Document:

<PAGE>
                                                                    Exhibit 10.5

THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED,
OR APPLICABLE STATE SECURITIES LAWS.  THIS NOTE MAY NOT BE SOLD, OFFERED FOR
SALE, PLEDGED OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION
STATEMENT AS TO THIS NOTE UNDER SAID ACT AND APPLICABLE STATE SECURITIES LAWS.

                         FULL RECORSE PROMISSORY NOTE

$200,000.00                                                      August 31, 1999

     FOR VALUE RECEIVED, Ming Tsai, who resides at 46 Hampshire Road, Wellesley,
MA, ("Borrower") promises to pay to the order of Mainspring Communications, Inc.
      --------
("Lender"), the principal sum of Two Hundred Thousand Dollars ($200,000.00) plus
  ------
interest in arrears from and including the date hereof on the principal balance
from time to time outstanding, computed daily, at a rate per annum of 8.0%.

     Borrower agrees to make principal and interest payments on this Note as
described in Exhibit A.  In the event Borrower leaves the employment of Lender
             ---------
prior to the repayment in full of this Note, Borrower shall have thirty days
from the date of termination to repay the remaining principal balance of the
Note plus accrued and unpaid interest.

     Lender shall have full recourse against Borrower personally for collection
and payment of the debt evidenced by this Note.

     No delay or omission on the part of Lender in exercising any right
hereunder shall operate as a waiver of such right or of any other right of
Lender, nor shall any delay, omission or waiver on any one occasion be deemed a
bar to or waiver of the same or any other right on any future occasion.

     This Note may be prepaid at any time, in whole or in part, by Borrower
without premium or penalty.

     Borrower hereby waives presentment, demand, protest, and notice of every
kind.  Borrower shall pay on demand all costs, including court costs and
reasonable attorneys' fees, paid or incurred by Lender in enforcing this Note
upon default.

     This Note shall be governed by and construed in accordance with the laws of
the Commonwealth of Massachusetts.

                                  Page 1 of 3
<PAGE>

     IN WITNESS WHEREOF, the parties have caused this Note to be signed under
seal, as of the date first above written.

                                    BORROWER:

                                     /s/ Ming Tsai
                                    -----------------------------------
                                    Ming Tsai

                                    LENDER:

                                    Mainspring Communications, Inc.

                                    By: /s/ Mark A. Verdi
                                       --------------------------------
                                       Mark A. Verdi
                                       Sr. Vice President, Finance and
                                       Operations

                                  Page 2 of 3
<PAGE>

                                                                       Exhibit A
                                                                       ---------

                              Repayment Schedule

1.  Upon completion of one full year of continuous employment with Mainspring,
    Mainspring will forgive One Hundred Thousand Dollars ($100,000) of the
    principal amount of this note ("Forgiven Balance"), plus all accrued
    interest related to the Forgiven Balance.

2.  The remaining principal balance of One Hundred Thousand Dollars ($100,000)
    plus all accrued interest from the date of this Note will be due and payable
    on August 31, 2001 (two years from the date of this Note).

                                  Page 3 of 3<PAGE>
                                                                    Exhibit 10.6

                                     LEASE

                                    BETWEEN

           RIVERFRONT OFFICE PARK ASSOCIATES II LIMITED PARTNERSHIP

                                   Landlord

                                      AND

                        MAINSPRING COMMUNICATIONS, INC.

                                    Tenant

                               ONE MAIN STREET,
                           CAMBRIDGE, MASSACHUSETTS
<PAGE>

                                     INDEX
                                     -----

<TABLE>
<CAPTION>
<S>                                                                            <C>
1.   REFERENCE DATA.........................................................    1

2.   DESCRIPTION OF DEMISED PREMISES........................................    2

   2.1    Demised Premises..................................................    2
   2.2    Appurtenant Rights................................................    2
   2.3    Reservations......................................................    3

3.   TERM OF LEASE; OPTION TO EXTEND TERM; RIGHT OF FIRST OFFER.............    3

   3.1    Habendum..........................................................    3
   3.2    Term Commencement Date............................................    3
   3.3    Option to Extend..................................................    3
   3.4    Right of First Offer..............................................    4

4.   WORK BY LANDLORD; TENANT'S ACCESS......................................    4

   4.1    Completion Date - Delays..........................................    4
   4.2    When Premises Deemed Ready........................................    4
   4.3    Change Orders, Tenant's Delays....................................    4
   4.4    Conclusiveness of Landlord's Performance..........................    5
   4.5    Entry by Tenant: Interference with Construction...................    5

5.   USE OF PREMISES........................................................    5

   5.1    Permitted Use.....................................................    5
   5.2    Prohibited Uses...................................................    5
   5.3    Licenses and Permits..............................................    6

6.   RENT...................................................................    6

   6.1    Yearly Fixed Rent.................................................    6
   6.2    Taxes.............................................................    6
   6.3    Operating Expenses................................................    7
   6.4    Tenant's Proportionate Share......................................    8
   6.5    Payment to Mortgagee..............................................    8

7.   UTILITIES AND LANDLORD'S SERVICES......................................    8

   7.1    Electricity.......................................................    8
   7.2    Water Charges.....................................................    9
   7.3    Heat and Air Conditioning.........................................    9
   7.4    Additional Heat, Cleaning and Air Conditioning Services...........    9
   7.5    Repairs and Other Services........................................   10
   7.6    Interruption or Curtailment of Services...........................   10

8.   CHANGES OR ALTERATIONS BY LANDLORD.....................................   10

9.   FIXTURES, EQUIPMENT AND IMPROVEMENTS - REMOVAL BY TENANT...............   11
</TABLE>
<PAGE>

<TABLE>
<S>                                                                                               <C>
10.  ALTERATIONS AND IMPROVEMENTS BY TENANT....................................................   11

11.  TENANT'S CONTRACTORS - MECHANICS' AND OTHER LIENS - STANDARD OF
TENANT'S PERFORMANCE - COMPLIANCE WITH LAWS....................................................   11

12.  REPAIRS AND SECURITY BY TENANT............................................................   12

13.  INSURANCE.  INDEMNIFICATION, EXONERATION AND EXCULPATION..................................   13

   13.1   Insurance............................................................................   13
   13.2   Certificates of Insurance............................................................   13
   13.3   General..............................................................................   14
   13.4   Property of Tenant...................................................................   14
   13.5   Bursting of Pipes, etc...............................................................   14
   13.6   Repairs and Alterations - No Diminution of Rental Value..............................   15

14.  ASSIGNMENT, MORTGAGING, SUBLETTING, ETC...................................................   15

   14.1   Restrictions.........................................................................   15
   14.2   Requests to Assign or Sublet.........................................................   15
   14.3   Exceptions...........................................................................   16
   14.4   Excess Rent..........................................................................   16
   14.5   Recapture............................................................................   16
   14.6   Further Documentation................................................................   18
   14.7   General..............................................................................   18

15.  MISCELLANEOUS COVENANTS...................................................................   19

   15.1   Rules and Regulations................................................................   19
   15.2   Access to Premises - Shoring.........................................................   19
   15.3   Accidents to Sanitary and Other Systems..............................................   20
   15.4   Signs, Blinds and Drapes.............................................................   20
   15.5   Estoppel Certificate.................................................................   21
   15.6   Prohibited Items.....................................................................   21
   15.7   Requirements of Law; Fines and Penalties.............................................   21
   15.8   Tenant's Acts - Effect on Insurance..................................................   21
   15.9   Hazardous Materials..................................................................   22
   15.10  Miscellaneous........................................................................   22

16.  DAMAGE BY FIRE, ETC.......................................................................   22

17.  WAIVER OF SUBROGATION.....................................................................   24

18.  CONDEMNATION - EMINENT DOMAIN.............................................................   25

19.  DEFAULT...................................................................................   26

   19.1   Conditions of Limitation - Re-entry - Termination....................................   26
   19.2   Damages - Assignment for Benefit of Creditors........................................   26
   19.3   Damages - Termination................................................................   27
</TABLE>
<PAGE>

<TABLE>
<S>                                                                                       <C>
   19.4   Fees and Expenses............................................................   28
   19.5   Landlord's Remedies Not Exclusive............................................   28
   19.6   Grace Period.................................................................   28

20.  END OF TERM - ABANDONED PROPERTY..................................................   29

21.  RIGHTS OF MORTGAGEES..............................................................   29

   21.1   Superiority of Lease.........................................................   29
   21.2   Entry and Possession.........................................................   30
   21.3   Right to Cure................................................................   30
   21.4   Duty to Construct............................................................   30
   21.5   Prepaid Rent.................................................................   31
   21.6   Continuing Offer.............................................................   31
   21.7   Subordination................................................................   31
   21.8   Limitations on Liability.....................................................   31

22.  QUIET ENJOYMENT...................................................................   32

23.  ENTIRE AGREEMENT - WAIVER - SURRENDER.............................................   32

   23.1   Entire Agreement.............................................................   32
   23.2   Waiver by Landlord...........................................................   32
   23.3   Surrender....................................................................   33

24.  INABILITY TO PERFORM - EXCULPATORY CLAUSE.........................................   33

25.  BILLS AND NOTICES.................................................................   33

26.  PARTIES BOUND - SEIZING OF TITLE..................................................   34

27.  MISCELLANEOUS.....................................................................   34

   27.1   Separability.................................................................   35
   27.2   Captions.....................................................................   35
   27.3   Broker.......................................................................   35
   27.4   Governing, Law...............................................................   35
   27.5   Assignment of Rents..........................................................   35
   27.6   Parking......................................................................   35
   27.7   Notice of Lease..............................................................   36
   27.8   Financial Statements.........................................................   36
</TABLE>

EXHIBIT A   Description of Demised Premises
EXHIBIT B   Description of Land
EXHIBIT C   Approved Plan
EXHIBIT D   Procedure for Allocation of Costs of Electric Power Usage by Tenants
EXHIBIT E   Rules and Regulations
<PAGE>

                              AGREEMENT OF LEASE

          AGREEMENT OF LEASE made as of the 31st day of July, 1996, by and
between RIVERFRONT OFFICE PARK ASSOCIATES II LIMITED PARTNERSHIP, a
Massachusetts limited partnership (hereinafter referred to as "Landlord") and
MAINSPRING COMMUNICATIONS, INC., a Delaware corporation (hereinafter referred to
as "Tenant").

                             W I T N E S S E T H:

          Landlord hereby leases to Tenant and Tenant hereby hires from Landlord
that portion of the seventh (7th) floor, as shown on the plan attached hereto as
Exhibit A and made a part hereof (hereinafter referred to as the "Premises" or
---------
the "Demised Premises") contained in the building, known and numbered as One
Main Street, Cambridge, Massachusetts (hereinafter referred to as the
"Building").

1.   REFERENCE DATA

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

(1)  Additional Rent:       Sums or other charges payable by Tenant to Landlord
                            under this Lease, other than Yearly Fixed Rent.

(2)  Broker:                Lynch Murphy Walsh & Partners

(3)  Business Day:          All days except Saturdays, Sundays, and days
                            defined as "Legal Holidays" for the entire state
                            under the laws of the Commonwealth of Massachusetts.

(4)  Land:                  The parcel of land described on Exhibit B attached
                            hereto and made a part hereof.

(5)  Landlord's Address:    c/o Codman Management Company, Inc., One Main
                            Street, Cambridge, Massachusetts 02142.

(6)  Landlord's Architect:  Bryer Architects

(7)  Mortgage:              A mortgage, deed of trust, trust indenture, or other
                            security instrument of record creating an interest
                            in or affecting title to the Land or Building or any
                            part thereof, including the leasehold mortgage, and
                            any and all renewals, modifications, consolidations
                            or extensions of any such instrument. For such time
                            as Teachers Insurance and Annuity Association
                            ("TIAA") is the holder of a first
<PAGE>

                            mortgage on the Property, the term "Mortgage" shall
                            mean only said first mortgage, and such other
                            mortgages, if any, which TIAA shall approve.

(8)  Mortgagee:             The holder of any Mortgage.

(9)  Parking Spaces:        Seven (7).

(10) Property:              The Land and Building.

(11) Rent:                  Yearly Fixed Rent and Additional Rent.

(12) Rentable Area of the
     Demised Premises:      7,069 square feet.

(13) Tenant's Address:      Until the Term Commencement Date One Kendall Square,
                            Cambridge, Massachusetts 02142, and thereafter One
                            Main Street, Cambridge, Massachusetts 02142.

(14) Term Commencement
     Date:                  As defined in Section 3.2.

(15) Term of This Lease:    As defined in Section 3.1.

(16) Termination Date:      As defined in Section 3.1.

(17) Use of Demised
     Premises:              General office purposes.

(18) Yearly Fixed Rent:     $180,047.43 ($25.47 per rentable square foot per
                            annum).

2.   DESCRIPTION OF DEMISED PREMISES

     2.1  Demised Premises.  The Demised Premises are that portion of the
          ----------------
Building as described above (as the same may from time to time be constituted
after changes therein, additions thereto; and eliminations therefrom pursuant
hereto).

     2.2  Appurtenant Rights.  Tenant shall have, as appurtenant to the
          ------------------
Demised Premises, rights to use in common, subject to reasonable rules from time
to time made by Landlord of which Tenant is given notice, those common roadways,
walkways, elevators, hallways and stairways necessary for access to that portion
of the Building occupied by the Demised Premises.

     2.3  Reservations.  All the perimeter walls of the Demised Premises
          ------------
except the inner surfaces thereof, any balconies, terraces or roofs adjacent to
the Demised Premises, and any space in or adjacent to the Demised Premises used
for shafts. stacks, pipes, conduits, wires and appurtenant fixtures, fan rooms,
ducts, electric or other utilities, sinks or other building facilities,
<PAGE>

and the use thereof, as well as the right of access through the Demised Premises
for the purpose of operation, maintenance, decoration and repair as hereinafter
provided. are expressly reserved to Landlord.

