Document:

<PAGE>
                                                                    Exhibit 10.1

                               EXHIBIT 1, SHEET 1
                      Building No. 1400, One Kendall Square
                            Cambridge, Massachusetts
                                (the "Building")

Execution Date:  June 8, 2005
                 ------------

Tenant:          Idenix Pharmaceuticals, Inc.
                 ----------------------------
                                (name)

                 a Delaware corporation
                 ----------------------
                                (description of business organization)

                 60 Hampshire Street, Cambridge, Massachusetts 02139
                 ---------------------------------------------------
                                (principal place of business - mailing address)

Landlord:        One Kendall Square Associates, LLC, a Delaware limited
                 liability company. Mailing address: c/o Lincoln Property
                 Company, 101 Arch Street, Boston, Massachusetts 02110

Building:        Building No. 1400 in One Kendall Square in the City of
                 Cambridge, Middlesex County, Commonwealth of Massachusetts.

Art. 2

                       Premises: Three (3) areas on the first (1st) floor of
                 the Building ("First Floor Premises"), the fourth (4th) floor
                 premises of the Building ("Fourth Floor Premises"), fifth
                 (5th) floor of the Building ("Fifth Floor Premises"), and the
                 penthouse of the Building ("Penthouse Premises") substantially
                 as shown on Lease Plan, Exhibit 2, Sheets 1, 2 and 3. The
                 First Floor Premises, the Fourth Floor Premises, and the Fifth
                 Floor Premises are each sometimes hereinafter referred to as a
                 "Portion of the Premises".

Art. 3.1         Term Commencement Date:  See Article 3.1

Art. 3.2         Termination Date:  Four (4) years and six (6) months after the
                                    Rent Commencement Date (or, if there is more
                                    than one Rent Commencement Date, four (4)
                                    years and six (6) months after the last Rent
                                    Commencement Date to occur

Art. 4.3         Final Plans Date:  Not applicable

Art. 5           Use of Premises:   General business offices and biotechnology
                                    research and development, including as a
                                    BL-3 laboratory, provided that use of the
                                    premises as a BL-3 laboratory is subject to
                                    the following conditions and understandings:
                                    (i) such use shall only be permitted if
                                    Landlord determines either that: (x) there
                                    are adequate facilities available in the
                                    Building which can support such use, or (y)
                                    the Building can accommodate the
                                    installation and construction of such
                                    facilities, at Tenant's cost and expense,
                                    (ii) Tenant obtains all governmental
                                    approvals necessary to permit such use of
                                    the premises, (iii) Tenant performs all work
                                    necessary for such laboratory use in
                                    accordance with the provisions of the Lease
                                    (including, without limitation, and at
                                    Tenant's sole cost and expense, and (iv)
                                    Tenant acknowledges that Landlord has made
                                    no representation to Tenant that such use is
                                    either permitted or possible.
<PAGE>
Art. 6          Yearly Rent:        $ 821,542.50
                                    ------------
                Monthly Payment:    $  68,461.88
                                    ------------

                Tenant's obligation to pay Yearly Rent with respect to each
                Portion of the premises commences as of the Rent Commencement
                Date in respect of such Portion of the premises. The date as of
                which the Rent Commencement Date in respect of the entirety of
                the Premises first occurs is sometimes hereinafter referred to
                as the Full Rent Commencement Date. If the Rent Commencement
                Dates in respect of all Portions of the premises do not occur on
                the same date, then the Yearly Rent payable by Tenant in respect
                of each Portion of the Premises during the period between the
                Rent Commencement Date in respect of such Portion of the
                premises and the Full Rent Commencement Date shall be based upon
                a Yearly Rent rental rate of $22.50 per square foot of Total
                Rentable Area of such Portion of the premises.

Art. 7          Total Rentable Area:   36,514 square feet, comprised of:

                                       First Floor Premises:   4,692 square feet
                                       Fourth Floor Premises: 19,206 square feet
                                       Fifth Floor Premises:  11,502 square feet
                                       Penthouse Premises:     1,113 square feet
                                       -----------------------------------------
                                       Total:                 36,513 square feet

                Total Rentable Area of Building No.1400: 133,298 square feet
                Total Rentable Area of Complex:          650,681 square feet

Art. 8.         Subject to Article 8.1 of the Lease: (i) electric current will
                be furnished by Landlord to Tenant, and (ii) Tenant shall,
                commencing as of the Term Commencement Date, pay to Landlord,
                as additional rent, electricity rent ("Electricity Rent") at
                the same time and in the same manner as Yearly Rent is paid
                under the Lease, in the amount of $63,897.75 per annum (i.e.,
                $5,324.81 per month) (i.e., $1.75 per square foot of Total
                Rentable Area per year).

Art. 9          Operating and Taxes:
                      Building Operating Costs Base:  The actual amount of
                                                      Building Operating Costs
                                                      for calendar year 2005

                      Common Operating Costs Base:    The actual amount of
                                                      Common Operating Costs for
                                                      calendar year 2005

                      Common Tax Base:                The actual amount of
                                                      Common Taxes payable
                                                      during fiscal/tax year
                                                      2006 (i.e., July 1, 2005 -
                                                      June 30, 2006)

                      Building Tax Base:              The actual amount of
                                                      Building Taxes payable
                                                      during fiscal/tax year
                                                      2006 (i.e., July 1, 2005 -
                                                      June 30, 2006)

                      Tenant's Proportionate Shares:

                      Building Share:       27.39%
                      Common Area Share:     5.61%
<PAGE>
Art. 29.3       Brokers:  Richard Barry Joyce & Partners, LLC and Lincoln
                          Property Company

Art. 29.5       Arbitration:  Massachusetts; Superior Court

                Exhibit Dates:  Lease Plan, Exhibit 2, dated June 8, 2005

Art. 29.12:     Letter of Credit Amount:  $410,771.25, subject to reduction in
                                          accordance with Article 29.12
<PAGE>

THIS INDENTURE OF LEASE made and entered into on the Execution Date as stated in
Exhibit 1 and between the Landlord and the Tenant named in Exhibit 1.

Landlord does hereby demise and lease to Tenant, and Tenant does hereby hire and
take from Landlord, the premises hereinafter mentioned and described
(hereinafter referred to as "premises"), upon and subject to the covenants,
agreements, terms, provisions and conditions of this Lease for the term
hereinafter stated. Each reference in this Lease to any of the terms and titles
contained in any Exhibit attached to this Lease shall be deemed and construed to
incorporate the data stated under that term or title in such Exhibit.

1.    BACKGROUND

      Reference is made to the following:

      1.1 The premises are currently leased (together with other premises) to
another tenant in the Complex, Genzyme Corporation ("Genzyme") pursuant to a
lease ("Genzyme Lease") by and between Genzyme and Landlord.

      1.2 The term of the Genzyme Lease in respect of the premises terminates as
of the date ("Genzyme Termination Date") which is the earlier of: (x) July 24,
2005, or (y) the date fourteen (14) days after Landlord gives Genzyme a written
termination notice ("Genzyme Termination Notice").

      1.3 Landlord hereby agrees to give the Genzyme Termination Notice
immediately upon execution and delivery of this Lease by both parties.

2.    DESCRIPTION OF DEMISED PREMISES

      2.1 DEMISED PREMISES. The premises are that portion of the Building as
described in Exhibit 1 (as the same may from time to time be constituted after
changes therein, additions thereto and eliminations therefrom pursuant to rights
of Landlord hereinafter reserved) and is hereinafter referred to as "Building",
substantially as shown hatched or outlined on the Lease Plan (Exhibit 2) hereto
attached and incorporated by reference as a part hereof.

      2.2 APPURTENANT RIGHTS. Tenant shall have, as appurtenant to the premises,
rights to use in common, with others entitled thereto, subject to reasonable
rules from time to time made by Landlord of which Tenant is given notice; (a)
the common lobbies, hallways, stairways and elevators of the Building, serving
the premises in common with others, (b) common walkways necessary for access to
the Building, and (c) if the premises include less than the entire rentable area
of any floor, the common toilets and other common facilities of such floor; and
no other appurtenant rights or easements.

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

3.    TERM OF LEASE

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

            (a) The "Term Commencement Date" with respect to each Portion of the
premises shall be defined as the day after the Genzyme Termination Date, as
defined in Article 1.2, provided however, that, Tenant is obtains the written
agreement from Genzyme to permit Tenant to commence occupancy of a Portion of
the Premises prior to the Genzyme Termination Date, then the Term Commencement
Date with respect to such Portion of the premises shall be the day that Tenant
first commences to use such Portion of the Premises for any purpose (including,
without limitation, commencement of Tenant Work or the installation Tenant's
property in such Portion of the Premises).

            (b) The "Occupancy Date" with respect to each Portion of the
Premises shall be defined as the earlier of: (i) the Outside Occupancy Date, as
hereinafter defined, or (ii) the date that Tenant first commences to use the
premises, or any portion thereof, for business purposes.

