

6.   Costs. Each party shall pay the costs and expenses of the broker selected
     -----
     by it and each shall pay one half (1/2) of the costs and expenses of the
     third broker.

7.   Failure to Select Broker or Failure of Broker to Serve. If the Requesting
     ------------------------------------------------------
     Party shall have requested a Broker Determination and the Responding Party
     shall not have designated a broker within the time period provided therefor
     above and such failure shall continue for more than ten (10) days after
     notice thereof, then the Requesting Party's broker shall alone make the
     determination of the Prevailing Fair Market Rent in writing to Landlord and
     Tenant within thirty (30) days after the expiration of the Responding
     Party's right to designate a broker hereunder. If Tenant and Landlord have
     both designated brokers but the two brokers so designated do not, within a
     period of fifteen (15) days after the appointment of the second broker,
     agree upon and designate the third broker willing so to act, the Tenant,
     the Landlord or either broker previously designated may request the Greater
     Boston Real Estate Board, Inc. to designate the third broker willing so to
     act and a broker so appointed shall, for all purposes, have the same
     standing and powers as though he had been seasonably appointed by the
     brokers first appointed. In case of the inability or refusal to serve of
     any person designated as a broker, or in case any broker for any reason
     ceases to be such, a broker to fill such vacancy shall be appointed by the
     Tenant, the Landlord, the brokers first appointed or the said Greater
     Boston Real Estate Board, Inc., as the case may be, whichever made the
     original appointment, or if the person who made the original appointment
     fails to fill such vacancy, upon application of any broker who

                              EXHIBIT G -- Page 2
<PAGE>

     continues to act or by the Landlord or Tenant such vacancy may be filled by
     the said Greater Boston Real Estate Board, Inc., and any broker so
     appointed to fill such vacancy shall have the same standing and powers as
     though originally appointed.

                              EXHIBIT G --Page 3
<PAGE>

                                  EXHIBIT H-1
                                  -----------
                                FORM OF GENERAL
                                ---------------
                               LETTER OF CREDIT
                               ----------------

BENEFICIARY:                                      ISSUANCE DATE:

                                                  ________________, 199__

[Landlord's Name]
c/o ______________________                        IRREVOCABLE STANDBY
                                                  LETTER OF CREDIT NO.

ACCOUNTEE/APPLICANT:                              MAXIMUM/AGGREGATE
                                                  CREDIT AMOUNT:______
_________________                                 USD ______________
[TENANT NAME]

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
____________________ US Dollars ($___________) 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 the Lease (the
"Lease") dated _____________________ by and between Boston Properties Limited
Partnership, as Landlord, and Parametric Technology Corporation, 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 ______________, 200_
(the "Stated Expiration Date"). It is a condition of this Letter of Credit that
the Stated
                             EXHIBIT H-1 -- Page 1
<PAGE>

Expiration Date shall be deemed automatically extended without amendment for
successive one (1) year periods from such Stated Expiration Date, unless at
least forty-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.

                             EXHIBIT H-1 -- Page 2
<PAGE>

                                  EXHIBIT H-2
                                  -----------
                          FORM OF TI LETTER OF CREDIT
                          ---------------------------

BENEFICIARY:                                      ISSUANCE DATE:
                                                  ________________, 199__

[Landlord's Name]
c/o _____________________                         IRREVOCABLE STANDBY
                                                  LETTER OF CREDIT NO.

ACCOUNTEE/APPLICANT:                              MAXIMUM/AGGREGATE
                                                  CREDIT AMOUNT:______
_________________                                 USD ______________
[TENANT NAME]

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
____________________ US Dollars ($___________) 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 the Lease (the
"Lease") dated _________________ by and between Boston Properties Limited
Partnership, as Landlord, and Parametric Technology Corporation, 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 ________________, 200_
(the "Stated Expiration Date").

                             EXHIBIT H-2 --Page 1

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