3.   TERM OF LEASE; OPTION TO EXTEND TERM; RIGHT OF FIRST OFFER

     3.1  Habendum.  TO HAVE AND TO HOLD the Demised Premises for a term of
          --------
five (5) years commencing on the Term Commencement Date and ending on the day
immediately prior to the fifth (5th) anniversary thereof (the "Term of this
Lease"), or on such earlier date upon which said Term may expire or be
terminated pursuant to any of the conditions of limitation or other provisions
of this Lease or pursuant to law (which date for the termination of the term
hereof shall hereafter be called the "Termination Date").

     3.2  Term Commencement Date.  The Term Commencement Date shall be later
          ----------------------
of (i) August 1, 1996, and (ii) upon substantial completion of the fit-up work
to be done by Landlord pursuant to Section 4.1 hereof.

     3.3  Option to Extend.  Provided Tenant is not then in default of its
          ----------------
obligations under this Lease beyond any applicable grace periods, Tenant may
extend the Term of this Lease for one (1) additional five (5) year period by
giving notice to Landlord of its election to extend at least nine (9) months
prior to the end of the original Term.  The Yearly Fixed Rent payable by Tenant
with respect to such extension period shall be equal to ninety-five percent
(95%) of the then fair market rental value of the Demised Premises (taking into
account comparable first-class office space in the East Cambridge area) (1) as
the same may be mutually agreed by Landlord and Tenant:  provided, however that
(2) if they have not so agreed in writing within two (2) months following the
exercise of the option then said fair market value shall be determined by
appraisers, one to be chosen by Landlord. one to be chosen by Tenant, and a
third to be selected by the two first chosen.  The unanimous written decision of
the two first chosen, without selection and participation of a third appraiser,
or otherwise the written decision of a majority of three appraisers chosen and
selected as aforesaid, shall be conclusive and binding upon Landlord and Tenant.
Landlord and Tenant shall each notify the other of its chosen appraiser within
thirty (30) days following expiration of the aforesaid two (2) month period and,
unless such two appraisers shall have reached a unanimous decision within
seventy-five (75) days from said expiration, they shall within a further fifteen
(15) days elect a third appraiser and notify Landlord and Tenant thereof.
Landlord and Tenant shall each bear the expense of the appraiser chosen by it
and shall equally bear the expense of the third appraiser (if any).

     3.4  Right of First Offer.  In the event that at any time during the Term
          --------------------
of this Lease any rentable spice on the seventh (7th) floor of the Building
becomes or is to become available for rental and Landlord wishes to lease such
space to any person other than the then current occupant thereof (if any), and
in the further event that any existing tenant(s) of the Building who have
heretofore been granted any right(s) of first offer by Landlord with respect to
such space shall fail to exercise such right(s), and in the further event Tenant
is not then in default of its material obligations to Landlord under this Lease.
Landlord shall make a written offer to lease the same to Tenant, stating the
Rent that Landlord will accept and all other material terms and
<PAGE>

conditions of the proposed lease, and Tenant shall have a right of first refusal
to lease such space by giving notice to Landlord to such effect within fifteen
(15) Business Days after notice of such offer. If such notice of acceptance by
Tenant is not so given, then Landlord shall be free to lease such space to a
third party. In any case in which Tenant shall have waived said right of first
refusal, or Tenant shall have failed to timely exercise such right, then Tenant
shall, on request of Landlord, execute and deliver in recordable form an
instrument indicating such waiver or expiration, which instrument shall be
conclusive in favor of all persons relying thereon in good faith.

4.   WORK BY LANDLORD; TENANT'S ACCESS

     4.1  Completion Date - Delays.  Subject to delay by causes beyond the
          ------------------------
reasonable control of Landlord or caused by the action or inaction of Tenant,
Landlord shall use reasonable diligence in order to have the Demised Premises
ready for occupancy by Tenant by August 16, 1996, in accordance with the plans
dated July 1, 1996 prepared by Landlord's Architect attached hereto as Exhibit C
                                                                       ---------
and made a part hereof (the "Approved Plans").  The failure to have the Demised
Premises so ready by such date shall in no way affect the validity of this Lease
or the obligations of Tenant hereunder.

     4.2  When Premises Deemed Ready.  The Demised Premises shall be
          --------------------------
conclusively deemed ready for Tenant's occupancy after Landlord gives notice to
Tenant that the fit-up work to be done by Landlord in the Demised Premises
pursuant to the Approved Plans have been substantially completed by Landlord
insofar as is practicable in view of delays or defaults, if any, of Tenant.
Such work shall not be deemed incomplete if only minor or insubstantial details
of construction or mechanical adjustments remain to be done, or if a delay is
caused in whole or in part by Tenant through the delay of Tenant in submitting
any plans, and/or specifications. supplying information, approving plans,
specifications or estimates, giving authorization or otherwise.  Landlord's
Architect's certificate of substantial completion as hereinabove stated, given
in good faith, or of any other facts pertinent to this Section 4.2 shall be
deemed conclusive of the statements therein contained and binding upon Tenant.

     4.3  Change Orders, Tenant's Delays.  In the event of (a) any change
          ------------------------------
orders to the Approved Plans requested by Tenant and consented to by Landlord,
or (b) any delay ("Tenant's Delay") that shall occur in the Term Commencement
Date as a result of

          (i)  any request by Tenant that Landlord delay completion of any fit-
up work with respect to the Demised Premises for any reason; or

          (ii) to timely execute a work letter if requested by Landlord; or

          (iii)any necessary rescheduling of the sequence of any fit-up work
with respect to the Demised Premises due to any of the causes listed above;

which results in any additional cost to Landlord (the excess of what would have
been Landlord's total cost of completing the fit-up work for the Demised
Premises had there not occurred such
<PAGE>

change order or delay), Tenant agrees to promptly pay to Landlord, whether or
not the Term of this Lease has commenced, the full amount of such additional
cost.

     4.4  Conclusiveness of Landlord's Performance.  Tenant shall be
          ----------------------------------------
conclusively deemed to have agreed that Landlord has performed all of its
obligations under this Article 4 unless not later than sixty (60) days after the
Term Commencement Date Tenant shall give Landlord written notice specifying the
respects in which Landlord has not performed such obligations.

     4.5  Entry by Tenant: Interference with Construction.  In the event that
          -----------------------------------------------
Tenant is permitted by Landlord to enter the Demised Premises prior to the Term
Commencement Date to undertake such work as is to be performed by Tenant
pursuant to this Lease in order to prepare the Demised Premises for Tenant's
occupancy, such entry shall be deemed to be pursuant to a license from Landlord
to Tenant and shall be at the risk of Tenant.  In no event shall Tenant
interfere with any construction work being performed by or on behalf of Landlord
in or around the Building; without limiting the generality of the foregoing,
Tenant shall comply with all instructions issued by Landlord's contractors
relative to the moving of Tenant's equipment and other property into the Demised
Premises -and shall pay any fees or costs imposed in connection therewith.

5.   USE OF PREMISES

     5.1  Permitted Use.  Except as otherwise agreed by Landlord, Tenant.
          -------------
during the Term of this Lease. shall occupy and use the Demised Premises for the
Permitted Use set forth in Article I and for no other purpose.  Service and
utility areas (whether or not a part of the Premises) shall he used only for the
particular purpose for which they are designated.

     5.2  Prohibited Uses.  Tenant shall not use, or suffer or permit the use
          ---------------
of. or suffer or permit anything to be done in or anything to be brought into or
kept in, the Demised Premises or any part thereof (i) which would violate any of
the covenants, agreements, terms, provisions and conditions of this Lease, (ii)
for any unlawful purposes or in any unlawful manner. or (iii) which, in the
reasonable judgment of Landlord shall in any way (a) impair or tend to impair
the appearance or reputation of the Building, (b) impair or interfere with or
tend to impair or interfere with any of the Building services or the proper and
economic heating, cleaning, air conditioning or other servicing of the Building
or Demised Premises, or with the use of any of the other areas of the Building,
or (c) occasion discomfort, inconvenience or annoyance to any of the other
tenants or occupants of the Building, whether through the transmission of noise
or odors or otherwise.  Without limiting the generality of the foregoing, no
food shall be prepared or served for consumption on or about the Demised
Premises; no intoxicating liquors or alcoholic beverages shall be sold on or
about the Demised Premises; no lottery tickets (even where the sale of such
tickets is not illegal) shall be sold and no gambling, betting or wagering shall
otherwise be permitted oil or about the Demised Premises; no loitering shall be
permitted in or about the Demised Premises; and no loading or unloading of
supplies or other material to or from the Demised Premises shall be permitted on
the Land except at times and in locations to be designated by Landlord.  The
Demised Premises shall be maintained in a sanitary condition, and
<PAGE>

all kept free of rodents and vermin. All trash and rubbish shall be suitably
stored in the Demised Premises or other locations designated by Landlord from
time to time.

     5.3  Licenses and Permits.  If any governmental license or permit shall
          --------------------
be required for the proper and lawful conduct of Tenant's business, and if the
failure to secure such license or would in any way affect Landlord, Tenant, at
Tenant's expense, shall duly procure and thereafter maintain such license or
permit and submit the same to inspection by Landlord.  Tenant, at Tenant's
expense, shall at all times comply with the terms and conditions of each such
license or permit.

6.   RENT

     6.1  Yearly Fixed Rent.  Tenant shall pay to Landlord, without any set-
          -----------------
off or deduction, it Landlord's office, or to such other person or at such other
place as Landlord may designate by notice to Tenant, the Yearly Fixed Rent set
forth in Article 1. All Yearly Fixed Refit shall be paid in equal monthly
installments in advance on or before the first business day of each calendar
month during the Term of this Lease and shall be apportioned for any fraction of
a month in which the Term Commencement Date or the last day of the Term of this
Lease may fall.

     6.2  Taxes.  Tenant shall pay to Landlord as Additional Rent a
          -----
proportionate share (as defined in Section 6.4) of all real estate taxes
(including without limitation all betterment assessments and charges in lieu of
such taxes and any tax on any fixture (other than a Tenant fixture) installed in
the Building, even if taxed as personal property) imposed against the Building
and the Land in any fiscal tax year, in excess of the amount of said real estate
taxes imposed against the Building and the Land for the fiscal tax year ending
June 30, 1997, prorated with respect to any portion of a fiscal year in which
the term of this Lease begins or ends.  Such payments shall be due and payable
within thirty (30) days after Tenant shall have received a copy of the relevant
tax bills.  If Landlord shall receive any refund of real estate taxes of which
Tenant has paid a portion pursuant to this Section, then, out of any balance
remaining after deducting Landlord's expenses incurred in obtaining such refund,
Landlord shall pay to Tenant the same proportionate share of said balance,
prorated as set forth above.  Tenant shall, if, as and when demanded by Landlord
and with each monthly installment of Fixed Rent, make tax fund payments to
Landlord.  "Tax Fund Payments" refer to such payments as Landlord shall
determine to be sufficient to provide in the aggregate a fund adequate to pay,
when they become due and payable, all payments required from Tenant under this
Section.  In the event that said tax fund payments are not adequate to pay
Tenant's share of such taxes, Tenant shall pay to Landlord the amount by which
such aggregate is less than the amount of said share, such payment to be due and
payable at the time set forth above.  Any surplus tax fund payments shall be
accounted for to Tenant after payment by Landlord of the taxes on account of
which they were made, and shall be promptly refunded to Tenant.

     6.3  Operating Expenses.  Tenant shall pay to Landlord as Additional Rent
          ------------------
a proportionate share (as defined in Section 6.4) of all costs and expenses
incurred by Landlord in the operation and maintenance of the Building and the
Land in accordance with generally accepted operational and maintenance
procedures in any calendar year, in excess of the amount
<PAGE>

of said costs and expenses incurred by the Landlord in the operation and
maintenance of the Building and the Land during the calendar year ending
December 31, 1996, including. without limiting the generality of the foregoing,
all such costs and expenses in connection with (1) insurance, license fees,
janitorial service, landscaping, and snow removal, (2) wages. salaries,
management fees, employee benefits, payroll taxes, on-site office expenses,
administrative and auditing expenses, and equipment and materials for the
operation, management, and maintenance of said Property, (3) any capital
expenditure (amortized, with interest, on such reasonable basis as Landlord
shall determine) made by Landlord for the purpose of reducing other operating
expenses or complying with any government requirement, (4) the furnishing of
heat, air conditioning, utilities. and any other service to the common areas of
the Building (i.e., areas not constituting a part of the demised premises of any
tenant in the Building), (5) the operation and servicing of any computer system
installed to regulate Building equipment, and (6) the furnishing of the repairs
and services referred to in Section 7.3 (the foregoing being hereinafter
referred to as "operating expenses"). As soon as Tenant's share of operating
expenses with respect to any calendar year can be determined, the same will be
certified by Landlord to Tenant and will become payable to Landlord within
thirty (30) days following such certification, subject to proration with respect
to any portion of a calendar year in which the Term of this Lease begins or
ends. Tenant shall, if, as and when demanded by Landlord and with each monthly
installment of Yearly Fixed Rent, make operating fund payments to Landlord.
"Operating Fund Payments" refer to such payments as Landlord shall reasonable
determine to be sufficient to provide in the aggregate a fund adequate to pay,
when they become due and payable, all payments required from Tenant under this
Section. In the event that operating fund payments are so demanded, and if the
aggregate of said operating fund payments is not adequate to pay Tenant's share
of operating expenses, Tenant shall pay to Landlord the amount by which such
aggregate is less than the amount of said share, such payment to be due and
payable at the time set forth above. Any surplus operating fund payments shall
be accounted for to Tenant after such surplus has been determined, and shall be
refunded to Tenant promptly.

      6.4  Tenant's Proportionate Share.  Tenant's proportionate share of
           ----------------------------
 taxes pursuant to Section 6.2 and operating expenses pursuant to Section 6.3,
 respectively, shall be 2.17% (7,069 square feet divided by 326,470 square feet)
 and 2.20% (7,069 square feet divided by 321,917 square feet), respectively.