                                      -1-
<PAGE>

            (c) The "Outside Occupancy Date" is the date sixty (60) days after
the last Term Commencement Date to occur; provided however, that if Landlord's
Work is not substantially complete on or before the Outside Occupancy Date, then
the Outside Occupancy Date shall be the date that Landlord's Work is
substantially complete.

            (d) The "Rent Commencement Date" with respect to each Portion of the
premises shall be the date thirty (30) days after the Occupancy Date with
respect to such Portion of the premises.

            (e) "Complex" shall be defined as all of the Building, the other
buildings, and the Common Areas serving such buildings, all located on the land
("Land") shown outlined on Exhibit 4.

            (f) "Common Areas" shall be defined as the common walkways,
accessways, and parking facilities located on the Land, as the same may be
changed, from time to time.

            (g) "Landlord's Work" shall be defined as the work described on
Exhibit 2A.

            (h) "Tenant's Work" shall be defined as the work to be performed by
Tenant in preparing the premises for Tenant's occupancy.

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

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

4.    CONDITION OF PREMISES - LANDLORD'S WORK - LANDLORD'S CONTRIBUTION

      4.1   CONDITION OF PREMISES.

      (a) Notwithstanding anything to the contrary herein contained, except as
otherwise expressly set forth in this Lease, Tenant shall take the premises
"as-is", in the condition in which the premises are in as of the Term
Commencement Date, without any obligation on the part of Landlord to prepare or
construct the premises for Tenant's occupancy and without any warranty or
representation by Landlord as to the condition of the premises or the Building,
Tenant shall have the right to re- use any materials, finishes and equipment
which exist in the premises as of the date that the premises are delivered to
Tenant as part of Tenant's Work. Landlord represents to Tenant that, as of the
Execution Date of this Lease, the HVAC system serving the premises ("HVAC
System") is in operating condition. If, on or before the date sixty (60) days
after the Occupancy Date, Tenant gives written notice to Landlord setting forth
with specificity any breach of the foregoing representation, then, Landlord
shall, at no cost to Tenant, perform such work as is necessary to bring the HVAC
system into compliance with the foregoing representation. The foregoing
provisions of Article 4.1(a) shall be Tenant's sole remedy for any breach of the
foregoing representation by Landlord.

      (b) Subject to delay by causes beyond the reasonable control of Landlord
or caused by the action or inaction of Tenant, Landlord shall use reasonable
speed to substantially complete Landlord's Work on or before the date
("Estimated Occupancy Date") sixty (60) days after the Term Commencement Date.
Landlord's failure to substantially complete Landlord's Work on or before the
Estimated Occupancy Date shall in no way affect the validity of this Lease or
the obligations of Tenant hereunder nor shall the same be construed in any way
to extend the term of this Lease, except that the Outside Occupancy Date shall
be delayed in the event of such failure by Landlord. If Landlord fails to
substantially complete Landlord's Work on or before the Estimated Occupancy
Date, then, except as set forth in Article 4.1(c), Tenant shall not have any
claim against Landlord, and Landlord shall have no liability to Tenant, by
reason thereof.

                                      -2-
<PAGE>

      (c) If Landlord has not substantially completed Landlord's Work on or
before the Outside Completion Date (defined below), then, and as Tenant's sole
remedy (other than the extension of the Outside Occupancy Date and the Rent
Commencement Date, as provided in the definition of each of such terms), Tenant
shall be entitled to liquidated damages equal to the product of $2,108.94
multiplied by each day between the date that Landlord substantially completes
Landlord's Work and the Outside Completion Date. Such liquidated damages shall
be effected by allowing Tenant a rent credit against the first installment(s) of
Yearly Rent and other charges due under the Lease. The "Outside Completion Date"
shall mean the date which is sixty (60) days after the Term Commencement Date,
provided however, that the Outside Completion Date shall be extended by the
number of days which Landlord is delayed in the performance of Landlord's Work
by reason of delays or default of Tenant or Tenant's agents, employees or
contractors, and the Outside Completion Date shall also be extended by the
lesser of: (i) thirty (30) days, or (ii) the number of days that Landlord is
delayed in the performance of Landlord's Work by reason of other causes beyond
Landlord's reasonable control.

      (d) Landlord's Work shall be deemed to be substantially complete when the
items of Landlord's Work are complete other than minor and insubstantial details
of construction. Notwithstanding the foregoing, in the event that Landlord's
Work is delayed by reason of Tenant Delays, then Landlord's Work shall be deemed
to be substantially complete as of the date that Landlord's Work would have been
substantially complete but for such Tenant Delay. "Tenant Delays" shall be
defined as any delay and/or default on the part of Tenant or its contractors.
Landlord's certificate of substantial completion, as hereinabove stated, given
in good faith, or of any other facts pertinent to this Article 4.1(c) shall be
deemed conclusive of the statements therein contained and binding upon Tenant,
unless, within five (5) business days after Tenant's receipt of such
certificate, Tenant gives written notice to Landlord, setting forth with
specificity its objections to such certificate. Any of item of Landlord's Work
which is not fully completed at the time of substantial completion for such item
of Landlord's Work shall thereafter be so completed with reasonable diligence by
Landlord.

      4.2   LANDLORD'S CONTRIBUTION.

      (a) Landlord shall, in the manner hereinafter set forth, contribute up to
Eight Hundred Five Thousand Eight Hundred and Forty-One and 91/100 ($805,841.91)
Dollars ("Landlord's Contribution") towards: (i) the Hard Costs and Soft Costs
incurred by Tenant in connection with Tenant's Work; provided however, that no
more than $182,565.00 of Landlord's Contribution may be applied towards Soft
Costs. "Hard Costs" shall be defined as the cost of leasehold improvements which
are part of Tenant's Work, including, without limitation, materials, supplies,
overhead, and general conditions cost. "Soft Costs" shall be defined as design
and engineering fees, the cost of installing wiring and cabling in the premises,
the cost of moving Tenant's personal property and equipment into the premises,
and the cost of furniture installed in the premises.

      (b) Provided that Tenant is not in default of its obligations under the
Lease at the time that Tenant requests any requisition on account of Landlord's
Contribution, Landlord shall pay the cost of the work shown on each requisition
(as hereinafter defined) submitted by Tenant to Landlord within thirty (30) days
of submission thereof by Tenant to Landlord. For the purposes hereof, a
"requisition" shall mean written documentation showing in reasonable detail the
costs of the improvements then installed by Tenant in the premises. Each
requisition shall be accompanied by evidence reasonably satisfactory to Landlord
that all work covered by previous requisitions has been fully paid by Tenant.
Landlord shall have the right, upon reasonable advance notice to Tenant, to
inspect Tenant's books and records relating to each requisition in order to
verify the amount thereof. Tenant shall submit requisition(s) no more often than
monthly.

      (c) Notwithstanding anything to the contrary herein contained:

      (i) Landlord shall have no obligation to advance funds on account of
Landlord's Contribution unless and until Landlord has received the requisition
in question, together with certifications from Tenant's architect, certifying
that the work shown on the requisition has been performed in accordance with
applicable law and in accordance with Tenant's approved plans.

      (ii) Except with respect to work and/or materials previously paid for by
Tenant, as evidenced by paid invoices provided to Landlord, Landlord shall have
the right to have Landlord's Contribution paid to both Tenant and Tenant's
contractor(s) and vendor(s) jointly, or directly to Tenant's contractor if
Landlord has reason to believe there are or may be outstanding claims by such
contractor(s) or vendor(s).

      (iii) Landlord shall have no obligation to pay Landlord's Contribution in
respect of any requisition submitted after the date eight (8) months after the
Occupancy Date.

      (iv) Tenant shall not be entitled to any unused portion of Landlord's
Contribution.

      (d) Except for Landlord's Contribution, Tenant shall bear all other costs
of Tenant's Work.

                                      -3-
<PAGE>

      4.3 TENANT'S WORK. Tenant's Work shall be performed in accordance with the
provisions of the Lease (including, without limitation, Articles 12 and 13
hereof). Landlord shall have no liability or responsibility for any claim,
injury or damage alleged to have been caused by the particular materials,
whether building standard or non-building standard, selected by Tenant in
connection with Tenant's Work.

      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 with respect to Landlord's Work unless not later than the end of
the second calendar month next beginning after the Rent Commencement Date Tenant
shall give Landlord written notice specifying the respects in which Landlord has
not performed any such obligation.