      6.5  Payment to Mortgagee.  Landlord reserves the right to provide in
           --------------------
 any Mortgage given by it of the Property that some or all rents, issues, and
 profits and all other amounts of every kind payable to (the Landlord under this
 Lease shall be paid directly to the Mortgagee for Landlord's account and Tenant
 covenants and agrees that it will, after receipt by it of notice from Landlord
 or Mortgagee designating such Mortgagee to whom payments are to be made by
 Tenant, pay such amounts thereafter becoming due directly to such Mortgagee
 until excused therefrom by notice from such Mortgagee.

7.   UTILITIES AND LANDLORD'S SERVICES

     7.1  Electricity.  Tenant shall pay to Landlord monthly an amount
          -----------
reasonably estimated by Landlord to equal Tenant's Allocable Electricity Costs
for the electrical energy that Tenant
<PAGE>

requires for operation of the lighting fixtures, appliances and equipment of
Tenant in the Demised Premises and the heating and air conditioning equipment of
Landlord servicing the Demised Premises. "Tenant's Allocable Electricity Costs"
as used herein shall be as determined in accordance with Exhibit D annexed
                                                         ---------
hereto and made a part hereof. Landlord shall furnish to Tenant quarterly a
statement setting forth in reasonable detail the particulars relating to
Tenant's Allocable Electricity Costs for the three months to which such a
statement relates. In the event the estimated payments made by Tenant for said
three (3) month period shall be less than Tenant's Allocable Electricity Costs
for said period as set forth in said statement, Tenant shall promptly remit to
Landlord the difference. In the event the estimated payments made by Tenant for
said three (3) month period exceed Tenant's Allocable Electricity Costs for said
period as set forth in said statement, such excess shall be refunded by
Landlord. Landlord shall not be liable in any way to Tenant for any failure or
defect in the supply or character of electrical energy furnished to the Demised
Premises by reason of any requirement, act or omission of the public utility
serving the Building with electricity unless due to the act or omission of
Landlord. Tenant's use of electrical energy in the Demised Premises shall not at
any time exceed the capacity of any of the electrical conductors and equipment
in or otherwise serving the Demised Premises. In order to insure that such
capacity is not exceeded and to avert possible adverse affect upon the Building
electrical services, Tenant shall give notice to Landlord and obtain Landlord's
prior written consent whenever Tenant shall connect to the Building electrical
distribution system any fixtures, appliances or equipment. Any additional
feeders or risers to supply Tenant's electrical requirements in addition to
those originally installed and all other equipment proper and necessary in
connection with such feeders or risers, shall be installed by Landlord upon
Tenant's request, at the sole cost and expense of Tenant, provided that such
additional feeders and risers are permissible under applicable laws and
insurance regulations and the installation of such feeders or risers will not
cause permanent damage or injury to the Building or cause or create a dangerous
condition or unreasonably interfere with other tenants of the Building. Tenant
agrees that it will not make any 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 alteration or
addition to such electrical equipment and/or appliances. Tenant, at Tenant's
expense, shall purchase, install and replace all light fixtures, bulbs, tubes,
lamps, lenses, globes, ballasts and switches used in the Demised Premises.
Notwithstanding the foregoing, Landlord, at its election, may install at
Landlord's cost and expense a separate meter for Tenant's electric usage in
which event Tenant shall thereafter obtain and pay for its electricity directly
from the electric utility servicing the Building.

     7.2  Water Charges.  Landlord shall furnish hot and cold water for
          -------------
ordinary cleaning, toilet, lavatory and drinking purposes to the extent required
to service facilities shown on the Plans approved by Landlord pursuant to
Section 4.3.  If Tenant requires, uses or consumes water for any purpose other
than for such purposes, Landlord may (i) assess a reasonable charge for the
additional water so used or consumed by Tenant or (ii) install a water meter and
thereby measure Tenant's water consumption for all purposes.  In the latter
event, Landlord shall pay the cost of the meter and the cost of installing any
equipment required in connection therewith, and Tenant shall keep said meter and
installation equipment in good working order and repair, and shall pay for water
consumed, as shown on said meter, together with the sewer charge based on said
meter
<PAGE>

charges, as and when bills are rendered.  On Tenant's default in making
such payment Landlord may pay such charges and collect the same from Tenant.

     7.3  Heat and Air Conditioning.  Landlord shall, through the equipment of
          -------------------------
the Building furnish to and distribute in the Demised Premises heat and air
conditioning as normal seasonal changes may require on Business Days from 8:00
a.m. to 6:00 p.m. and on Saturdays (other than legal or recognized holidays as
defined in Article 1) from 8:00 a.m. to 12:00 noon when reasonably required for
the comfortable occupancy of the Demised Premises by Tenant.  Tenant agrees to
lower and close the blinds or drapes when necessary because of the sun's
position, whenever the air conditioning system is in operation, and to cooperate
fully with Landlord with regard to, and to abide by all the regulations and
requirements which Landlord may prescribe for the proper functioning and
protection of the heating and air conditioning system.

     7.4  Additional Heat, Cleaning and Air Conditioning Services.
          -------------------------------------------------------

          (a)  The heating and air conditioning equipment serving the Demised
Premises shall be designed so as to permit Tenant to obtain heat and air
conditioning on days and at times other than as set forth in Section 7.3.
Tenant's use of such additional heat and air conditioning shall be gauged on the
meter referred to in Section 7.1 or otherwise reasonably estimated by Landlord,
and all cities in connection therewith shall be payable directly by Tenant.

          (b)  Tenant will pay to Landlord a reasonable charge for any extra
cleaning of the Premises required because of the carelessness or indifference of
Tenant or because of the nature of Tenant's business, or furnished by Landlord
at Tenant's request.  Landlord will endeavor to furnish such requested extra
cleaning service upon reasonable advance written notice from Tenant of its
requirements in that regard.

     7.5  Repairs and Other Services.  Except as otherwise provided in
          --------------------------
Articles 16 and 18, and subject to Tenant's obligations in Article 12 and
elsewhere in this Lease, Landlord shall (a) keep and maintain the roof, exterior
walls, structural floor slabs and columns, windows (exclusive of glass
components), and common areas of the Building in as good condition and repair as
they are in on the Term Commencement Date, reasonable use and wear excepted, (b)
keep and maintain in workable condition the Building's sanitary, electrical,
heating, air conditioning and other systems, (c) provide cleaning services to
the Demised Premises and the common areas of the Building on Business Days
according to the cleaning standards generally prevailing in first class office
buildings in the City of Cambridge, (d) provide maintenance and snow removal for
all roadways, walkways and parking areas on the Property, (e) provide grounds
maintenance to all landscaped areas, and (f) employ a uniformed guard to be
stationed at the main entrance of the Building on an around-the-clock basis.
All expenses incurred by Landlord in connection with the foregoing repairs and
other services shall be included as part of operating expenses pursuant to
Section 6.3.

     7.6  Interruption or Curtailment of Services.  Landlord reserves the
          ---------------------------------------
right to interrupt, curtail, stop or suspend the furnishing of services and the
operation of any Building system, when
<PAGE>

necessary by reason of accident or emergency, or of repairs, alterations,
replacements or improvements in the reasonable judgment of Landlord desirable or
necessary to be made, or of difficulty or inability in securing supplies or
labor, or of strikes, or of any other cause beyond the reasonable control of
Landlord, whether such other cause be similar or dissimilar to those hereinabove
specifically mentioned, until said cause has been removed. Landlord shall have
no responsibility or liability for any such interruption, curtailment, stoppage,
or suspension of services or systems, except that Landlord shall exercise
reasonable diligence to minimize inconvenience to Tenant and to eliminate the
cause of same and except that Landlord shall give reasonable notice of such
interruption, curtailment, stoppage or suspension except when due to accident or
emergency.

8.   CHANGES OR ALTERATIONS BY LANDLORD

     Landlord reserves the right, exercisable by itself or its nominee, at any
time and from time to time without the same constituting an actual or
constructive eviction and without incurring any liability to Tenant therefor or
otherwise affecting Tenant's obligations under this Lease, to make such changes,
alterations, additions, improvements, repairs or replacements in or to the
Building (including the Demised Premises) and the fixtures and equipment
thereof, as well as in or to the street entrances, halls, passages, elevators,
and stairways thereof, as it may deem necessary or desirable, and to change the
arrangement and/or location of entrances or passageways, doors and doorways, and
corridors, elevators, stairs, toilets, or other public parts of the Building,
provided, however, that there be no unreasonable obstruction of the right of
access to, or unreasonable interference with the use and enjoyment of, the
Demised Premises by Tenant, except that Landlord shall not be obligated to
employ labor at so-called "overtime" or other premium pay rates.  Nothing
contained in this Article shall be deemed to relieve Tenant of any duty,
obligation or liability of Tenant with respect to making or causing to be made
any repair, replacement or improvement or complying with any law, order or
requirement of any governmental or other authority.  Landlord reserves the right
to from time to time change the address of the Building.  Neither this Lease nor
any use by tenant shall give Tenant any right or easement or the use of any door
or any passage or any concourse connecting with any other building or to any
public convenience, and the use of such doors, passages and concourses and of
such conveniences may be regulated or discontinued at any time and from time to
time by Landlord and without affecting the obligation of Tenant hereunder or
incurring any liability to Tenant therefor.

9.   FIXTURES, EQUIPMENT AND IMPROVEMENTS - REMOVAL BY TENANT

     All fixtures, equipment, improvements and appurtenances attached to or
built into the Demised Premises prior to or during the term, whether by Landlord
at its expense or at the expense of Tenant (either or both) or by Tenant shall
be and remain part of the Demised Premises and shall not be removed by Tenant at
the end of the Term unless otherwise expressly provided in this Lease.  Where
not built into the Demised Premise and if furnished and installed by and at the
sole expense of Tenant, all removable electric fixtures, signs, furniture, or
trade fixtures or business equipment shall not be deemed to be included in such
fixtures, equipment, improvements and appurtenances and may be, and upon the
request of Landlord will be, removed by Tenant upon the condition that such
removal shall not materially damage the Demised
<PAGE>

Premises or the Building and that the cost of repairing any damage to the
Demised Premises or the Building arising from such removal shall be paid by
Tenant.

10.  ALTERATIONS AND IMPROVEMENTS BY TENANT

     Tenant shall make no alterations, installations, removals, additions or
improvements in or to the Demised Premises without Landlord's prior written
consent and then only by contractors or mechanics approved by Landlord.  No
installations or other such work shall be undertaken or begun by Tenant until
Landlord has approved written plans and specifications therefor; and no
amendments or additions to such plans and specifications shall be made without
prior written consent of Landlord, which consent shall not be unreasonably
withheld.  Any such work, alterations, decorations, installations, removals,
additions and improvements shall be done at the sole expense of Tenant and at
such times and in such manner as Landlord may from time to time designate.  If
Tenant shall make any alterations, decorations, installations, additions or
improvements, then Landlord may elect at the time of its consent to such
alterations or other work to require Tenant at the expiration of this Lease to
restore the Demised Premises to substantially the same condition as existed at
the Term Commencement Date.

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

     Whenever Tenant shall make any alterations, decoration, installations,
removals. Additions or improvements or do any other work in or to the Demised
Premises, Tenant will strictly observe the following covenants and agreements:

          (a)  In no event shall any material or equipment be incorporated in or
added to the Demised Premises in connection with any such alteration,
decoration, installation, addition or improvement which is subject to any lien,
charge, mortgage or other encumbrance of any kind whatsoever or is subject to
any security interest or any form of title retention agreement.  Any mechanic's
lien filed against the Demised Premises or the Building for work claimed to have
been done for, or materials claimed to have been furnished to Tenant shall be
discharged by Tenant within thirty, (30) days thereafter, at the expense of
Tenant, by filing the bond required by law or otherwise.  If Tenant fails so to
discharge any lien, Landlord may do so at Tenant's expense and Tenant shall
reimburse Landlord for any expense or cost incurred by Landlord in so doing
within fifteen (15) days after rendition of a bill therefor.

          (b)  All installations or work done by Tenant under this or any other
Article of this Lease shall be at its own expense (unless expressly otherwise
provided) and shall at all times comply with (i) laws, rules, orders and
regulations of governmental authorities having jurisdiction thereof: (ii)
orders, rules and regulations of any Board of Fire Underwriters, or any other
body hereafter constituted exercising similar functions, and governing insurance
rating bureaus: (iii) plans and specifications prepared by and at the expense of
Tenant theretofore submitted to Landlord for its prior written approval.
<PAGE>

          (c)  Tenant shall procure all necessary permits before undertaking any
work in the Demised Premises; do all such work in a good and workmanlike manner,
employing materials of good quality and complying with all governmental
requirements and defend, save harmless, exonerate and indemnify Landlord from
all injury, loss or damage to any person or property occasioned by or growing
out of such work.

12.  REPAIRS AND SECURITY BY TENANT

     Tenant shall keep or cause to be kept all and singular the Demised Premises
neat and clean and in such repair, order and condition as the same are in on the
Term Commencement Date or may be put in during the term hereof, reasonable use
and wear thereof. damage by fire or by other insured casualty and repairs
required to be made hereunder by Landlord excepted.  Without limiting, the
generality of the foregoing, Tenant shall keep all windows and other glass
whole, and shall replace the same whenever broken with glass of the same
quality.

     Tenant shall make, as and when needed as a result of misuse by, or neglect
or improper conduct (including without limitation the placement of any weight
exceeding the floor load) of Tenant or Tenant's servants, employees, agents,
invitees or licensees or otherwise, all repairs in and about the Demised
Premises necessary to preserve them in such repair, order and condition, which
repairs shall be in quality and class equal to the original work.  Landlord may
elect, at the expense of Tenant, either pursuant to Section 15.3 or otherwise,
to make any such repairs or to repair any damage or injury to the Building or
the Demised Premises caused by moving property of Tenant in or out of the
Building, or by installation or removal of furniture or other property, or by
misuse by, or neglect or improper conduct of, Tenant or Tenant's servants,
employees, agents or licensees.