5.    USE OF PREMISES

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

      5.2 PROHIBITED USES. Notwithstanding any other provision of this Lease,
Tenant shall not use, or suffer or permit the use or occupancy of, or suffer or
permit anything to be done in or anything to be brought into or kept in or about
the premises or the Building or any part thereof (including, without limitation,
any materials appliances or equipment used in the construction or other
preparation of the premises and furniture and carpeting): (i) which would
violate any of the covenants, agreements, terms, provisions and conditions of
this Lease or otherwise applicable to or binding upon the premises; (ii) for any
unlawful purposes or in any unlawful manner; (iii) which, in the reasonable
judgment of Landlord shall in any way (a) impair the appearance of the Building;
or (b) impair, interfere with or otherwise diminish the quality of any of the
Building services or the proper and economic heating, cleaning, ventilating, air
conditioning or other servicing of the Building; or premises, or with the use or
occupancy of any of the other areas of the Building, or occasion discomfort,
inconvenience or annoyance, or injury or damage to any occupants of the premises
or other tenants or occupants of the Building; or (iv) which is inconsistent
with the maintenance of the Building as an office building of the first class in
the quality of its maintenance, use, or occupancy. Tenant shall not install or
use any electrical or other equipment of any kind which, in the reasonable
judgment of Landlord, might cause any such impairment, interference, discomfort,
inconvenience, annoyance or injury.

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

      5.4 VACANCY BY TENANT. If Tenant shall abandon or vacate the premises for
a period of no less than one hundred twenty (120) days, then Landlord shall have
the right to terminate this Lease upon written notice to Tenant. Provided that
Tenant is in compliance with its obligations under the Lease, such termination
shall not be deemed to be based upon Tenant's default.

6.    RENT

      During the term of this Lease the Yearly Rent and other charges, at the
rate stated in Exhibit 1, shall be payable by Tenant to Landlord by monthly
payments, as stated in Exhibit 1, in advance and without demand on the first day
of each month for and in respect of such month. The rent and other charges
reserved and covenanted to be paid under this Lease shall commence on the Term
Commencement Date, except that Yearly Rent to be paid under this Lease shall
commence on the Rent Commencement Date. Notwithstanding the provisions of the
next preceding sentence, Tenant shall pay the first monthly installment of rent
on the execution of this Lease. If, by reason of any provisions of this Lease,
the rent reserved hereunder shall commence or terminate on any day other than
the first day of a calendar month, the rent for such calendar month shall be
prorated. The rent shall be payable to Landlord or, if Landlord shall so direct
in writing, to Landlord's agent or nominee, in lawful money of the United States
which shall be legal tender

                                      -4-
<PAGE>

for payment of all debts and dues, public and private, at the time of payment,
at the office of the Landlord or such place as Landlord may designate, and the
rent and other charges in all circumstances shall be payable without any setoff
or deduction whatsoever. Rental and any other sums due hereunder not paid on or
before the date due shall bear interest for each month or fraction thereof from
the due date until paid computed at the annual rate of five percentage points
over the so-called prime rate then currently from time to time charged to its
most favored corporate customers by the largest national bank (N.A.) located in
Boston, Massachusetts, or at any applicable lesser maximum legally permissible
rate for debts of this nature.

7.    RENTABLE AREA

      Total Rentable Area of the premises, the Building and the Complex are
agreed to be the amounts set forth in Exhibit 1.

8.    SERVICES FURNISHED BY LANDLORD

      8.1   ELECTRIC CURRENT.

      (a) Subject to the provisions of this Article 8.1(a), as stated in Exhibit
1: (i) Landlord will furnish to Tenant, as an incident of this Lease, electric
current for the operation of lighting fixtures and the 120-volt electrical
outlets initially installed in the premises for the operation of Tenant's normal
office fixtures and equipment, but excluding any high energy consumption
equipment, and (ii) Tenant shall commencing as of the Term Commencement Date and
continuing thereafter throughout the term of the Lease, pay Electricity Rent to
Landlord.

      (b) Landlord, at any time, at its option and upon not less than thirty
(30) days' prior written notice to Tenant, may discontinue such furnishing of
electric current to the premises; and in such case Tenant shall contract with
the company supplying electric current for the purchase and obtaining by Tenant
of electric current directly from such company. In the event Tenant itself
contracts for electricity with the supplier, either initially or pursuant to
Landlord's option as above stated, Landlord shall (i) permit its risers,
conduits and feeders to the extent available, suitable and safely capable, to be
used for the purpose of enabling Tenant to purchase and obtain electric current
directly from such company, (ii) without cost or charge to Tenant, make such
alterations and additions to the electrical equipment and/or appliances in the
Building as such company shall specify for the purpose of enabling Tenant to
purchase and obtain electric current directly from such company, and (iii) at
Landlord's expense, furnish and install in or near the premises any necessary
metering equipment used in connection with measuring Tenant's consumption of
electric current and Tenant, at Tenant's expense, shall maintain and keep in
repair such metering equipment. In the event that Landlord shall exercise the
option set forth in this Subparagraph 8.1(b), then Tenant shall have no further
obligation to pay Electricity Rent to Landlord after the date Landlord
discontinues such furnishing of electric current.

      (c) If Landlord exercises is rights, pursuant to Article 8.1(b), to
require Tenant to contract with the company supplying electric current for the
purchase and obtaining by Tenant of electric current directly from such company,
Tenant shall contract with such company and shall pay all charges for such
electric current directly to such company promptly when due.

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

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

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

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

                                      -5-
<PAGE>

unreasonably withheld, and will promptly advise Landlord of any other alteration
or addition to such electrical equipment and/or appliances.

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

      8.3 ELEVATORS, HEAT AND CLEANING. Landlord at its expense shall: (i)
provide necessary automatic elevator facilities on Mondays through Fridays,
excepting legal holidays, from 8:00 a.m. to 6:00 p.m. and on Saturdays,
excepting legal holidays, from 8:00 a.m. to 1:00 p.m. (called "business days")
and have one elevator in operation available for Tenant's use, non-exclusively,
together with others having business in the Building, at all other times; (ii)
furnish heat (substantially equivalent to that being furnished in comparably
aged similarly equipped office buildings in the same city) to the premises
during the normal heating season on business days; and (iii) cause the common
areas of the Building to be cleaned on business days (i.e., Monday through
Friday) in a manner consistent with cleaning standards generally prevailing in
the office buildings in the City of Cambridge.

      8.4 AIR CONDITIONING. Landlord shall through the air conditioning
equipment of the Building furnish to and distribute in the premises air
conditioning as normal seasonal changes may require on business days during the
hours as aforesaid in Article 8.3 when air conditioning may reasonably be
required for the comfortable occupancy of the premises by Tenant. Tenant agrees
to lower and close the blinds or drapes when necessary because of the sun's
position, whenever the air conditioning system is in operation, and to cooperate
fully with Landlord with regard to, and to abide by all the reasonable
regulations and requirements which Landlord may prescribe for the proper
functioning and protection of the air conditioning system. The air conditioning
system referred to in this Article 8.4 shall be capable of maintaining a
temperature range that is reasonably standard for buildings of similar class,
size, age and location.

      8.5 ADDITIONAL HEAT AND AIR CONDITIONING SERVICES.

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

            (b) Tenant will pay to Landlord a reasonable charge for any such
additional heat or air conditioning service required by Tenant. Landlord hereby
represents to Tenant that, as of the Execution Date, the charge for additional
heat or air conditioning service is $75.00 per hour; provided that if more than
one tenant of the Building requests additional heating or air conditioning
service for the same time period, then the charge for such service shall be
shared equally among the tenants requesting such service for such time period.

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

            (a) by Landlord at Tenant's expense and Tenant shall reimburse
Landlord in such an amount as will compensate it for the cost incurred by it in
operating, maintaining, repairing and replacing, if necessary, such additional
air conditioning equipment; or

            (b) by Tenant, subject to Landlord's prior approval of Tenant's
plans and specifications for such work. In such event: (i) such equipment shall
be maintained, repaired and replaced by Tenant at Tenant's sole cost and
expense, and (ii) throughout the term of this Lease, Tenant shall, at Tenant's
sole cost and expense, purchase and maintain a service contract for such
equipment from a service provider approved by Landlord. Tenant shall obtain
Landlord's prior written approval of both the form of service contract and of
the service provider.

                                      -6-
<PAGE>

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

      8.8   INTERRUPTION OR CURTAILMENT OF SERVICES.

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

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

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

      8.9 ENERGY CONSERVATION. Notwithstanding anything to the contrary in this
Article 8 or in this Lease contained, Landlord may institute, and Tenant shall
comply with, such policies, programs and measures as may be necessary, required,
or expedient for the conservation and/or preservation of energy or energy
services, or as may be necessary or required to comply with applicable codes,
rules regulations or standards.

      8.10 MISCELLANEOUS. Other than air conditioning, all services provided by
Landlord to Tenant are based upon an assumed maximum premises population of one
person per two hundred (200) square feet of Total Rentable Area, which limit
Tenant shall in no event exceed.

9.    ESCALATION

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

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

            (b) "Tenant's Proportionate Building Share" shall be the figure as
stated in Exhibit 1. Tenant's Proportionate Building Share is the ratio of the
Total Rentable Area of the premises to the aggregate Total Rentable Area of the
Building.

            (c) "Tenant's Proportionate Common Area Share" shall initially be
the figure as stated in Exhibit 1. Tenant's Proportionate Common Area Share is
the ratio of the Total Rentable Area of the premises to the aggregate Total
Rentable Area, from time to time, of all buildings within the Complex which have
been completed and for which a certificate of occupancy has been issued. As
additional buildings are completed within the Complex, Tenant's Proportionate
Common Area Share shall be adjusted to equal the then current ratio of the Total
Rentable Area of the premises to the aggregate Total Rentable Area within the
Complex which is then completed and as to which a certificate of occupancy is
issued.

                                      -7-
<PAGE>

            (d) "Taxes" shall mean the real estate taxes and other taxes, levies
and assessments imposed upon the Building and the Common Areas of the Complex
and upon any personal property of Landlord used in the operation thereof, or
Landlord's interest in the Building, the Common Areas, or such personal
property; charges, fees and assessments for transit, housing, police, fire or
other governmental services or purported benefits to the Building and/or the
Common Areas; service or user payments in lieu of taxes; and any and all other
taxes, levies, betterments, assessments and charges arising from the ownership,
leasing, operating, use or occupancy of the Building, the Common Areas or based
upon rentals derived therefrom, which are or shall be imposed by National,
State, Municipal or other authorities. As of the Execution Date, "Taxes" shall
not include any franchise, rental, income or profit tax, capital levy or excise,
provided, however, that any of the same and any other tax, excise, fee, levy,
charge or assessment, however described, that may in the future be levied or
assessed as a substitute for or an addition to, in whole or in part, any tax,
levy or assessment which would otherwise constitute "Taxes," whether or not now
customary or in the contemplation of the parties on the Execution Date of this
Lease, shall constitute "Taxes," but only to the extent calculated as if the
Complex is the only real estate owned by Landlord. "Taxes" shall also include
expenses of tax abatement or other proceedings contesting assessments or levies.
The parties acknowledge that, as of the Execution Date, Taxes are based upon
several separate tax bills affecting the Complex. Taxes shall be allocated by
Landlord, in Landlord's reasonable judgment, among the Building (the portion of
Taxes allocable to the Building being referred to herein as "Building Taxes"),
the other buildings of the Complex, and the Common Areas (the portion of Taxes
allocable to the Common Areas being referred to herein as "Common Area Taxes").

            (e) "Tax Period" shall be any fiscal/tax period in respect of which
Taxes are due and payable to the appropriate governmental taxing authority, any
portion of which period occurs during the term of this Lease, the first such
Period being the one in which the Term Commencement Date occurs.

            (f) "Operating Costs":

                  (1) Definition of Operating Costs. "Operating Costs" shall
            mean all costs incurred and expenditures of whatever nature made by
            Landlord in the operation and management, for repair and
            replacements, cleaning and maintenance of the Building, the Complex,
            and the Common Areas of the Complex including, without limitation,
            vehicular and pedestrian passageways related to the Complex, related
            equipment, facilities and appurtenances, elevators, cooling and
            heating equipment. In the event that Landlord or Landlord's managers
            or agents perform services for the benefit of the Complex off-site
            which would otherwise be performed on-site (e.g., accounting), the
            cost of such services shall be reasonably allocated among the
            properties benefiting from such service and shall be included in
            Operating Costs. Operating Costs shall include, without limitation,
            those categories of "Specifically Included Operating Costs," as set
            forth below, but shall not include "Excluded Costs," as hereinafter
            defined.

                  (2) Definition of Excluded Costs. "Excluded Costs" shall be
            defined as mortgage charges, brokerage commissions, salaries of
            executives and owners not directly employed in the
            management/operation of the Complex, the cost of work done by
            Landlord for the Tenant for which Tenant pays a separate charge, or
            for a particular tenant for which Landlord has the right to be
            reimbursed by such Tenant, any costs incurred by Landlord solely in
            connection with the operation of the Garage, any costs incurred by
            Landlord solely in connection with the operation of another Building
            in the Complex, costs of compliance with the ADA to the extent that
            such costs are excluded from Operating Costs pursuant to Article
            17.7(b) of the Lease, and, subject to Subparagraph (3) below, such
            portion of expenditures as are not properly chargeable against
            income.

                  (3) Capital Expenditures.

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

                        (ii) New Capital Items. If a new capital item is
                  acquired which does not replace another capital item which was
                  worn out, has become obsolete, etc., then there shall be
                  included in Operating Costs for each Operating Year in which
                  and after such capital expenditure is made the Annual
                  Charge-Off of such capital expenditure. Notwithstanding
                  anything to the contrary herein contained, with respect to a
                  new (i.e.

                                      -8-
<PAGE>

                  as opposed to replacement) capital expenditure, such capital
                  expenditure shall be included in Operating Costs only if:

                        1. the new capital item being acquired is required by
                           law, ordinance or regulation which first becomes
                           effective and applicable to the Complex after the
                           Execution Date of this Lease, or

                        2. The new capital item is reasonably projected to
                           reduce Operating Costs (taking into account the
                           Annual Change-Off included in Operating Costs on
                           account of such capital item).

                        (iii) Annual Charge-Off. "Annual Charge-Off" shall be
                  defined as the annual amount of principal and interest
                  payments which would be required to repay a loan ("Capital
                  Loan") in equal monthly installments over the Useful Life, as
                  hereinafter defined, of the capital item in question on a
                  direct reduction basis at an annual interest rate equal to the
                  Capital Interest Rate, as hereinafter defined, where the
                  initial principal balance is the cost of the capital item in
                  question. Notwithstanding the foregoing, if Landlord
                  reasonably concludes on the basis of engineering estimates
                  that a particular capital expenditure will effect savings in
                  Building operating expenses including, without limitation,
                  energy-related costs, and that such projected savings will, on
                  an annual basis ("Projected Annual Savings"), exceed the
                  Annual Charge-Off of such capital expenditure computed as
                  aforesaid, then and in such events, the Annual Charge-Off
                  shall be increased to an amount equal to the Projected Annual
                  Savings; and in such circumstances, the increased Annual
                  Charge-Off (in the amount of the Projected Annual Savings)
                  shall be made for such period of time as it would take to
                  fully amortize the cost of the capital item in question,
                  together with interest thereon at the Capital Interest Rate as
                  aforesaid, in equal monthly payments, each in the amount of
                  one-twelfth (1/12th) of the Projected Annual Savings, with
                  such payments being applied first to interest and the balance
                  to principal.

                        (iv) Useful Life. "Useful Life" shall be reasonably
                  determined by Landlord in accordance with generally accepted
                  accounting principles and practices in effect at the time of
                  acquisition of the capital item.

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

                  (4) Specifically Included Categories of Operating Costs.
            Operating Costs shall include, but not be limited to, the following:

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

                  Water: All charges and rates connected with water supplied to
            the Building and related sewer use charges.

                  Heat and Air Conditioning: All charges connected with heat and
            air conditioning supplied to the Building.

                  Wages: Wages and cost of all employee benefits of all
            employees of the Landlord and/or Landlord's managing agent who are
            employed in, about or on account of the Building, provided however,
            that Operating Costs shall not include wages or costs with respect
            to any employee above the level of general manager.

                  Cleaning: The cost of labor and material for cleaning the
            Building, surrounding areaways and windows in the Building.

                  Elevator Maintenance: All expenses for or on account of the
            upkeep and maintenance of all elevators in the Building.

                                      -9-
<PAGE>

                  Management Fee: The cost of professional management of the
            Building at a rate not to exceed four (4%) of gross income.

                  Administrative Costs: The cost of office expense, including,
            without limitation, rent, business supplies and equipment.

                  Electricity: The cost of all electric current for the
            operation of any machine, appliance or device used for the operation
            of the premises and the Building, including the cost of electric
            current for the elevators, lights, air conditioning and heating, but
            not including electric current which is paid for directly to the
            utility by the user/tenant in the Building. (If and so long as
            Tenant is billed directly by the electric utility for its own
            consumption as determined by its separate meter, or billed directly
            by Landlord as determined by a check meter, then Operating Costs
            shall include only Building and public area electric current
            consumption and not any demised premises electric current
            consumption. Wherever separate metering is unlawful, prohibited by
            utility company regulation or tariff or is otherwise impracticable,
            relevant consumption figures for the purposes of this Article 9
            shall be determined by fair and reasonable allocations and
            engineering estimates made by Landlord. Furthermore, if and to the
            extent that the Operating-Costs-in-the-Base-Year figure shall
            include any component representing the cost to the Landlord of
            electric current supplied to any tenant's premises under so-called
            "rent-inclusion" lease arrangements, then if such cost is eliminated
            from Operating Costs in an Operating Year in accordance with the
            foregoing provisions, the figure for Operating Costs in the Base
            Year for the purposes of this Article 9 shall likewise be reduced by
            the amount for such cost component.)

                  Insurance, etc.: Fire, casualty, liability, rent loss and such
            other insurance as may from time to time be required by lending
            institutions on first-class office buildings in Cambridge,
            Massachusetts and all other expenses customarily incurred in
            connection with the operation and maintenance of first-class office
            buildings in Cambridge, Massachusetts including, without limitation,
            insurance deductible amounts and rental costs associated with the
            Building's management office.