13.  INSURANCE.  INDEMNIFICATION, EXONERATION AND EXCULPATION

     13.1 Insurance.  Tenant shall procure, keep in force and pay for (a)
          ---------
Comprehensive Public Liability Insurance indemnifying Landlord, any managing
agent designated by Landlord, Tenant and (whenever Landlord shall so request)
any Mortgagee against all claims and demands for injury to or death of persons
or damage to property which may be claimed to have occurred upon the Demised
Premises in the amounts which shall at the time Tenant and/or contractors enter
the Premises in accordance with Article 4 of this Lease be not less than Two
Hundred Thousand Dollars ($200,000) for property damage, One Million Dollars
($1,000,000) for injury or death of one person. and Two Million Dollars
($2,000,000) for injury or death of more than one person in a single incident,
and from time to time thereafter shall be not less than such higher amounts, if
procurable. as may be reasonably required by Landlord and are customarily
carried by responsible office tenants in the Greater Boston area, (b) insurance
covering any damage to the plate class windows in or immediately about the
Demised Premises, in reasonable amounts to be established from time to time by
Landlord, and (c) so-called contents and improvements insurance adequately
insuring all property belonging to or removable by Tenant and situated in the
Demised Premises.
<PAGE>

     13.2 Certificates of Insurance.  Such insurance shall be effected with
          -------------------------
insurers authorized to do business in Massachusetts under valid and enforceable
policies. and such policies shall name Landlord, each Mortgagee, Tenant and any
additional parties designated by Landlord pursuant to Section 13. 1 as the
insureds, as their respective interests appear.  Such insurance shall provide
that it shall not be cancelled without at least ten (10) days' prior written
notice to each insured named therein.  On or before the Term Commencement Date
and thereafter not less than fifteen (15) days prior to the expiration date of
each expiring policy, certificates of the policies provided for in Section 13.1
issued by the respective insurers, setting forth in full the provisions thereof
and issued by such insurers together with evidence satisfactory to Landlord of
the payment of all premiums for such policies, shall be delivered by Tenant to
Landlord and certificates as aforesaid of such policies shall, upon request of
Landlord, be delivered by Tenant to the holder of any mortgage affecting the
Demised Premises.

     13.3 General.  Tenant will save Landlord harmless, and will exonerate
          -------
and indemnify Landlord. from and against any and all claims, liabilities or
penalties asserted by or on behalf of any person. firm, corporation or public
authority:

          (a)  On account of or based upon any injury to person, or loss of or
damage to property sustained or occurring on the Demised Premises on account of
or based upon the act, emission. fault. negligence or misconduct of any person
whomsoever (other than Landlord or its agents, contractors or employees);

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

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

          (d)  On account of or resulting from the failure of Tenant to perform
and discharge any of its covenants and obligations under this Lease;

and, in respect of any of the foregoing items (a) - (d), from and against all
costs, expenses (including reasonable attorneys' fees), and liabilities incurred
in or in connection with any such claim, or any action or proceeding brought
thereon; and in case any action or proceeding be brought against Landlord by
reason of any such claim.  Tenant upon notice from Landlord shall fit Tenant's
expense resist or defend such action or proceeding and employ counsel therefor
<PAGE>

reasonably satisfactory to Landlord, it being agreed that such counsel may act
for insurance underwriters of Tenant engaged in such defense shall be deemed
satisfactory.

     13.4 Property of Tenant.  In addition to and not in limitation of the
          ------------------
foregoing, Tenant covenants and agrees that all merchandise, furniture, fixtures
and property of every kind, nature and description which may be in or upon the
Demised Premises or Building, in the public corridors, or on the sidewalks,
areaways and approaches adjacent thereto, during the term hereof, shall be it
the sole risk and hazard of Tenant, and that if the whole or any part thereof
shall be damaged, destroyed, stolen or removed from any cause or reason
whatsoever no part of said damage or loss shall be charged to, or borne by
Landlord.

     13.5 Bursting of Pipes, etc.  Landlord shall not be liable for any
          ----------------------
injury or damage to persons or property resulting from fire, explosion, falling
plaster, steam, gas, electricity, electrical disturbance, water, rain or snow or
leaks from any part of the Building or from the pipes, appliances or plumbing
works or from the roof, street or sub-surface or from any other place or caused
by dampness or by any other cause of whatever nature, unless caused by or due to
the negligence of Landlord, its agents, servants or employees, and then only
after (i) notice to Landlord of the condition claimed to constitute negligence
an (ii) the expiration of a reasonable time after such notice has been received
by Landlord without such condition having been cured or corrected: and in no
event shall Landlord be liable for any loss, the risk of which is compensated by
Tenant's insurance; nor shall Landlord or its agents be liable for any such
damages caused by other tenants or persons in the Building or caused by
operations in construction of any private, public or quasi-public work.

     13.6 Repairs and Alterations - No Diminution of Rental Value.  Except as
          -------------------------------------------------------
otherwise provided in Articles 16 or 18, there shall be no allowance to Tenant
for diminution of rental value and no liability on the part of Landlord by
reason of inconvenience, annoyance or injury to Tenant, resulting from any
repairs, alterations, additions, replacements or improvements made by Landlord,
Tenant or others in or to any portion of the Building or Demised Premises, or in
or to fixtures, appurtenances, or equipment thereof, or for failure of Landlord
or others to make any repairs, alterations, additions or improvements in or to
any portion of the Building or of the Demised Premises, or in or to the
fixtures, appurtenances or equipment thereof provided, however. that any such
work performed by or on behalf of Landlord shall be subject to the provisions of
Section 15.2.

14.  ASSIGNMENT, MORTGAGING, SUBLETTING, ETC.

     14.1 Restrictions.  Tenant covenants and agrees that neither this Lease
          ------------
nor the term and estate hereby granted nor any interest herein or therein, will
be assigned, sublet, mortgaged, pledged, encumbered or otherwise transferred
(whether voluntarily or by operation of law) and that neither the Demised
Premises, nor any part thereof, will be encumbered in any manner by reason of
an), act or omission on the part of Tenant, or used or occupied, or permitted to
be used or occupied, or utilized for any reason whatsoever, by anyone other than
Tenant, or for any use or purpose other than a stated in Article I without the
prior written consent of Landlord in every case.
<PAGE>

     14.2 Requests to Assign or Sublet.  In connection with any request by
          ----------------------------
Tenant for such consent to assign or sublet, Tenant shall submit to Landlord, in
writing, a statement containing the name of the proposed assignee or subtenant,
such information as to its financial responsibility and  standing as Landlord
may reasonably require, and all of the terms and provisions upon which the
proposed assignment or subletting is to be made, and, unless the proposed area
to be assigned or sublet shall constitute an entire floor or floors, such
statement shall be accompanied by a floor plan delineating the proposed area to
be assigned or sublet.  As long as Tenant is not in default under any of the
terms, covenants and conditions of this Lease on Tenant's part to be observed
and performed, Landlord shall not unreasonably withhold or delay Landlord's
prior consent to the assignment or subletting(s) by Tenant of all or parts of
the Demised Premises.  Each such subletting be for undivided occupancy by the
subtenant of that part of the Demised Premises affected thereby for the use
permitted under this Lease and at no time shall there be more than three (3)
occupants, including Tenant, within the Demised Premises.  Landlord may.
however. withhold such consent if, in Landlord's reasonable judgment, the
proposed assignee or subtenant is not engaged in a business consistent with the
character and dignity of the Building, or will impose any additional material
burden upon Landlord in the operation of the Building (to an extent greater than
the burden to which Landlord would be been put if Tenant continued to use, or
used. such part of the Demised Premises for its own purposes), or if  Landlord
has any other reasonable objections to the proposed assignment or subletting.

     14.3 Exceptions.  Notwithstanding the foregoing, Tenant may, without the
          ----------
requirements of obtaining Landlord's consent, assign this Lease or sublease any
portion of the Demised Premises to any entity which is the parent, a majority-
owned subsidiary of Tenant, an entity under common control with Tenant or to any
entity with which Tenant may sell all or substantially all of its assets as a
going concern (such entity with which Tenant may merge, consolidate or to which
Tenant may sell all or substantially all of its assets as aforesaid being
hereinafter referred to as a "Successor"), provided that simultaneously with any
such assignment, Tenant may sell all or substantially all of its assets as
aforesaid being hereinafter referred to as a "Successor"), provided that,
simultaneously with any such assignment.  Tenant shall deliver to Landlord an
agreement in form and substance reasonably satisfactory to Landlord which
contains an appropriate covenant of assumption by such assignee: provided
further that in the case of any such assignment or sublease to a Successor,
Tenant shall have submitted to Landlord prior thereto financial statements or
other materials reasonably satisfactory to Landlord evidencing that such
Successor has financial resources comparable to that of Tenant as of the time of
such assignment or sublease.

     14.4 Excess Rent.  If the rent received by Tenant on account of a
          -----------
sublease of all or any portion of the Demised Premises exceeds the Yearly Fixed
Rent and Additional Rent, allocated to the space subject to the sublease in the
proportion of the area of such space to the area of the entire Demised Premises,
Tenant shall pay to Landlord sixty percent (60%) of such excess. monthly as
received by Tenant.

     14.5 Recapture.  Notwithstanding the foregoing provisions of this
          ---------
Article: (1) in the event Tenant proposes to assign or sublet all of the Demised
Premises, Landlord, at Landlord's
<PAGE>

option, may give to Tenant, within ten (10) business days after the submission
by Tenant to Landlord of the statement required to be submitted in connection
with such assignment or subletting, or, if Tenant so requests, within ten (10)
business days after Tenant notifies Landlord that Tenant wishes to undertake
such assignment or subletting, but has not yet procured a proposed assignee or
subtenant, a notice terminating this Lease on the date (referred to as the
"Earlier Termination Date") immediately prior to the proposed commencement date
of the term of the proposed assignment or subletting, a set forth in such
statement, and, in the event such notice is given, this Lease and the Term shall
come to an end and expire on the Earlier Termination Date with the same effect
as if it were the date originally fixed in this Lease for the end of the Term of
this Lease, and the Rent shall be apportioned as of said Earlier Termination
Date and any prepaid portion of Rent for any period after such date shall be
refunded by Landlord to Tenant, provided, however that in the event Landlord
shall so elect to terminate this Lease, Tenant, upon written notice to Landlord
given within ten (10) days of receipt by Tenant of Landlord's notice of
termination, may elect to negate such termination by declaring its intent not to
proceed with such assignment or subletting; or (2) in the event Tenant proposes
to assign or sublet in the aggregate in excess of fifty percent (50%) of the
original square footage of the Demised Premises, Landlord at Landlord's option,
may give to Tenant fifty percent (50%) of the original square footage of the
Demised Premises. Landlord at Landlord's option, may give to Tenant, within
thirty (30) days after the submission by Tenant to Landlord of the statement
required to be submitted in connection with such proposed assignment of
subletting, a notice electing to eliminate such portion of the Demised Premises
(said portion is referred to as the "Eliminated Space") from the Demised
Premises during the period (referred to as the "Elimination Period") commencing
on the date (referred to as the "Elimination Date") immediately prior to the
proposed commencement date of the term of the proposed assignment or subletting,
as set forth in such statement, and ending on the proposed expiration date of
the term of the proposed assignment or subletting, as set forth in such
statement, and in the event such notice is given (i) the Eliminated Space shall
be eliminated from the Demised Premises during the Elimination Period; (ii)
Tenant shall surrender the Eliminated Space to Landlord on or prior to the
Elimination Date in the same manner as if said Date were the date originally
fixed in this Lease for the end of the Term of this Lease; (iii) if the
Eliminated Space shall constitute less than an entire floor, Landlord, at
Landlord's expense, shall have the right to make any alterations and
installations in the Demised Premises required, in Landlord's judgment,
reasonably exercised, to make the Eliminated Space a self-contained rental unit
with access through corridors to the elevators and core toilets serving the
Eliminated Space, and if the Demised Premises shall contain any core toilets or
any corridors (including any corridors proposed to be constructed by Landlord
pursuant to this subdivision (iii) providing access from the Eliminated Space to
the core area), Landlord and tenant or other occupant of the Eliminated Space
shall have the right to use such toilets and corridors in common with Tenant and
any other permitted occupants of the Demised Premises, and the right to install
signs and directional indicators in or about such corridors indicating the name
and location of such tenant or other occupant; (iv) during the Elimination
Period, the Yearly Fixed Rent shall be reduced in the proportion which the are
of the Eliminated Space bears to the total area of the Demised Premises
immediately prior to the Eliminate Date (including an equitable portion of the
area of any corridors referred to in subdivision (iii) of this sentence as part
of the area of the Eliminated Space for the purpose of computing such reduction,
and any prepaid Rent for any period after the Elimination Date
<PAGE>

allocable to the Eliminated Space shall be refunded by Landlord to Tenant; (v)
there shall be an equitable apportionment of any Additional Rent Payable
pursuant to Article 6 for the relevant fiscal and calendar years in which said
Elimination Date shall occur; and (vi) if the Elimination Period shall end prior
to the date originally fixed in this Lease for the end of the Term of this
Lease, the Eliminated Space, in its then existing condition, shall be deemed
restored to an once again a part of the Demised Premises subject to the
provisions of this Lease as if said elimination had not occurred during the
period (referred to as the "Restoration Period") commencing on the date next
following the expiration of the Elimination Period and ending on the date
originally fixed in this Lease for the end of the Term of this Lease, except in
the event that Landlord is unable to give Tenant possession of the Eliminated
Space at the expiration of the Elimination Period by reason of the holding over
or retention of possession of any tenant or other occupant, in which event (x)
the Restoration Period shall not commence, and the Eliminated Space shall not be
deemed restored to or a part of the Demised Premises, until the date upon which
Landlord shall give Tenant possession of such Space free of occupancies,
provided Landlord shall use reasonable efforts to return the Eliminated Space to
Tenant at the expiration of the Elimination Period, (y) neither the date fixed
in this Lease for the end of the Term of the Lease, not the validity of this
Lease shall be affected and (z) Tenant waives any right to recover any donates
which may result from the failure of Landlord to deliver possession of the
Eliminated Space at the end of the Elimination Period excepting only those
resulting from Landlord's gross negligence or willful misconduct.