            (5) Definitions of Building Operating Costs and Common Area
            Operating Costs. "Building Operating Costs" shall be defined as the
            amount of Operating Costs allocable to the Building in any Operating
            Year. "Common Area Operating Costs" shall be defined as the amount
            of Operating Costs allocable to the Common Areas in any Operating
            Year. All Operating Costs incurred by Landlord in respect of the
            Complex shall be allocated, in Landlord's reasonable judgment, among
            the Building, the other buildings of the Complex, and the Common
            Areas.

      9.2 TAX EXCESS. Commencing as of the Rent Commencement Date and continuing
thereafter with respect to each Tax Year occurring during the term of the Lease,
Tenant shall pay to Landlord, with respect to any Tax Period, the sum of: (x)
Tenant's Proportionate Building Share of the amount (if any) by which Building
Taxes for such Tax Period exceeds the Building Tax Base, plus (y) Tenant's
Proportionate Common Share of the amount (if any) by which Common Area Taxes for
such Tax Period exceeds the Common Area Tax Base, such amount being hereinafter
referred to as "Tax Excess". Tax Excess shall be due when billed by Landlord. In
implementation and not in limitation of the foregoing, Tenant shall remit to
Landlord pro rata monthly installments on account of projected Tax Excess,
calculated by Landlord on the basis of the most recent Tax data or budget
available. If the total of such monthly remittances on account of any Tax Period
is greater than the actual Tax Excess for such Tax Period, Tenant may credit the
difference against the next installment of rental or other charges due to
Landlord hereunder. If the total of such remittances is less than the actual Tax
Excess for such Tax Period, Tenant shall pay the difference to Landlord when
billed therefor.

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

      9.3 OPERATING EXPENSE EXCESS. Commencing as of the Rent Commencement Date
and continuing thereafter with respect to each Operating Year occurring during
the term of the Lease, Tenant shall pay to Landlord, with respect to any
Operating Year, the sum of: (x) Tenant's Proportionate Building Share of the
amount (if any) by which Building Operating Costs for such Operating Year
exceeds the Building Operating Costs Base, plus (y) Tenant's Proportionate
Common Share of the amount (if any) by which Common Operating Costs for such
Operating Year exceeds the Common Operating Costs Base, such amount being
hereinafter referred to as "Operating Expense Excess." Operating Expense Excess
shall be due when billed by Landlord. In implementation and not in limitation of
the foregoing, Tenant shall remit to Landlord pro rata monthly installments on
account of projected Operating

                                      -10-
<PAGE>

Expense Excess, calculated by Landlord on the basis of the most recent Operating
Costs data or budget available. If the total of such monthly remittances on
account of any Operating Year is greater than the actual Operating Expense
Excess for such Operating Year, Tenant may credit the difference against the
next installment of rent or other charges due to Landlord hereunder. If the
total of such remittances is less than actual Operating Expense Excess for such
Operating Year, Tenant shall pay the difference to Landlord when billed
therefor.

      9.3A TENANT'S AUDIT RIGHT. Subject to the provisions of this paragraph,
Tenant shall have the right, at Tenant's cost and expense, to examine all
documentation and calculations prepared in the determination of Operating
Expense Excess:

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

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

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

      4.    Such examination may be made only by a national recognized
            independent certified public accounting firm approved by Landlord.
            Without limiting Landlord's approval rights, Landlord may withhold
            its approval of any examiner of Tenant who is being paid by Tenant
            on a contingent fee basis.

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

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

      9.5 EFFECT OF TAKING. In the event of any taking of the Building or the
land upon which it stands under circumstances whereby this Lease shall not
terminate under the provisions of Article 20 then, Tenant's Proportionate
Building Share and Tenant's Proportionate Common Area Share shall be adjusted
appropriately to reflect the proportion of the premises and/or the Building
remaining after such taking.

      9.6 SURVIVAL. Any obligations under this Article 9 which shall not have
been paid at the expiration or sooner termination of the term of this Lease
shall survive such expiration and shall be paid when and as the amount of same
shall be determined to be due.

10.   CHANGES OR ALTERATIONS BY LANDLORD

      Landlord reserves the right, exercisable by itself or its nominee, at any
time and from time to time without the same constituting an actual or
constructive eviction and without incurring any liability to Tenant therefor or
otherwise affecting Tenant's obligations under this Lease, to make such changes,
alterations, additions, improvements, repairs or replacements in or to: (i) the
Building (including the premises) and the fixtures and equipment thereof, (ii)
the street entrances, halls, passages, elevators, escalators, and stairways of
the Building, and (iii) the Common Areas, and facilities located therein, as
Landlord 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 and/or the
Common Areas, provided, however, that there be no unreasonable obstruction of
the right of access to, or unreasonable interference with the use and enjoyment
of, the premises by Tenant. Nothing contained in this Article 10 shall be deemed
to relieve Tenant of any duty, obligation or liability of Tenant with respect to
making any repair, replacement or improvement or complying with any law, order
or requirement of any governmental or other authority. Landlord reserves the
right to adopt and at any time and from time to time to change the name or
address of the Building. Neither this Lease nor any use by Tenant shall give
Tenant any right or easement for the use of any door, passage, concourse,
walkway or parking area within the Building or in the Common Areas, and the use
of such doors, passages, concourses, walkways, parking areas and such
conveniences may be regulated or discontinued at any time and from time to time
by Landlord without notice to Tenant and without affecting the obligation of
Tenant hereunder or incurring any liability to Tenant therefor, provided,
however, that there be no unreasonable obstruction of the right of access to, or
unreasonable interference with the use of the premises by Tenant.

                                      -11-
<PAGE>

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

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

      All fixtures, equipment, improvements and appurtenances attached to or
built into the premises prior to or during the term, whether by Landlord at its
expense or at the expense of Tenant (either or both) or by Tenant shall be and
remain part of the premises and shall not be removed by Tenant during or at the
end of the term unless Landlord otherwise elects to require Tenant to remove
such fixtures, equipment, improvements and appurtenances, in accordance with
Articles 12 and/or 22 of the Lease. All electric, telephone, telegraph,
communication, radio, plumbing, heating and sprinkling systems, fixtures and
outlets, vaults, paneling, molding, shelving, radiator enclosures, cork, rubber,
linoleum and composition floors, ventilating, silencing, air conditioning and
cooling equipment, shall be deemed to be included in such fixtures, equipment,
improvements and appurtenances, whether or not attached to or built into the
premises. Where not built into the premises, all removable electric fixtures,
carpets, drinking or tap water facilities, furniture, or trade fixtures or
business equipment or Tenant's inventory or stock in trade shall not be deemed
to be included in such fixtures, equipment, improvements and appurtenances and
may be, and upon the request of Landlord will be, removed by Tenant upon the
condition that such removal shall not materially damage the premises or the
Building and that the cost of repairing any damage to the premises or the
Building arising from installation or such removal shall be paid by Tenant.

12.   ALTERATIONS AND IMPROVEMENTS BY TENANT

      (a) Tenant shall make no alterations, decorations, installations,
removals, additions or improvements in or to the premises without Landlord's
prior written consent made by contractors or mechanics approved by Landlord. No
installations or work shall be undertaken or begun by Tenant until: (i) Landlord
has approved written plans and specifications and a time schedule for such work;
(ii) Tenant has made provision for either written waivers of liens from all
contractors, laborers and suppliers of materials for such installations or work,
the filing of lien bonds on behalf of such contractors, laborers and suppliers,
or other appropriate protective measures approved by Landlord; and (iii) Tenant
has procured appropriate surety payment and performance bonds. No material
amendments or additions to such plans and specifications shall be made without
the prior written consent of Landlord.

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

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

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

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

      (c) Landlord's consent and approval required under this Article 12 shall
not be unreasonably withheld. Landlord's approval is solely given for the
benefit of Landlord and neither Tenant nor any third party shall have the right
to rely upon Landlord's approval of Tenant's plans for any purpose whatsoever.
Without limiting the foregoing, Tenant shall be responsible for all elements of
the design of Tenant's plans (including, without limitation, compliance with
law, functionality of design, the structural integrity of the design, the
configuration of the premises and the placement of Tenant's furniture,
appliances and equipment), and Landlord's approval of Tenant's plans shall in no
event relieve Tenant of the responsibility for such design. Landlord shall have
no liability or responsibility for any claim, injury or damage alleged to have
been caused by the particular materials, whether building standard or
non-building standard, appliances or equipment selected by Tenant in connection
with any work performed by or on behalf of Tenant in the premises including,
without limitation, furniture, carpeting, copiers, laser printers, computers and
refrigerators.

      (d) Any such work, alterations, decorations, installations, removals,
additions and improvements shall be done at Tenant's sole expense and at such
times and in such manner as Landlord may from time to time designate.

      (e) If Tenant shall make any alterations, decorations, installations,
removals, additions or improvements then Landlord may elect to require the
Tenant at the expiration or sooner termination of the term of this Lease to
restore the premises to substantially the same condition as existed at the Term
Commencement Date. Landlord agrees to make such election at the time that
Landlord

                                      -12-
<PAGE>

approves Tenant's plans for any such alterations, etc., if Tenant requests in
writing that Landlord make such election at the time that Tenant requests
Landlord's approval of such alterations, etc.

      (f) Tenant shall pay, as an additional charge, the entire increase in real
estate taxes on the Building which shall result from or be attributable to any
alteration, addition or improvement to the premises made by or for the account
of Tenant.

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

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

            (a) Tenant agrees that it will not, either directly or indirectly,
use any contractors and/or materials if their use will create any difficulty,
whether in the nature of a labor dispute or otherwise, with other contractors
and/or labor engaged by Tenant or Landlord or others in the construction,
maintenance and/or operation of the Building or any part thereof, but Tenant
shall not be required to engage union labor if Tenant is able, nonetheless, to
satisfy the requirements of this Article 13(a).

            (b) In no event shall any material or equipment be incorporated in
or added to the premises, so as to become a fixture or otherwise a part of the
Building, in connection with any such alteration, decoration, installation,
addition or improvement which is subject to any lien, charge, mortgage or other
encumbrance of any kind whatsoever or is subject to any security interest or any
form of title retention agreement. No installations or work shall be undertaken
or begun by Tenant until (i) Tenant has made provision for written waiver of
liens from all contractors, laborers and suppliers of materials for such
installations or work, and taken other appropriate protective measures approved
by Landlord; and (ii) Tenant has procured appropriate surety payment and
performance bonds which shall name Landlord as an additional obligee and has
filed lien bond(s) (in jurisdictions where available) on behalf of such
contractors, laborers and suppliers. Any mechanic's lien filed against the
premises or the Building for work claimed to have been done for, or materials
claimed to have been furnished to, Tenant shall be discharged by Tenant within
ten (10) days thereafter, at Tenant's expense by filing the bond required by law
or otherwise. If Tenant fails so to discharge any lien, Landlord may do so at
Tenant's expense and Tenant shall reimburse Landlord for any expense or cost
incurred by Landlord in so doing within fifteen (15) days after rendition of a
bill therefor.

            (c) All installations or work done by Tenant shall be at its own
expense and shall at all times comply with (i) laws, rules, orders and
regulations of governmental authorities having jurisdiction thereof; (ii)
orders, rules and regulations of any Board of Fire Underwriters, or any other
body hereafter constituted exercising similar functions, and governing insurance
rating bureaus; (iii) Rules and Regulations of Landlord; and (iv) plans and
specifications prepared by and at the expense of Tenant theretofore submitted to
and approved by Landlord.

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

14.   REPAIRS BY TENANT--FLOOR LOAD

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

                                      -13-
<PAGE>

other property, or by misuse by, or neglect, or improper conduct of, Tenant or
Tenant's servants, employees, agents, contractors, or licensees.

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

15.   INSURANCE, INDEMNIFICATION, EXONERATION AND EXCULPATION

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

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

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

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

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

            (c) On account of or based upon (including monies due on account of)
any work or thing whatsoever done (other than by Landlord or its contractors, or
agents or employees of either) on the 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 premises.

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

                                      -14-
<PAGE>

      15.4 PROPERTY OF TENANT. In addition to and not in limitation of the
foregoing, Tenant covenants and agrees that, to the maximum extent permitted by
law, all merchandise, furniture, fixtures and property of every kind, nature and
description related or arising out of Tenant's leasehold estate hereunder, which
may be in or upon the premises or Building, in the public corridors, or on the
sidewalks, areaways and approaches adjacent thereto, shall be at the sole risk
and hazard of Tenant, and that if the whole or any part thereof shall be
damaged, destroyed, stolen or removed from any cause or reason whatsoever no
part of said damage or loss shall be charged to, or borne by, Landlord.

      15.5 BURSTING OF PIPES, ETC. Landlord shall not be liable for any injury
or damage to persons or property resulting from fire, explosion, falling
plaster, steam, gas, air contaminants or emissions, electricity, electrical or
electronic emanations or disturbance, water, rain or snow or leaks from any part
of the Building or from the pipes, appliances, equipment or plumbing works or
from the roof, street or sub-surface or from any other place or caused by
dampness, vandalism, malicious mischief or by any other cause of whatever
nature, unless caused by or due to the negligence of Landlord, its agents,
servants or employees, and then only after (i) notice to Landlord of the
condition claimed to constitute negligence and (ii) the expiration of a
reasonable time after such notice has been received by Landlord without Landlord
having taken all reasonable and practicable means to cure or correct such
condition, where notice and an opportunity to cure are appropriate (i.e., where
Tenant has an opportunity to know or should have known of such condition
sufficiently in advance of the occurrence of any such injury or damage resulting
therefrom as would have enabled Landlord to prevent such damage or loss had
Tenant notified Landlord of such condition); and pending such cure or correction
by Landlord, Tenant shall take all reasonably prudent temporary measures and
safeguards to prevent any injury, loss or damage to persons or property. In no
event shall Landlord be liable for any loss, the risk of which is covered by
Tenant's insurance or is required to be so covered by this Lease; nor shall
Landlord or its agents be liable for any such damage caused by other tenants or
persons in the Building or caused by operations in construction of any private,
public, or quasi-public work; nor shall Landlord be liable for any latent defect
in the premises or in the Building.

      15.6  REPAIRS AND ALTERATIONS--NO DIMINUTION OF RENTAL VALUE.

      (a) Except as otherwise provided in Article 18, there shall be no
allowance to Tenant for diminution of rental value and no liability on the part
of Landlord by reason of inconvenience, annoyance or injury to Tenant arising
from any repairs, alterations, additions, replacements or improvements made by
Landlord, or any related work, Tenant or others in or to any portion of the
Building or premises or any property adjoining the Building, or in or to
fixtures, appurtenances, or equipment thereof, or for failure of Landlord or
others to make any repairs, alterations, additions or improvements in or to any
portion of the Building, or of the premises, or in or to the fixtures,
appurtenances or equipment thereof.

      (b) Notwithstanding anything to the contrary in this Lease contained, if
due to any such repairs, alterations, replacements, or improvements made by
Landlord or if due to Landlord's failure to make any repairs, alterations, or
improvements required to be made by Landlord, any portion of the premises
becomes untenantable so that for the Premises Untenantability Cure Period, as
hereinafter defined, the continued operation in the ordinary course of Tenant's
business is materially adversely affected, then, provided that Tenant ceases to
use the affected portion of the premises during the entirety of the Premises
Untenantability Cure Period by reason of such untenantability, and that such
untenantability and Landlord's inability to cure such condition is not caused by
the fault or neglect of Tenant or Tenant's agents, employees or contractors,
Yearly Rent, Operating Expense Excess and Tax Excess shall thereafter be abated
in proportion to such untenantability until the day such condition is completely
corrected. For the purposes hereof, the "Premises Untenantability Cure Period"
shall be defined as five (5) consecutive business days after Landlord's receipt
of written notice from Tenant of the condition causing untenantability in the
premises, provided however, that the Premises Untenantability Cure Period shall
be ten (10) consecutive business days after Landlord's receipt of written notice
from Tenant of such condition causing untenantability in the premises if either
the condition was caused by causes beyond Landlord's control or Landlord is
unable to cure such condition as the result of causes beyond Landlord's control.

      (c) The provisions of Paragraph (b) of this Article 15.6 shall not apply
in the event of untenantability caused by fire or other casualty, or taking (see
Articles 18 and 20).

16.   ASSIGNMENT, MORTGAGING AND SUBLETTING

      (a) Tenant covenants and agrees that neither this Lease nor the term and
estate hereby granted, nor any interest herein or therein, will be assigned,
mortgaged, pledged, encumbered or otherwise transferred, voluntarily, by
operation of law or otherwise, and that neither the premises, nor any part
thereof will be encumbered in any manner by reason of any act or omission on the
part of Tenant, or used or occupied, or permitted to be used or occupied, or
utilized for desk space or for mailing privileges, by anyone other than Tenant,
or for any use or purpose other than as stated in Exhibit 1, or be sublet, or
offered or advertised for subletting. Notwithstanding the foregoing, it is
hereby expressly understood and agreed however, if Tenant is a corporation, that
the assignment or transfer of this Lease, and the term and estate hereby
granted, to any corporation into which Tenant is merged or with which Tenant is
consolidated which corporation shall have a net worth at least equal to that of
Tenant immediately prior to such merger or

                                      -15-
<PAGE>

consolidation (such corporation being hereinafter called "Assignee"), shall not
be deemed to be prohibited hereby if, and upon the express condition that
Assignee and Tenant shall promptly execute, acknowledge and deliver to Landlord
an agreement ("Assumption Agreement") in form and substance satisfactory to
Landlord whereby Assignee shall agree to be independently bound by and upon all
the covenants, agreements, terms, provisions and conditions set forth in this
Lease on the part of Tenant to be performed, and whereby Assignee shall
expressly agree that the provisions of this Article 16 shall, notwithstanding
such assignment or transfer, continue to be binding upon it with respect to all
future assignments and transfers; provided however, that if, by reason of such a
merger or consolidation, the Tenant does not survive and the Assignee is deemed
to have assumed all of Tenant's obligations under the Lease by operation of law,
Tenant and the Assignee deliver to Landlord reasonable evidence of such merger
and consolidation in lieu of delivering to Landlord an Assumption Agreement.