     14.6 Further Documentation.  At the request of Landlord, Tenant shall
          ---------------------
execute and deliver an instrument or instruments, in form satisfactory to
Landlord, setting forth any modifications to this Lease contemplated in or
resulting from the operation of the foregoing provisions of this paragraph
however, neither Landlord's failure to request any such instrument nor Tenant's
failure to execute or deliver any such instrument shall vitiate the effect of
the foregoing provisions of this Article.

     14.7 General.
          -------

          (a)  The failure by Landlord to exercise its option under this
paragraph with respect to any subletting shall not be deemed a waiver of such
option with respect to any extension or any subsequent subletting of the
premises affected thereby.  Tenant shall reimburse Landlord promptly, as
Additional Rent, for reasonable legal and other and other expense incurred by
Landlord in connection with any request by Tenant for any consent required under
the provisions of areas Article.

          (b)  It is specifically understood and agreed that neither Tenant nor
any other person having an interest in the possession, use, occupancy or
utilization of the Demised Premises shall enter into any sublease, license,
concession or other agreement (or renewals of any of the foregoing) for use,
occupancy or utilization of space in the Demised Premises which provides for
rental or other payment for such use, occupancy or utilization based, in whole
or in part. on the net income or profits derived by any person or entity from
the space leased, used, occupied or utilized (other than an amount based on a
fixed percentage or percentages of receipts or sales).  Any such purported
sublease or other agreement shall be absolutely void and
<PAGE>

ineffective as a conveyance of any right or interest in the possession, use,
occupancy, or utilization of any part of the Demised Premises.

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

          (d)  If this Lease be assigned, or if the Demised Premises or any part
thereof shall be sublet or occupied by anybody other than Tenant, Landlord may
at any time and from time to time, collect rent and other charges from the
assignee, subtenant or occupant and apply the aggregate amount collected to the
Rent and other charges herein reserved, but no such assignment or collection
shall be deemed a waiver of this covenant, or the acceptance of the assignee.
subtenant or occupant as a tenant, or a release of Tenant from the further
performance by tenant of covenants on the part of Tenant herein contained.
Landlord shall notify Tenant of any amounts so collected by Landlord directly
from such subtenant or assignee.  The consent by Landlord to an assignment or
subletting or occupancy shall not in any way be construed to relieve Tenant from
obtaining the express consent in writing of Landlord to any further assignment
or subletting or occupancy.

15.  MISCELLANEOUS COVENANTS

     15.1 Rules and Regulations.  Tenant and Tenant's servants, employees,
          ---------------------
and agents will faithfully observe such Rules and Regulations as are attached
hereto as Exhibit E and made a part hereof or as Landlord hereafter at any time
          ---------
or from time to time may make and may communicate in writing to Tenant and which
in the reasonable judgment of Landlord shall be necessary for the reputation,
safety, care or appearance of the Property, or the preservation of good order
therein, or the operation or maintenance of the Property, or the equipment
thereof, or the comfort of tenants or others in the Building, provided, however,
that in the case of any conflict between the provisions of this Lease and any
such Rules and Regulations, the provisions of this Lease shall control, and
provided further that nothing contained in this Lease shall be construed to
impose upon Landlord any duty or obligation to enforce such Rules and
Regulations or the terms, covenants or conditions in any other lease as against
any other tenant and Landlord shall not be liable to Tenant for violation of the
same by any other tenant, its servants, employees, agents, visitors, invitees or
licensees.

     15.2 Access to Premises - Shoring.  Tenant shall: (i) permit Landlord to
          ----------------------------
erect, use and maintain pipes, ducts and conduits in and through the Demised
Premises, provided the same do not materially reduce the floor area or
materially adversely affect the appearance thereof; (ii) permit the Landlord and
any Mortgagee of the Building or the Building and Land or of the interest of
Landlord therein, and any lessor under any ground or underlying lease, and their
representatives, to have free and unrestricted access to and to enter upon the
Demised Premises at all reasonable hours for the purposes of inspection or of
making repairs, replacements or improvements in or to the Demised Premises or
the Building or equipment (including, without
<PAGE>

limitation, sanitary, electrical, heating, air conditioning or other systems) or
of complying with all laws, orders and requirements of governmental or other
authority or of exercising any right reserved to Landlord by this Lease
(including the right during the progress of any such repairs, replacements or
improvements or while performing work and furnishing materials in connection
with compliance with any such laws, orders or requirements to take upon or
through or to keep and store within, the Demised Premises all necessary
materials, tools and equipment); and (iii) permit Landlord, at reasonable times,
to show Demised Premises during ordinary business hours to any Mortgagee, ground
lessor, prospective purchaser, or prospective assignee of any mortgage, of the
Building, or of the Building, and the Land or of the interest of Landlord
therein, and during the period of twelve months next preceding the Termination
Date to any person contemplating the leasing of the Demised Premises or any part
thereof. If during the last month of the Term, Tenant shall have removed all of
Tenant's property therefrom. Landlord may immediately enter and alter, renovate
and redecorate the Demised Premises without elimination or abatement of rent, or
incurring liability to Tenant for any compensation and such acts shall have no
effect upon this Lease. If Tenant shall not be personally present to open and
permit any entry into the Demised Premises at any time when for any reason an
entry therein shall be necessary or permissible, Landlord or Landlord's agents
must nevertheless be able to gain such entry by contacting a responsible
representative of Tenant, whose name, address and telephone number shall be
furnished by Tenant. Provided that Landlord shall incur no additional expense
thereby, Landlord shall exercise its rights of access to the Demised Premises
permitted under any of the terms and provisions of this Lease in such manner as
to minimize to the extent practicable interference with Tenant's use and
occupation of the Demised Premises, and upon reasonable prior notice, except in
the case of an emergency or where such notice is not reasonably practical. If an
excavation shall be made upon land adjacent to the Demised Premises or shall be
authorized to be made, Tenant shall afford, to the causing or authorized to
cause such excavation, license to enter upon the Demised Premises for the
purpose of doing such work as said person shall deem necessary to preserve the
Building from injury or damage and to support the same by proper foundations
without any claim for damage or indemnity against Landlord, or diminution or
abatement of Rent.

     15.3 Accidents to Sanitary and Other Systems.  Tenant shall give to
          ---------------------------------------
Landlord prompt notice of any fire or accident in the Demised Premises or in the
Building and of any damage to, or defective condition in, any part or
appurtenance of the Building's sanitary, electrical, heating and air
conditioning or other systems located in, or passing through, the Demised
Premises, and the damage of defective condition shall be remedied by Landlord
with reasonable diligence, but if such damage or defective condition was caused
by Tenant or by the employees, licensees, or invitees of Tenant, the cost to
remedy the same shall be paid by Tenant.  Tenant shall not be entitled to claim
any eviction from the Demised Premises or any damages arising from all such
damage or defect unless the same (i) shall have been occasioned by the
negligence of Landlord, its agents, servants or employees and (ii) shall not,
after notice to Landlord of the condition claimed to constitute negligence, have
been cured or corrected within a reasonable time after such notice his been
received by Landlord; and in case of a claim of eviction unless such damage or
defective condition shall have rendered the Demised Premises untenantable and
they shall not have been made tenantable by Landlord within a reasonable time.
Landlord agrees to diligently work to correct such damage or defect, except as
otherwise provided herein.
<PAGE>

     15.4 Signs, Blinds and Drapes.  Tenant shall not place any signs on the
          ------------------------
exterior of the Building or on or in any window, public corridor or door visible
from the exterior of the Demised Premises.  No blinds may be put on or in any
window nor may any Building drapes or blinds be removed by Tenant.  Tenant may
hang its own drapes, provided that they shall not, without the prior written
approval of Landlord, in any way interfere with any Building drapery or blinds
or he visible from the exterior of the Building.

     15.5 Estoppel Certificate.  Either party shall at any time and from time
          --------------------
to time upon not less than twenty (20) days' prior notice by Landlord to Tenant
or by a Mortgagee to Tenant, or by Tenant to Landlord, as the case may be,
execute, acknowledge and deliver to the party making such request a statement in
writing certifying that this Lease is unmodified and in full force and effect
(or if there have been modifications, that the same is in full force and effect
as modified and stating! the modifications) and the dates to which Rent has been
paid in advance, if any, and stating whether or not to the best knowledge of the
signer of such certificate Landlord is in default in performance of any
covenant, agreement, term, provisions or condition contained in this Lease and,
if so, specifying each such default of which the signer may have knowledge, it
being intended that any such statement delivered pursuant hereto may be relied
upon by any prospective purchaser of the Building or of the Building and the
Land or of the interest of Landlord therein, any Mortgagee or prospective
Mortgagee thereof, any lessor or prospective lessor thereof, any lessee or
prospective lessee thereof, or any prospective assignee of any Mortgage.  The
form of ;any such estoppel certificate requested by a Mortgagee shall be
satisfactory to such Mortgagee.  Notwithstanding anything contained in this
Lease to the contrary, the provisions of this Section 15.5 shall be inapplicable
to Teachers Insurance and Annuity Association in the event said entity shall
succeed to the rights of Landlord hereunder.

     15.6 Prohibited Items.  Tenant shall not bring or permit to be brought
          ----------------
or kept in or on the Demised Premises or elsewhere in the Building any
hazardous, inflammable, combustible or explosive fluid, material, chemical or
substance (except such as are related to Tenant's use of the Demised Premises,
provided that the same are stored and handled in a proper fashion consistent
with all applicable legal standards).

     15.7 Requirements of Law; Fines and Penalties.  Tenant at its sole
          ----------------------------------------
expense shall comply with all laws, rules, orders and regulations of Federal,
State, County and Municipal Authorities and with any direction of any public
officer or officers, pursuant to law, which shall impose any duty upon Landlord
or Tenant with respect to and arising out of Tenant's use or occupancy of the
Demised Premises.  Tenant shall reimburse and compensate Landlord for all
expenditures made by, or damages or fines sustained or incurred by, Landlord due
to nonperformance or noncompliance with or breach or failure to observe any
term, covenant or condition of this Lease upon Tenant's part to be kept,
observed, performed or complied with.  If Tenant receives notice of any
violation of law, ordinance, order or regulation applicable to the Demised
Premises, it shall give prompt notice thereof to Landlord.

     15.8 Tenant's Acts - Effect on Insurance.  Except for permitted uses,
          -----------------------------------
Tenant shall not do or permit to be done any act or thing upon the Demised
Premises or elsewhere in the Building
<PAGE>

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

     15.9  Hazardous Materials.  Tenant shall not (either with or without
           -------------------
negligence) cause or permit the escape, disposal or release of any biologically
or chemically active or other hazardous substances or materials.  Tenant shall
not allow the storage or use of such substances or materials in any manner not
sanctioned by law or by the highest standards prevailing in the industry for the
storage and use of such substances or materials, nor allow to be brought onto
the Property any such materials or substances except to use in the ordinary
course of Tenant's business, and then only after written notice is given to
Landlord of the identity of such substances or materials.  Without limitations
hazardous substances and materials shall include those described in the
Comprehensive Environmental Response, Compensation and Liability Act of 1980, as
amended, 42 U.S.C. Section 9601 et seq., any applicable state or local laws and
the regulations adopted under these acts.  If any lender or Governmental agency
shall ever require testing to ascertain whether or not there has been any
release of hazardous materials, then the reasonable costs thereof shall be
reimbursed by Tenant to Landlord upon demand as additional charges if such
requirement applies to the Demised Premises.  In addition, Tenant shall execute
affidavits, representations and the like from time to time at Landlord's request
concerning Tenant's best knowledge and belief regarding the presence of
hazardous substances or materials on the Demised Premises.  In all events,
Tenant shall indemnify Landlord in the manner elsewhere provided in this Lease
from any release of hazardous materials on the Demised Premises occurring while
Tenant is in possession, or elsewhere if caused by Tenant or persons acting
under Tenant.  The within covenants shall survive the expiration or earlier
termination of the Term of this Lease.

     15.10 Miscellaneous.  Tenant shall not suffer or permit the Demised
           -------------
Premises or any fixtures, equipment or utilities therein or serving the same, to
be overloaded, damages or defaced, nor permit any hole to be drilled or made in
any part thereof.

<PAGE>

16.  DAMAGE BY FIRE, ETC.

     In the event of loss of, or damage to, the Demised Premises or the Building
by fire or other casualty, the rights and obligations of the parties hereto
shall be as follows:

          (a) If the Demised Premises, or any part thereof, shall be damaged by
fire or other casualty.  Tenant shall give prompt notice thereof to Landlord,
and Landlord, upon receiving such notice, shall proceed promptly and with due
diligence, subject to unavoidable delays, to repair, or cause to be repaired,
such damage.  If the Demised Premises or any part thereof shall be rendered
untenantable by reason of such damage, whether to the Demised Premises or to the
Building, the Yearly Fixed Rent and Additional Rent shall proportionately abate
for the period from the date of such damage to the date when such damage shall
have been repaired.

          (b) If, as a result of fire or other casualty, the whole or a
substantial portion of the Building is rendered untenantable, Landlord, within
ninety (90) days from the date of such fire or other casualty, may terminate
this Lease by notice to Tenant, specifying a date not less than twenty (20) nor
more than forty (40) days after the giving of such notice on which the Term of
this Lease shall terminate.  If Landlord does not so elect to terminate this
Lease, then Landlord shall proceed with diligence to repair the damage to the
Demised Premises and all facilities serving the same, if any, which shall have
occurred, and the Yearly Fixed Rent and Additional Rent shall meanwhile
proportionately abate, all as provided in Paragraph (a) of this Section.
However, if, in the event of any damage by fire or other casualty, such damage
is not repaired and the Demised Premises and all facilities serving the same
restored to substantially the same condition as they were prior to such damage
within six (6) months from the date of such damage, Tenant within thirty (30.)
days from the expiration of such six (6) month period, may terminate its Lease
by notice to Landlord, specifying a date not more than sixty (60) days after the
giving of such notice on which the term of this Lease shall terminate.

          (c) If the Demised Premises shall be rendered untenantable by fire or
other casualty during the last two (2) years of the Term of this Lease, Landlord
may terminate this Lease effective as of the date of such fire or other casualty
upon notice to Tenant given within thirty (30) days after such fire or other
casualty.

          (d) Landlord shall not be required to repair or replace any of
 Tenant's business machinery, equipment, cabinet work, furniture, personal
 property or other installations (which shall, however, be substantially
 restored by Tenant within ninety (90) days after Landlord shall have completed
 any repair or restoration required under the terms of this Article), and no
 damages compensation or claim shall be payable by Landlord for inconvenience,
 loss of business or annoyance arising from any repair or restoration of any
 portion of the Demised Premises or of the Building.

          (e) The provisions of this Article shall be considered an express
agreement governing any instance of damage or destruction of the Building or the
Demised Premises by fire or other casualty, and any law now or hereafter in
force providing for such a contingency in the absence of express agreement shall
have no application.
<PAGE>

          (f) In the event of any termination of this Lease pursuant to this
Article, the Term of this Lease shall expire as of the effective termination
date as fully and completely as if such date were the date herein originally
scheduled as the Termination Date.  Tenant shall have access to the Demised
Premises for a period of thirty (30) days after the date of termination in order
to remove Tenant's personal property.

          (g) Landlord's Architect's certificate, given in good faith, shall be
deemed conclusive of the statements therein contained and binding upon Tenant
with respect to the performance and completion of any repair or restoration work
undertaken by Landlord pursuant to this Article or Article 18.  Any minor or
insubstantial details of construction or mechanical adjustments which remain to
be done after the delivery of said certificate shall be handled on a punch list
basis and thereafter promptly completed by Landlord.

17.  WAIVER OF SUBROGATION

     In any case in which Tenant shall be obligated under any provision of this
Lease to pay to Landlord any loss, cost, damage, liability, or expense suffered
or incurred by Landlord, Landlord shall allow to Tenant as an offset against the
amount thereof the net proceeds of any insurance collected by Landlord for or on
account of such loss, cost, damage, liability or expense, provided that the
allowance of such offset does not invalidate or prejudice the policy or policies
under which such proceeds were payable.

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

     The parties hereto shall each endeavor to procure an appropriate clause in,
or endorsement on, any fire or extended coverage insurance policy covering the
Demised Premises and the Building and personal property, fixtures and equipment
located thereon or therein, pursuant to which the insurance companies waive
subrogation or consent to a waiver of right of recovery, and having obtained
such clauses and/or endorsements of waiver of subrogation or consent to a waiver
of right of recovery each party hereby agrees that it will not make any claim
against or seek to recover from the other for any loss or damage to its property
or the property of others resulting from fire or other perils covered by such
fire and extended coverage insurance; provided, however, that the release,
discharge, exoneration and covenant not to sue herein contained shall be limited
by the terms and provisions of the waiver of subrogation clauses and/or
endorsements or clauses and/or endorsements consenting to a waiver of right of
recovery and shall be coextensive therewith.  If either party may obtain such
clause or endorsement only
<PAGE>

upon payment of an additional premium, such party shall promptly so advise the
other party and shall be under no obligation to obtain such clause or
endorsement unless such other party pays the premium.

18.  CONDEMNATION - EMINENT DOMAIN

     In the event that the whole or any material part of the Building shall be
taken or appropriated by eminent domain or shall be condemned for any public or
quasi-public use, or (by virtue of any such taking, appropriation or
condemnation) shall suffer any damage (direct, indirect or consequential) for
which Landlord or Tenant shall be entitled to compensation then (and in any such
event) this Lease and the Term hereof may be terminated at the election of
Landlord by a notice in writing of its election so to terminate which shall be
given by the Landlord to Tenant within sixty (60) days following the date on
which Landlord shall have received notice of such taking, appropriation or
condemnation.  In the event that more than twenty-five percent (25%) of the
floor area of the Demised Premises shall be so taken, appropriated or condemned,
then (and in any such event) this Lease and the Term hereof may be terminated at
the election of Tenant by a notice in writing of its election so to terminate
which shall be given by Tenant to Landlord within sixty (60) days following the
date on which Tenant shall have received notice of such taking, appropriation or
condemnation.

          Upon the giving of any such notice of termination (either by Landlord
or Tenant) this Lease and the Term hereof shall terminate on or retroactively as
of the date on which Tenant shall be required to vacate any part of the Demised
Premises or shall be deprived of a substantial part of the means of access
thereto, provided, however, that Landlord may in Landlord's notice elect to
terminate this Lease and the Term hereof retroactively as of the date on which
such takings, appropriation or condemnation became legally effective.  In the
event of any such termination, this Lease and the Term hereof shall expire as of
the effective termination date as fully and completely as if such date were the
date herein originally scheduled as the Termination 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 Demised
Premises, or the remainder of the means of access, as nearly as practicably may
be to the same condition as obtained prior to such taking, appropriation or
condemnation in which event (i) a just proportion of the Yearly Fixed Rent and
Additional Rent, accordance to the nature and extent of the taking,
appropriation or condemnation and the resulting permanent injury to the Demised
Premises and the means of access thereto, shall be permanently abated, and (ii)
a just proportion of the remainder of the Yearly Fixed Rent and Additional Rent,
according to the nature and extent of the taking, appropriation or condemnation
and the resultant injury sustained by the Premises and the means of access
thereto, shall be abated until what remains of the Premises and the means of
access thereto shall have been restored as fully as may be for permanent use and
occupation by Tenant hereunder.  Except for any award specifically reimbursing
Tenant for moving or relocation expenses and Tenant's removable fixtures and
equipment, 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 and
retain all such compensation and damages, grants to Landlord all and whatever
rights (if any) Tenant may have
<PAGE>

to such compensation and damages, and agrees to execute and deliver all and
whatever further instruments of assignment as Landlord may from time to time
request. In the event of any taking of the Demised Premises or any part thereof
for temporary use, (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 of this
Lease, such award shall be apportioned between Landlord and Tenant as of the
Termination Date.

19.  DEFAULT

     19.1  Conditions of Limitation - Re-entry - Termination.    This Lease and
           -------------------------------------------------
the herein term and estate are upon the condition that if (a) Tenant shall
neglect or fail to perform or observe any of the Tenant's covenants herein,
including (without limitation) the covenants with regard to the payment of Rent
on or before ten (10) days of its due date; or (b) Tenant shall be involved in
financial difficulties as evidenced by an admission in writing by Tenant of
Tenant's inability to pay its debts generally as they become due, or by the
making or offering to make a composition of its debts with its creditors; or (c)
Tenant shall make an assignment or trust mortgage, or other conveyance or
transfer of like nature, of all or a substantial part of its property for the
benefit of its creditors, or (d) the leasehold hereby created shall be taken on
execution or by other process of law and shall not be revested in Tenant within
sixty (60) days thereafter; or (e) a receiver, sequester, trustee or similar
officer shall be appointed by a court of competent jurisdiction to take charge
of all or a substantial part of Tenant's property and such appointment shall not
be vacated within sixty (60) days or (f) any proceeding shall be instituted by
or against Tenant pursuant to any of the provisions of any Act of Congress or
State law relating to bankruptcy, reorganization, arrangements, compositions or
other relief from creditors, and, in the case of any such proceeding instituted
against it, if Tenant shall fail to have such proceeding dismissed within thirty
(30) days or if Tenant is adjudged bankrupt or insolvent as a result of any such
proceeding; or any event shall occur or any contingency shall arise whereby this
Lease, or the term and estate thereby created would (by operation of law or
otherwise) devolve upon or pass to any person, firm or corporation other than
Tenant, except as expressly permitted under Article 14 hereof; or (h) Tenant
shall vacate all or substantially all of the Demised Premises then, and in any
such event (except as hereinafter in Article 19.2 otherwise provided) Landlord
may, in a manner consistent with applicable law, immediately or at any time
thereafter declare this Lease terminated by notice to Tenant or, without further
demand or notice, enter into and upon the Demised Premises (or any part thereof
in the name of the whole), and in either such case (and without prejudice to any
remedies which might otherwise be available for arrears of rent or other charges
due hereunder or preceding breach of covenant and without prejudice to Tenant's
liability for damages as hereinafter stated), this Lease shall terminate.  The
words "re-entry" and "re-enter" as used in this Lease are not restricted to
their technical legal meaning.

     19.2  Damages - Assignment for Benefit of Creditors.   For the more
           ---------------------------------------------
effectual securing by Landlord of the rent and other charge and payments
reserved hereunder, it is agreed as a further condition of this Lease that if at
any time Tenant shall make an assignment of its property for the benefit of its
creditors under the terms of which the debts provable by its creditors shall be
debts provable against the estate of insolvent debtors either under the laws of
the Commonwealth of Massachusetts or under some law or laws other than the
Bankruptcy Code as now or hereafter
<PAGE>

enacted then and in any such case the same shall constitute a breach of this
Lease, and the term and estate hereby created shall terminate ipso facto,
without entry or other action by Landlord. and notwithstanding any other
provisions of this Lease Landlord shall forthwith upon such termination, without
prejudice to any remedies which might otherwise be available for arrears of rent
or other charges due hereunder or preceding breach of this Lease, be ipso facto
entitled to recover its liquidated damages the sum of (a) the amount by which,
at the time of such termination of this Lease, (i) the aggregate of the Rent
projected over the period commencing with such termination and ending with the
Termination Date stated in Article 1 exceeds (ii) the aggregate projected rental
value of the Demised Premises for such period and (b) (in view of the
uncertainty of prompt re-letting and the expense entailed in re-letting the
Demised Premises) an amount equal to the Rent payable for and in respect of the
calendar year next preceding the date of termination, as aforesaid. Upon such
termination, Landlord, may immediately, or at any time thereafter, without
demand or notice, enter into or upon the Demised Premises (or any part thereof
in the name of the whole), and (without being taken or deemed to be guilty of
any manner of trespass or conversion, and without being liable to indictment,
prosecution or damages thereof) may forcibly if necessary, expel Tenant and
those claiming under Tenant from the Demised Premises and remove therefrom the
effects of Tenant and those claiming under Tenant.

     19.3  Damages - Termination.    Upon the termination of this Lease under
           ---------------------
the provisions of this Article then except as hereinabove in Section 19.2
otherwise provided, Tenant shall pay to Landlord the Rent payable by Tenant to
Landlord up to the time of such termination, shall continue to he liable for any
preceding breach of covenant, and in addition, shall pay to Landlord as damages,
at the election of Landlord,

     either:

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

     or,

     (y)   amounts equal to the Rent which would have been payable by Tenant had
this Lease not been so terminated, payable upon the due dates therefor specified
herein following such termination and until the originally scheduled Termination
Date as specified in Article 1, provided, however, if landlord shall re-let the
Demised Premises during such period, that Landlord shall credit Tenant with the
net rents received by Landlord from such re-letting, such net rents to be
determined by first deducting from the gross rents as and when received by
Landlord from such re-letting, the expenses incurred or paid by Landlord
termination of this Lease, as well as the expenses of re-letting, including
altering and preparing the Demised Premises for new tenants, brokers'
commissions, and all other similar and dissimilar expenses properly chargeable
against the Demised Premises and the rental therefrom, it being understood that
any such re-letting may be for a period equal to or shorter or longer than the
remaining term
<PAGE>

of this Lease; and provided, further, that (i) in no event shall Tenant be
entitled to receive any excess of such net rents over the sums payable by Tenant
to Landlord hereunder and (ii) in no event shall Tenant be entitled in any suit
for the collection of damages pursuant to this Subparagraph (y) to a credit in
respect of any net rents from a re-letting except to the extent that such net
rents are actually received by Landlord prior to such determination. If the
Demised Premises or any part thereof should be relet in combination with other
space, then proper apportionment on a square foot area basis shall be made of
the rent received from such re-letting and of the expenses of re-letting.

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

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

     19.4  Fees and Expenses.    If Tenant shall default in the performance of
           -----------------
any covenant on Tenant's part to be performed as in this Lease contained,
Landlord may immediately, or at any time thereafter, without notice, perform the
same for the account of Tenant.  If Landlord at any time is compelled to pay or
elects to pay any sum of money, or do any act which will require the payment of
any sum of money, by reason of the failure of Tenant to comply with any
provision hereof, or if Landlord is compelled to or does incur any expense,
including reasonable attorneys' fees, in instituting, prosecuting and/or
defending any action or proceeding instituted by reason of any default of Tenant
hereunder, Tenant shall on demand pay to Landlord by way of reimbursement the
sum or sums so paid by Landlord with all interest, costs and damages.  Without
limiting the generality of the foregoing, in the event that any Rent is in
arrears by more than ten (10) days after written notice thereof by Landlord to
Tenant, Tenant shall pay, as Additional Rent, a delinquency charge equal to one
and one-half percent (1-1/2%) of the arrearage for each calendar month (or
fraction thereof) during which it remains unpaid.

     19.5  Landlord's Remedies Not Exclusive.   The specified remedies to
           ---------------------------------
which Landlord may resort hereunder are cumulative and are not intended to be
exclusive of any remedies or means of redress to which Landlord may at any time
be lawfully entitled, and Landlord may invoke any remedy, (including, the remedy
of specific performance) allowed at law or in equity as if specific remedies
were not herein provided for.

     19.6  Grace Period.    Notwithstanding anything, to the contrary in this
           ------------
Article contained, Landlord agrees not to take any action to terminate this
Lease (a) for default by Tenant in the payment when due of Rent, if Tenant shall
cure such default within ten (10) days after written notice thereof given by
Landlord to Tenant, or (b) for default by Tenant in the performance of any other
covenant, if Tenant shall cure such default within a period of thirty (30) days
after written notice thereof given by Landlord to Tenant (except where the
nature of the default is such
<PAGE>

that remedial action should appropriately take place sooner as indicated in such
written notice), or with respect to covenants other than to pay a sum of money
within such additional period as may reasonably be required to cure such default
if (because of governmental restrictions or any other cause beyond the
reasonable control of Tenant) the default is of such a nature that it cannot be
cured within such thirty (30)-day period, provided, however, (1) that there
shall be no extension of time beyond such thirty (30)-day period for curing of
any such default unless, not more than ten (10) days after the receipt of the
notice of default, Tenant in writing (i) shall specify the cause on account of
which the default cannot be cured during such period and shall advise Landlord
of its intention duly to institute all steps necessary to cure the default and
(ii) shall as soon as may be reasonable, duly institute and thereafter
diligently prosecute to completion all steps necessary to cure such default and,
(2) that no notice of the opportunity to cure default need be given, and no
grace period whatsoever shall be allowed to Tenant, if the default is incurable
or if the covenant or condition, the breach of which gave rise to the default,
had, by reason of a breach on a prior occasion-been the subject of a notice
hereunder to cure such default.