      (b) Notwithstanding anything to the contrary in the Lease contained:

      (1) Tenant shall, prior to offering or advertising the premises, or any
portion thereof, for sublease or assignment to any person or entity or than an
Assignee, as defined in Article 16A, or an Affiliated Entity, as defined in
Article 16D, give Landlord a Recapture Offer, as hereinafter defined.

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

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

            (ii) Identifies the affected portion of the premises ("Recapture
      Premises").

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

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

      (3) Landlord shall have a period of time equal to the applicable
Acceptance Period, as hereinafter defined, to accept a Recapture Offer by
written notice to Tenant within such Acceptance Period. The "Acceptance Period"
with respect to any proposed sublease where the size of the Recapture Premise is
less than 10,000 square feet of Total Rentable Area shall be have thirty (30)
days after Landlord receives the Recapture Offer, and the "Acceptance Period"
with respect to any proposed sublease where the size of the Recapture Premises
is 10,000 square feet of Total Rentable Area or more shall be forty-five (45)
days after Landlord receives the Recapture Offer. If Landlord does not timely
give written notice to Tenant accepting a Recapture Offer, then Landlord agrees
that it will not unreasonably withhold or delay its consent to a sublease of the
Recapture Premises for the Recapture Period, or an assignment of Tenant's
interest in the Lease, as the case may be, to a Qualified Transferee, as
hereinafter defined.

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

            (i) is financially responsible and of good reputation;

            (ii) is engaged in a business, the functional aspects of which, with
      respect to the premises, are similar to the use of other premises made by
      other office space tenants in the Building; and

            (iii) such Qualified Transferee desires is not a Restricted
      Occupant, as hereinafter defined.

      (5) For the purposes hereof, a "Restricted Occupant" shall be defined as
any tenant or subtenant of premises in the Complex ("Occupant") unless such
Occupant satisfies all three of the following criteria:

            (i) Such Occupant desires to sublease the Recapture Premises for
      expansion purposes only; and

            (ii) Such Occupant's occupancy of the Recapture Premises will not,
      either directly or indirectly, cause a vacancy in the premises which such
      occupant then occupies in the Complex; and

                                      -16-
<PAGE>

            (iii) Such Occupant's need, as to the size of premises and length of
      term, cannot then (i.e., at the time that Tenant requests Landlord's
      consent to such Occupant) be satisfied by Landlord.

      (6) Notwithstanding anything to the contrary in this Article 16(b)
contained:

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

            (ii) If Tenant does not enter into a sublease with a subtenant (or
      an assignment to an assignee, as the case may be) approved by Landlord, as
      aforesaid, on or before the date which is one hundred eighty (180) days
      after the earlier of: (x) the expiration of the applicable Acceptance
      Period, or (y) the date that Landlord notifies Tenant that Landlord will
      not accept Tenant's offer to terminate or suspend the Lease, then Landlord
      shall have the right arbitrarily to withhold its consent to any subletting
      or assignment proposed to be entered into by Tenant after the expiration
      of said one hundred eighty (180) day period unless Tenant again offers, in
      accordance with this Article 16(b), either to terminate or to suspend the
      Lease in respect of the portion of the premises proposed to be sublet (or
      in respect of the entirety of the premises in the event of a proposed
      assignment, as the case may be). If Tenant shall make any subsequent
      offers to terminate or suspend the Lease pursuant to this Article 16(b),
      any such subsequent offers shall be treated in all respects as if it is
      Tenant's first offer to suspend or terminate the Lease pursuant to this
      Article 16(b), provided that the period of time Landlord shall have in
      which to accept or reject such subsequent offer shall be fifteen (15)
      days.

      (7) Notwithstanding anything to the contrary herein contained, Tenant
shall have no right, under this Article 16(b), prior to the date one (1) year
after the Occupancy Date. Without limiting the foregoing, Tenant shall have no
right to give Landlord a Recapture Offer prior to the date one (1) year after
the Occupancy Date.

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

      (c) Notwithstanding anything to the contrary herein contained, Tenant
shall have the right, without obtaining Landlord's consent and without giving
Landlord a Recapture Offer, to assign its interest in this Lease and to sublease
the premises, or any portion thereof, to an Affiliated Entity, as hereinafter
defined, so long as such entity remains in such relationship to Tenant, and
provided that prior to or simultaneously with such assignment or sublease, such
Affiliated Entity executes and delivers to Landlord an Assumption Agreement, as
hereinabove defined. For the purposes hereof, an "Affiliated Entity" shall be
defined as any entity which is controlled by, is under common control with, or
which controls Tenant. For the purposes hereof, control shall mean the direct or
indirect ownership of more than fifty (50%) percent of the beneficial interest
of the entity in question.

      (d) In the event of an assignment of this Lease or a sublease of the
premises or any portion thereof to anyone other than an Assignee, as defined in
Article 16(a), or an Affiliated Entity, as defined in Article 16(c), Tenant
shall pay to Landlord fifty (50%) percent of any Net Sublease Profits (as
defined below), payable in accordance with the following. In the case of an
assignment of this Lease, "Net Sublease Profit": (1) shall be defined as a lump
sum in the amount (if any) by which any consideration paid by the assignee in
consideration of or as an inducement to Tenant to make said assignment exceeds
the reasonable attorneys' fees, construction costs and brokerage fees incurred
by Tenant in order to effect such assignment (collectively, "Sublease
Expenses"), and (2) be payable concurrently with the payment to be made by the
assignee to Tenant. In the case of a sublease, "Net Sublease Profit": (3) shall
be defined as a monthly amount equal to the amount by which the sublease rent
and other charges payable by the subtenant to Tenant under the sublease exceed
the sum of the rent and other charges payable under this Lease for the premises
or allocable to the sublet portion thereof, plus a monthly amount equal to the
Sublease Expenses divided by the number of months in the term of the sublease,
and (4) shall be payable on a monthly basis concurrently with the subtenant's
payment of rent to Tenant under the sublease, but only to the extent such
sublease rents are actually received by Tenant.

      (e) If Tenant is an individual who uses and/or occupies the premises with
partners, or if Tenant is a partnership, then:

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

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

                                      -17-
<PAGE>

without regard to the time when such new partner is admitted to partnership or
when any obligations under any such covenants, etc., accrue.

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

17.   MISCELLANEOUS COVENANTS

      Tenant covenants and agrees as follows:

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

      17.2 ACCESS TO PREMISES--SHORING. Tenant shall: (i) permit Landlord to
erect, use and maintain pipes, ducts and conduits in and through the premises,
provided the same do not materially reduce the floor area or materially
adversely affect the appearance thereof or materially interfere with Tenant's
use of the premises; (ii) upon prior twenty-four (24) hour oral notice (except
that no notice shall be required in emergency situations), permit Landlord and
any mortgagee of the Building or the Building and land or of the interest of
Landlord therein, and any lessor under any ground or underlying lease, and their
representatives, to have reasonable access to and to enter upon the premises at
all reasonable hours for the purposes of inspection or of making repairs,
replacements or improvements in or to the premises or the Building or equipment
(including, without limitation, sanitary, electrical, heating, air conditioning
or other systems) or of complying with all laws, orders and requirements of
governmental or other authority or of exercising any right reserved to Landlord
by this Lease (including the right during the progress of any such repairs,
replacements or improvements or while performing work and furnishing materials
in connection with compliance with any such laws, orders or requirements to take
upon or through, or to keep and store within, the premises all necessary
materials, tools and equipment), provided that Tenant shall have the right to
provide appropriate escorts to such persons in order to enable Tenant to
preserve its security and confidentiality; and (iii) permit Landlord, at
reasonable times, and upon reasonable written notice to Tenant to show the
premises during ordinary business hours to any existing or prospective
mortgagee, ground lessor, space lessee (within the last nine (9) months of the
term of the Lease), purchaser, or assignee of any mortgage, of the Building or
of the Building and the land or of the interest of Landlord therein, and during
the period of 12 months next preceding the Termination Date to any person
contemplating the leasing of the premises or any part thereof. If, during the
last month of the term, Tenant shall have removed all or substantially all of
Tenant's property therefrom, Landlord may immediately enter and alter, renovate
and redecorate the premises, without elimination or abatement of rent, or
incurring liability to Tenant for any compensation, and such acts shall have no
effect upon this Lease. If Tenant shall not be personally present to open and
permit an entry into the premises at any time when for any reason an entry
therein shall be permissible, Landlord or Landlord's agents may enter the same
by a master key, or, in an emergency, by force if necessary, without rendering
Landlord or such agents liable therefor (if during such entry Landlord or
Landlord's agents shall accord reasonable care to Tenant's property), and
without in any manner affecting the obligations and covenants of this Lease.
Provided that Landlord shall incur no additional expense thereby, Landlord shall
exercise its rights of access to the premises permitted under any of the terms
and provisions of this Lease in such manner as to minimize to the extent
practicable interference with Tenant's use and occupation of the premises. If an
excavation shall be made upon land adjacent to the premises or shall be
authorized to be made, Tenant shall afford to the person causing or authorized
to cause such excavation, license to enter upon the premises for the purpose of
doing such work as said person shall deem necessary to preserve the Building
from injury or damage and to support the same by proper foundations without any
claims for damages or indemnity against Landlord, or diminution or abatement of
rent.