20.  END OF TERM - ABANDONED PROPERTY

     Upon the expiration or other termination of the Term of this Lease, Tenant
shall peaceably quit and surrender to Landlord the Demised Premises and all
alterations and additions thereto which Tenant is not entitled or required to
remove under the provisions of this Lease, broom clean in good order, repair and
condition excepting only reasonable use and wear and damage by fire or other
casualty for which, under other provisions of this Lease, Tenant has no
responsibility of repair or restoration.  Tenant's obligation to observe or
perform this covenant shall survive the expiration or other termination of the
term of this Lease.

     Any personal property in which Tenant has an interest which shall remain in
the Building or on the Demised Premises after the expiration or termination of
the Term of this Lease shall be conclusively deemed to have been abandoned, and
may be disposed of in such manner as Landlord may see fit:  provided, however,
notwithstanding the foregoing, that Tenant will, upon request of Landlord made
not later than thirty (30) days after the expiration or termination of the term
hereof, promptly remove from the Building any such personal property or, if any
part thereof shall be sold, that Landlord may receive and retain the proceeds of
such sale and apply the same, at its option, against the expenses of the sale,
the cost of moving and storage, any arrears of Rent payable hereunder by Tenant
to Landlord and any damages to which Landlord may be entitled under Article 19
hereof or pursuant to law, with the balance if any, to be paid to Tenant.

21.  RIGHTS OF MORTGAGEES

     21.1  Superiority of Lease.    Except as provided in Section 21.7 hereof
           --------------------
and to the extent that it may be provided otherwise by written agreement between
Tenant and a Mortgagee, this Lease shall be superior, and shall not be
subordinated, to a Mortgage or to any other voluntary lien or encumbrance
affecting the Land or Building or any part thereof, provided, however, that
<PAGE>

such Mortgage shall be superior, and shall not be subordinated, to this Lease
with respect to the following:

     (a)   the prior right and claim under and the prior lien of said Mortgage
in, to and upon any award or other compensation heretofore or hereafter to be
made for any taking, by eminent domain of any part of the Demised Premises, and
as to the right of disposition thereof in accordance with the provisions of the
said Mortgage; or

     (b)   the prior right and claim under the prior lien of the said Mortgage,
in, to and upon any proceeds payable under all policies of fire and rent
insurance upon the Demised Premises, and as to the right of disposition thereof
in accordance with the terms of said Mortgage; or

     (c)   any lien, right, power or interest, if any, which may have arisen or
intervened in the period between the recording of the said Mortgage and the
execution of this Lease.

     21.2  Entry and Possession.    Upon entry and taking possession of the
           --------------------
Property by a Mortgagee, for the purpose of foreclosure or otherwise, such
Mortgagee shall have all the rights of landlord and shall be liable to perform
all the obligations of Landlord arising and accruing during the period of such
possession by such Mortgagee.

     21.3  Right to Cure.    No act or failure to act on the part of Landlord
           -------------
which would entitle Tenant under the terms of this Lease, or by law, to be
relieved of Tenant's obligations hereunder or to terminate this Lease, shall
result in a release or termination of such obligations or a termination of this
Lease unless (i) Tenant shall have first given written notice of Landlord's act
or failure to act to first Mortgagees of record, if any, and to any other
Mortgagees of record on the Term Commencement Date of the Lease or whom Tenant
has been given written notice, specifying the act or failure to act on the part
of Landlord which could or would give basis to Tenant's rights: and (ii) such
Mortgagees, after receipt of such notice, have failed or refused to correct or
cure the condition complained of within a reasonable time thereafter, but
nothing contained in this paragraph shall be deemed to impose any obligation on
any such Mortgagees to correct or cure any such condition.  "Reasonable time" as
used above means and includes a reasonable time to obtain possession of the Land
and Building if any such Mortgagee elects to do so and a reasonable time to
correct or cure the condition if such condition is determined to exist.

     21.4  Duty to Construct.    Notwithstanding any other provision to the
           -----------------
contrary contained in this Lease, if prior to substantial completion of
Landlord's obligations under Article 4 any holder of a Mortgage enters and takes
possession of the Property for the purpose of foreclosing such Mortgage, such
holder may elect, by written notice given to Tenant and Landlord at any time
within 90 days after such entry and taking possession, not to perform Landlord's
obligations under Article 4, and in such event such holder and all persons
claiming under it shall be relieved of all obligations to perform, and all
liability for failure to perform said Landlord's obligations under Article 4 and
Tenant may, without waiver of any rights which Tenant may have against Landlord,
terminate this Lease and all its obligations hereunder by written notice to
Landlord and such holder given within 30 days after the day on which such holder
shall have given its notice as aforesaid.
<PAGE>

     21.5  Prepaid Rent.    No Rent shall be paid more than thirty (30) days
           ------------
prior to the due dates thereof and, as to a first Mortgagee of record and any
other Mortgagees of whom Tenant has been given written notice, payments made in
violation of this provision shall (except to the extent that such rents are
actually received by such Mortgagee) be a nullity as against such Mortgagee and
Tenant shall be liable for the amount of such payments to such Mortgagee.

     21.6  Continuing Offer.    The covenants and agreements contained in this
           ----------------
Lease with respect to the rights, powers and benefits of a Mortgagee
(particularly, without limitation thereby, the covenants and agreements
contained in this Article) constitute a continuing offer to any person,
corporation or other entity, which by accepting or requiring an assignment of
this Lease or by entity or foreclosure assumes the obligations herein set forth
with respect to such Mortgagee; every such Mortgagee is hereby constituted a
party to this Lease as an obligee hereunder to the same extent is though its
name was written hereon as such and such Mortgagee shall be entitled to enforce
such provisions in its own name.

     21.7  Subordination.  Notwithstanding the foregoing provisions of this
           -------------
Article, Tenant agrees at the request of Landlord or any Mortgagee, to execute
and deliver promptly any certificate or other instrument which Landlord or such
Mortgagee may request subordinating, the Lease and all rights of Tenant under
the Lease to any Mortgage, and to all advances made under such mortgage provided
that (i) the holder of any such Mortgage shall execute and deliver to Tenant a
nondisturbance agreement to the effect that, in the event of any foreclosure of
such Mortgage, such holder will not name Tenant as a party defendant to such
foreclosure nor disturb its possession under the Lease, or (ii) any such
Mortgage shall contain provisions substantially to the same effect as those
contained in such a nondisturbance agreement.

     21.8  Limitations on Liability.  Nothing, contained in the foregoing
           ------------------------
Section 21.7 or in any such nondisturbance agreement or nondisturbance provision
shall, however, affect the prior rights of the holder of any Mortgage with
respect to the proceeds of any award in condemnation or of any fire insurance
policies affecting the Building, or impose upon any such holder any liability
(i) for the erection or completion of the Building, or (ii) in the event of
damage or destruction to the Building, or the Demised Premises by fire or other
casualty, for any repairs, replacements, rebuilding or restoration except such
repairs, replacements, rebuilding or restoration as can reasonably be
accomplished from the net proceeds of insurance actually receive by, or made
available to, such holder, or (iii) for any default by Landlord under the Lease
occurring prior to any date upon which such holder shall become Tenant's
Landlord, or (iv) for any credits, offsets or claims against the rent under the
Lease as a result of any acts or omissions of Landlord committed or omitted
prior to such date, or (v) for return of any security deposit or other funds
unless the same shall have been received by such holder, and any such agreement
or provision may so state.

     22.   QUIET ENJOYMENT

     Landlord covenants that if, and so long as, Tenant keeps and performs each
and every covenant, agreement, term, provision and condition herein contained on
the part and on behalf of
<PAGE>

Tenant to be kept and performed, Tenant shall quietly enjoy the Demised Premises
from and against the claims of all persons claiming by, through or under
Landlord subject, nevertheless, to the covenants, agreements, terms, provisions
and conditions of this Lease and to the mortgages, ground leases and/or
underlying leases to which this Lease is subject and subordinate.

     23.   ENTIRE AGREEMENT - WAIVER - SURRENDER

     23.1  Entire Agreement. This Lease and the Exhibits made a part hereof
           ----------------
contain the entire and only agreement between the parties and any and all
statements and representations, written and oral, including previous
correspondence and agreements between the parties hereto are merged herein.
Tenant acknowledges that all representations and statements upon which it relied
in executing, this Lease are contained herein and that Tenant in no way relied
upon any other statements of representations, written or oral. Any executory
agreement hereafter made shall be ineffective to change, modify, discharge or
effect an abandonment of this Lease in whole or in part unless such executory
agreement is in writing and signed by the party against whom enforcement of the
change, modification, discharge or abandonment is sought. Nothing herein shall
prevent the parties from agreeing to amend this Lease and the Exhibits made part
hereof as long as such amendment shall be in writing and shall be duly signed by
both parties.

     23.2  Waiver by Landlord. The failure of Landlord to seek redress for
           ------------------
violation, or to insist upon the strict performance, of any covenant or
condition of this Lease, or any of the Rules and Regulations promulgated
hereunder, shall not prevent a subsequent act, which would have originally
constituted a violation, from having all the force and effect of an original
violation. The receipt by Landlord of rent with knowledge of the breach of any
covenant of this Lease shall not be deemed a waiver of such breach. The failure
of Landlord to enforce any of such Rules and Regulations against Tenant and/or
any other tenant or subtenant in the Building shall not be deemed a waiver of
any such Rules and Regulations. No provisions of this Lease shall be deemed to
have been waived by Landlord unless such waiver be in writing signed by
Landlord. No payment by Tenant or receipt by Landlord of a lesser amount than
the monthly rent herein stipulated shall be deemed to be other than on account
of the stipulated rent, nor shall any endorsement or statement on any check or
any letter accompanying any check or payment as rent be deemed ail accord and
satisfaction, and Landlord may accept such check or payment without prejudice of
Landlord's right to recover the balance of such rent or pursue any other remedy
in this Lease provided.

     23.3  Surrender. No act or thing done by Landlord during the term hereby
           ---------
demised shall be deemed an acceptance of a surrender of the Demised 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 Demised Premises prior to the termination of
this Lease. The delivery of keys to any employee of Landlord or of shall not
operate as a termination of the Lease or a surrender of the Demised Premises. In
the event that Tenant at any time desires to have Landlord underlet the Demised
Premises Tenant's account, Landlord or Landlord's agents are authorized to
receive the keys for such purposes without releasing Tenant from any of the
obligations under this Lease, and Tenant
<PAGE>

hereby relieves Landlord of any liability for loss of or damage to any of
Tenant's effects in connection with such underletting.

     24.   INABILITY TO PERFORM - EXCULPATORY CLAUSE

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

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

25.  BILLS AND NOTICES

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

     All bills and statements for reimbursement or other payments or charges due
from Tenant to Landlord hereunder shall set forth in reasonable detail the
particulars relating thereto and shall be due and payable in full thirty (30)
days, unless herein otherwise provided, after submission thereof by Landlord to
Tenant. Landlord shall, at Tenant's reasonable request, promptly furnish Tenant
with such additional reasonable details relating thereto as Tenant shall
reasonably request. Tenant's failure to make timely payment of any amounts
indicated by such bills and statements, whether for work done by Landlord at
Tenant's request, reimbursement provided for by this Lease or for any other sums
properly owing by Tenant to Landlord, shall be treated as a default in the
payment of Rent, in which event Landlord shall have all rights and remedies
provided in this Lease for the nonpayment of Rent.

26.  PARTIES BOUND - SEIZING OF TITLE

     The covenants, agreements, terms, provisions and conditions of this Lease
shall bind and benefit the successors and assigns of the parties hereto with the
same effect as if mentioned in each instance where a party hereto is named or
referred to, except that no violation of the provisions of Article 14 hereof
shall operate to vest any rights in any successor or assignee of Tenant and that
the provisions of this Article shall not be construed as modifying the
conditions of limitation contained in Article 19 hereof.

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

27.  MISCELLANEOUS

     27.1  Separability. If any provision of this Lease or portion of such
           ------------
provision or the application thereof to any person or circumstance is for any
reason held invalid or unenforceable, the remainder of the Lease (or the
remainder of such provision) and the application thereof to other persons or
circumstances shall not be affected thereby.

     27.2  Captions. The captions are inserted only as a matter of convenience
           --------
and for reference, and in no way define, limit or describe the scope of this
Lease nor the intent of any provision thereof.

     27.3  Broker. Each party represents and warrants that it has not directly
           ------
or indirectly dealt, with respect to the leasing of office space in the
Building, with any broker or had its
<PAGE>

attention called to the Premises or other space to let in the Building, by any
broker other than the Broker(s) (if any) listed in Article 1 whose commission
shall be the responsibility of Landlord. Each party agrees to exonerate and save
harmless and indemnify the other against any claims for a commission by any
other broker, person or firm with whom such party has dealt in connection with
the execution and delivery of this Lease or out of negotiations between Landlord
and Tenant with respect to the leasing of other space in the Building.

     27.4  Governing, Law. This lease is made pursuant to, and shall be governed
           --------------
by, and construed in accordance with, the laws of the Commonwealth of
Massachusetts.

     27.5  Assignment of Rents. With reference to any assignment by Landlord of
           -------------------
its interest in this Lease, or the Rent payable hereunder, conditional in nature
or otherwise, which assignment is made to or held by a bank, trust company,
insurance company or other institutional lender holding a Mortgage on the
Building, Landlord and Tenant agree:

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

           (b)  that, except as aforesaid, such Mortgagee shall be treated as
having assumed the Landlord's obligations thereunder only upon foreclosure of
such Mortgagee's Mortgage and the taking of possession of the Demised Premises
after having given notice of its exercise of the option stated in Article 21
hereof to succeed to the interest of the Landlord under this Lease.

     27.6  Parking. Landlord shall allocate to Tenant the number of non-
           -------
exclusive Parking Spaces indicated in Article 1. Landlord may, pursuant to
Section 15.1, establish Rules and Regulations relative to all parking areas
serving Building tenants and may further engage the services of an independent
contractor to administer and control access to said parking areas. Landlord or
said independent contractor shall impose separate charges for use of said
parking areas, and such charges shall be payable by Tenant as Additional Rent
with respect to Tenant's Parking Spaces. During the initial three (3) years of
the Term of this Lease, the monthly charge for each Parking Space situated in
the garage facility serving the Building shall be One Hundred Forty Dollars
($140). Thereafter, the monthly charge shall be as from time to time established
by Landlord or said independent contractor as the then prevailing monthly
parking charge for the Building. Tenant acknowledges that Landlord has informed
Tenant that Landlord intends to allocate in its tenant leases up to one hundred
twenty-five percent (125%) of the actual parking spaces servicing the Building.
It is further acknowledged and agreed that as a consequence of such over-
allocation of parking spaces there may occasionally occur instances in which the
number of parking spaces actually available to Tenant shall be less than the
Parking Spaces to which Tenant is entitled under this Lease. Landlord shall
incur no liability to Tenant as a consequence of such over-allocation of parking
spaces.
<PAGE>

     27.7  Notice of Lease. Neither party shall record this Lease in any
           ---------------
Registry of Deeds or Registry District.

     27.8  Financial Statements. If requested by Landlord, Tenant shall furnish
           --------------------
to Landlord promptly after they are available to Tenant copies of Tenant's
annual financial statements (audited, if available) and unaudited quarterly
financial statements. It is understood and agreed that Landlord may furnish
copies of such financial statements to its mortgagees.
<PAGE>

     IN WITNESS WHEREOF, Landlord and Tenant have caused this instrument to be
executed under seal, all as of the day and year first above written.

                    RIVERFRONT OFFICE PARK ASSOCIATES II LIMITED PARTNERSHIP

                                        By:  DARVEL REALTY TRUST
                                               Managing General Partner

                                        By:  /s/ Michael P. Sullivan
                                             -----------------------------------
                                             Michael P. Sullivan, Vice President

                                        MAINSPRING COMMUNICATIONS, INC.

                                        By:  /s/ John M. Connolly
                                             -----------------------------------
                                             John M. Connolly, President
<PAGE>

                                   EXHIBIT A
                                   ---------

                                  FLOOR PLAN
                                  ----------
<PAGE>

                                   EXHIBIT B
                                   ---------

                              DESCRIPTION OF LAND
                              -------------------

     A certain parcel of land in the City of Cambridge, Middlesex County,
Massachusetts, bounded and described as follows:

     SOUTHWESTERLY            at the intersection of Main Street and First
                              Street, by four lines measuring 44.72 feet, 129.49
                              feet, 24.15 feet, and 41.16 feet, respectively;

     SOUTHERLY                by Main Street by a line measuring 404.86 feet;

     WESTERLY                 by Lot 1, by a line measuring 154.28 feet; and

     NORTHERLY                by the Broad Canal, 594.60 feet.

     Said parcel is shown as Lot 2 on a "Subdivision Plan of Land in Cambridge,
Mass. (Middlesex County)", dated April 24, 1981, and revised September 4, 1981,
drawn by Boston Survey Consultants, and prepared for Darvel Realty Trust,
recorded with Middlesex Southern District Registry of Deeds in Book 14412. Page
199.
<PAGE>

                                   EXHIBIT D
                                   ---------

                     PROCEDURE FOR ALLOCATION OF COSTS OF
                        ELECTRIC POWER USAGE BY TENANTS

     1.   Main electric service to the Building will be provided by the local
utility company to a single main meter. All charges by the utility will be read
from this meter and billed to and paid by Landlord at rates established by the
utility company.

     (Separate electric service from the utility company directly to tenants may
be made available to retail tenants on the ground floor if Landlord determines
this to be appropriate to the tenancy involved.)

     2.   In order to allocate charges for electric service fairly among tenants
in relation to the relative amounts of electricity used by each tenant,
additional meters (known as "check meters") will be installed by Landlord for
each tenant to measure all electricity provided for lights and power to that
tenant. This shall not, however, include the following, which shall be wired
from the main building service and not through the check meters: stairwell and
emergency lights; elevators; heat pumps and HVAC in the Building; exterior
lighting; and all main building mechanical systems (common areas on each floor,
including the elevator lobby, corridors, and bathrooms, will have service
through the check meters on each floor) (the "Basic Building Electricity") and
which shall be separately metered.

     3.   Additional check meters may be installed by Landlord where necessary
to assure measurement of all electric service to tenant areas (e.g., in the case
of separate dedicated circuits to computer rooms, cafeterias, or other special
purpose facilities). Ground floor tenant space will be check metered if it is
not separately metered. In addition, further modification to the number and
location of check meters may be made by Landlord if required to improve the
quality of information obtained thereby.

     4.   Landlord will cause the check meters to be read monthly by its
employees and will perform an analysis of the information for the purpose of
determining an equitable allocation of the costs of electric service among the
tenants in the Building in relation to the respective amounts of usage of
electricity by those tenants.

     5.   Each tenant's allocable share ("Tenant's Allocable Electricity Cost"),
shall be determined by Landlord on the following basis:

     a.   The total kilowatt hour usage for the period under evaluation shall be
          established for each check meter and also for the Building as a whole
          by a reading of the main building meter for that period.

     b.   The cost of the total amount of electricity supplied for usage by
          tenants during the period (exclusive of the Base Building Electricity)
          (herein called "Tenant
<PAGE>

          Electricity") shall be determined by multiplying the total cost of
          electricity as invoiced by the utility company for the same period by
          a fraction, the numerator of which is the total amount of kilowatt
          hour usage as measured by all of the Tenant Electricity check meters
          in the Building and the denominator of which is the total amount of
          kilowatt hour usage for the Building as measured by the main building
          electric meter.

     c.   Tenant's Allocable Electricity Cost for the period shall be determined
          by multiplying the total costs of Tenant Electricity by a fraction,
          the numerator of which is the kilowatt hour usage of Tenant
          Electricity by said tenant (calculated as the sum of kilowatt hour
          usage during the period measured by all check meters serving its
          premises) and the denominator of which is the total kilowatt hour
          usage of Tenant Electricity for the same period.

     d.   Where part or all of the rentable area on a floor has been occupied by
          a tenant for less than all of the period for which said Tenant's
          Allocable Electricity Cost is being calculated, appropriate and
          equitable modifications shall be made to the allocation formula so
          that each tenant's allocable share of costs equitably reflects its
          period of occupancy, provided that in no event shall the total of all
          costs as allocated to tenants be less than the total cost of Tenant
          Electricity for said period.

     6.   All costs of Base Building Electricity to Landlord shall be treated as
part of the Operating Costs of the Building for purposes of determining the
allocation of those costs.
<PAGE>

                                   EXHIBIT E
                                   ---------

                             RULES AND REGULATIONS
                             ---------------------

     1.   The sidewalks, entrances, passages, courts, elevators, vestibules,
stairways, corridors or halls of the Building shall not be obstructed or
encumbered or used for any purpose other than ingress and egress to and from the
premises demised to any tenant or occupant.

     2.   No awnings or other projections shall be attached to the outside walls
or windows of the Building without the prior consent of Landlord. No curtains,
blinds, shades, or screens shall be attached or hung in, or used in connection
with, any window or door of the premises demised to any tenant or occupant,
without the prior consent of Landlord. Such awnings, projections, curtains,
blinds, shades, screens, or other fixtures must be of a quality type, design and
color, and attached in a manner, approved by Landlord.

     3.   No sign, advertisement, object, notice or other lettering shall be
exhibited, inscribed, painted or affixed on any part of the outside or inside of
the premises demised to any tenant or occupant of the Building without the prior
written consent of Landlord. Interior signs on doors and directory tables, if
any, shall be of a size, color and style approved by Landlord.

     4.   The sashes, sash doors, skylights, windows, and doors that reflect or
admit light and air into the halls, passageways or other public places in the
Building shall not be covered or obstructed, nor shall any bottles, parcels, or
other articles be placed or stored upon on any window sills.

     5.   No show cases or other articles of any kind shall be put in front of
or affixed to any part of the exterior of the Building, nor placed in the halls,
corridors, vestibules or other parts of the Building.

     6.   The water and wash closets and other plumbing fixtures shall not be
used for any purposes other than those for which they were constructed, and no
sweepings, rubbish, rags, or other substances shall be thrown therein.

     7.   No tenant or occupant shall mark, paint, drill into, or in any way
deface any part of the Building or the premises demised to such tenant or
occupant. No boring, cutting or stringing of wires shall be permitted, except
with the prior consent of the Landlord, and as Landlord tiny direct. No tenant
or occupant shall install any resilient tile or similar floor covering in the
premises demised to such tenant or occupant except in manner approved by
Landlord.

     8.   No bicycles, vehicles or animals of any kind shall be brought into or
kept in or about the premises demised to any tenant. Bicycles may be stored in
racks, if any, furnished for such purpose by Landlord in a common area of the
Building. No cooking shall be done or permitted in the Building by any tenant
without the approval of Landlord. No tenant shall cause
<PAGE>

or permit any unusual or objectionable odors to emanate from the premises
demised to such tenant.

     9.   Without the prior consent of Landlord, no space in the Building shall
be used for manufacturing, or for the sale of merchandise, goods or property of
any kind at auction.

     10.  No tenant shall make, or permit to be made, any unseemly or disturbing
noises or disturb or interfere with other tenants or occupants of the Building
or neighboring buildings or premises, whether by the use of any musical
instrument, radio, television set or other audio device, unmusical noise,
whistling, singing, or in any other way. Nothing shall be thrown out of any
doors or windows.

     11.  Each tenant must, upon the termination of its tenancy, restore to
Landlord all keys, either furnished to, or otherwise procured by, such tenant,
including without limitation, all parking pass keys, Building, keys, office keys
and keys to storage areas and toilet rooms.

     12.  All removals from the Building, or the carrying in or out of the
Building or the premises demised to any tenant, of any safes, freight,
furniture, or bulky matter of any description must take place at such time and
in such manner as Landlord or its agents may determine, from time to time.
Landlord reserves the right to inspect all freight to be brought into the
Building and to exclude from the Building all freight which violates any of the
Building Rules or the provisions of such tenant's lease.

     13.  No tenant shall use or occupy, or permit any portion of the premises
demised to such tenant to be used or occupied, as an office for a public
stenographer or typist, or to a barber or manicure shop, or as an employment
bureau. No tenant or occupant shall engage or pay any employees in the Building,
except those actually working for such tenant or occupant in the Building, nor
advertise for laborers giving an address at the Building.

     14.  No tenant or occupant shall purchase spring water, ice, food,
beverage, lighting maintenance, cleaning towels or other like service, from any
company or person not approved by Landlord. such approval not unreasonably to be
withheld.

     15.  Landlord shall have the right to prohibit any advertising by any
tenant or occupant which, in Landlord's opinion, tends to impair the reputation
of the Building or its desirability as a building for offices, and upon notice
from Landlord, such tenant or occupant shall refrain from or discontinue such
advertising.

     16.  Landlord reserves the right to exclude from the Building, between the
hours of 6:00 p.m. and 8:00 a.m. on Business Days and otherwise at all hours,
all persons who do not present a pass to the building signed by the Landlord.
Landlord will furnish passes to persons for whom any tenant requests such
passes. Each tenant shall be responsible for all persons for whom it, requests
such passes and shall be liable to Landlord for all wrongful acts of such
persons.
<PAGE>

     17.  Each tenant, before closing and leaving the premises demised to such
tenant at any time, shall see that all entrance doors are locked and windows
closed.

     18.  Each tenant shall, at its expense, provide artificial light in the
premises demised to such tenant for Landlord's agents, contractors, and
employees while performing janitorial or other cleaning services and making
repairs or alterations in said premises.

     19.  No premises shall be used, or permitted to be used, for lodging in or
sleeping, or for any immoral or illegal purpose.

     20.  There shall not be used in the Building, either by any tenant or
occupant or by their agents or contractors, in the delivery or receipt of
merchandise, freight or other matter, any hand trucks or other means of
conveyance, except those equipped with rubber tires, rubber side guards and such
other safeguards as Landlord may require.

     21.  Canvassing, soliciting and peddling in the Building are prohibited and
each tenant and occupant shall cooperate in seeking their prevention.

     22.  If the premises demised to any tenant become infested with vermin,
such tenant, at its sole cost and expense, shall cause its premises to be
exterminated from time to time, to the satisfaction of Landlord and shall employ
such exterminators therefor as shall be approved by Landlord.

     23.  No premises shall be used, or permitted to be used, at any time,
without the prior approval of Landlord, as a store for the sale or display of
goods, wares or merchandise of any kind, or is restaurant, shop, booth,
bootblack or other stand, or for the conduct of any business or occupation which
predominantly involves direct patronage of the general public in the premises
demised to such tenant, or for manufacturing or for other similar purposes.

     24.  No tenant shall move, or permit to be moved, into or out of the
Building or the premises demised to such tenant, any heavy or bulky matter,
without the specific prior written approval of Landlord. If any such matter
requires special handing, only a person holding a Master Rigger's License shall
be employed to perform such special handling. No tenant shall place, or permit
to be placed on any part of the floor or floors of the premises demised to such
tenant, a load exceeding the floor load per square foot which such floor was
designed to carry and which is allowed by law. Landlord reserves the right to
prescribe the weight and position of safes and other heavy matter, which must be
placed so as to distribute the weight.

     25.  The requirements of tenants will be attended to only upon application
at the office of the Building. Building employees shall not be required to
perform, and shall not be requested by any tenant or occupant to perform any
work outside of their regular duties, unless under specific instructions from
the office of the managing agent of the Building.

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