                                      -18-
<PAGE>

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

      17.4 SIGNS, BLINDS AND DRAPES. Except as set forth in this Article 17.4,
Tenant shall have no right to install any signs in any part of the Building
other than interior signage which is not visible from either the exterior of the
Building or the common areas. Notwithstanding the foregoing, subject to the
provisions of this Article 17.4, Tenant shall have the right, at Tenant's sole
cost and expense, to install the signage shown on Exhibit 4. Such signage shall
be subject to all applicable local building codes and receipt of required
permits from the City of Cambridge, Massachusetts. Such signage shall be subject
to the prior written approval of Landlord (which approval shall not be
unreasonably withheld). Tenant shall maintain such signage in good condition, at
Tenant's sole cost and expense, and Tenant shall, on or before the expiration or
prior termination of the term of the Lease, remove such signage and repair any
damage to the Building caused by the installation or removal of such signage. No
signs or blinds may be put on or in any window or elsewhere if visible from the
exterior of the Building, nor may the building standard drapes or blinds be
removed by Tenant. Tenant may hang its own drapes, provided that they shall not
in any way interfere with the building standard drapery or blinds or be visible
from the exterior of the Building and that such drapes are so hung and installed
that when drawn, the building standard drapery or blinds are automatically also
drawn. Any signs or lettering in the public corridors or on the doors shall
conform to Landlord's building standard design. Neither Landlord's name, nor the
name of the Building or any Center, Office Park or other Park of which the
Building is a part, or the name of any other structure erected therein shall be
used without Landlord's consent in any advertising material (except on business
stationery or as an address in advertising matter), nor shall any such name, as
aforesaid, be used in any undignified, confusing, detrimental or misleading
manner.

      17.5 ESTOPPEL CERTIFICATE. Tenant shall at any time and from time to time
upon not less than ten (10) business days' prior notice by Landlord to Tenant,
execute, acknowledge and deliver to Landlord a statement in writing certifying
that this Lease is unmodified and in full force and effect (or if there have
been modifications, that the same is in full force and effect as modified and
stating the modifications), and the dates to which the Yearly Rent and other
charges have been paid in advance, if any, stating whether or not Landlord is in
default in performance of any covenant, agreement, term, provision or condition
contained in this Lease and, if so, specifying each such default and such other
facts as Landlord may reasonably request, it being intended that any such
statement delivered pursuant hereto may be relied upon by any prospective
purchaser of the Building or of the Building and the land or of any interest of
Landlord therein, any mortgagee or prospective mortgagee thereof, any lessor or
prospective lessor thereof, any lessee or prospective lessee thereof, or any
prospective assignee of any mortgage thereof. Time is of the essence in respect
of any such requested certificate, Tenant hereby acknowledging the importance of
such certificates in mortgage financing arrangements, prospective sale and the
like.

      17.6  PROHIBITED MATERIALS AND PROPERTY.

      (a) Tenant shall not bring or permit to be brought or kept in or on the
premises or elsewhere in the Building (i) any inflammable, combustible or
explosive fluid, material, chemical or substance including, without limitation,
any Hazardous Materials, as defined in Article 29.11,except for Permitted
Hazardous Materials, as hereinafter defined, which are handled, stored, used,
and transported safely and in accordance with applicable Environmental Laws, as
defined in Article 29.11, (ii) any materials, appliances or equipment
(including, without limitation, materials, appliances and equipment selected by
Tenant for the construction or other preparation of the premises and furniture
and carpeting) which pose any danger to life, safety or health or may cause
damage, injury or death, except for Permitted Hazardous Materials, as
hereinafter defined, which are handled, stored, used, and transported safely and
in accordance with applicable Environmental Laws, as defined in Article 29.11;
(iii) any unique, unusually valuable, rare or exotic property, work of art or
the like unless the same is fully insured under all-risk coverage, or (iv) any
data processing, electronic, optical or other equipment or property of a
delicate, fragile or vulnerable nature unless the same are housed, shielded and
protected against harm and damage, whether by cleaning or maintenance personnel,
radiations or emanations from other equipment now or hereafter installed in the
Building, or otherwise. Nor shall Tenant cause or permit any potentially harmful
air emissions, odors of cooking or other processes, or any unusual or other
objectionable odors or emissions to emanate from or permeate the premises.

                                      -19-
<PAGE>

      (b) "Permitted Hazardous Materials" shall be defined as: (i) standard
office supplies stored in proper containers, (ii) those Hazardous Materials
listed on Exhibit 5, and (iii) such other Hazardous Materials which Tenant uses
in connection with its business in the Premises, provided that Tenant gives
Landlord at least thirty (30) days prior written notice of the introduction of
any such Hazardous Materials to the Premises by delivering for a Hazardous
Material Questionnaire ("HMQ") in the form attached hereto as Exhibit 6, and
provided that Tenant obtains Landlord's prior written approval of any such
Hazardous Material, which approval shall not to be unreasonably withheld. Tenant
shall only have the right to use an approved Hazardous Material subject to, and
in accordance with, the terms of the HMQ provided by Tenant for such Hazardous
Material. Tenant's disclosure obligations under this Article 17.6 shall include
a requirement that, to the extent any information contained in an HMQ previously
delivered by Tenant shall become inaccurate in any material respect, Tenant
shall immediately deliver to Landlord a new updated HMQ. Landlord shall review
and approve or disapprove Tenant's use of the Hazardous Materials disclosed in
Tenant's completed Hazardous Materials Questionnaire within a reasonable time
period following Landlord's receipt thereof.

      17.7  REQUIREMENTS OF LAW--FINES AND PENALTIES.

      (a) Tenant at its sole expense shall comply with all laws, rules, orders
and regulations, including, without limitation, all energy-related requirements,
of Federal, State, County and Municipal Authorities and with any direction of
any public officer or officers, pursuant to law, which shall impose any duty
upon Landlord or Tenant with respect to or arising out of Tenant's use or
occupancy of the premises. Tenant shall reimburse and compensate Landlord for
all expenditures made by, or damages or fines sustained or incurred by, Landlord
due to nonperformance or noncompliance with or breach or failure to observe any
item, covenant, or condition of this Lease upon Tenant's part to be kept,
observed, performed or complied with. If Tenant receives notice of any violation
of law, ordinance, order or regulation applicable to the premises, it shall give
prompt notice thereof to Landlord.

      (b) Landlord shall comply with the Americans with Disabilities Act ("ADA")
so far as the same relates to the common areas of the Building and the Complex,
and the costs so incurred by Landlord may be included in Operating Costs in
accordance with the provisions of Article 9; provided however: (i) that costs of
complying with the ADA shall not be included in Operating Costs to the extent
that such costs are required because the common areas of the Building and the
Complex do not comply with the ADA as of the Execution Date of the Lease, and
(ii) Tenant (and not Landlord) shall be responsible for any work or alterations
to the common areas required by the ADA to the extent that the same are required
because of alterations or work performed by Tenant. Landlord hereby represents
to Tenant that, as of the Execution Date of this Lease, Landlord has not
received any written notice that the common areas of the Building or the Complex
are in violation of the ADA.

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

      17.9 MISCELLANEOUS. Subject to Article 12, Tenant shall not suffer or
permit the premises or any fixtures, equipment or utilities therein or serving
the same, to be overloaded, damaged or defaced, nor permit any hole to be
drilled or made in any part thereof. Tenant shall not suffer or permit any
employee, contractor, business invitee or visitor to violate any covenant,
agreement or obligations of the Tenant under this Lease.

18.   DAMAGE BY FIRE, ETC.

      (a) During the entire term of this Lease, and adjusting insurance
coverages to reflect current values from time to time:--(i) Landlord shall keep
the Building and any other property installed by or at the expense of Tenant)
insured against loss or damage caused by any peril covered under fire, extended
coverage and all risk insurance in an amount equal to one hundred percent (100%)
replacement cost value above foundation walls; and (ii) Tenant shall keep its
personal property in and about the premises insured against loss or damage
caused by any peril covered under fire, extended coverage and all risk
insurance.

                                      -20-
<PAGE>

      (b) If any portion of the premises required to be insured by Landlord
under the preceding paragraph shall be damaged by fire or other insured
casualty, Landlord shall proceed with diligence, subject to the then applicable
statutes, building codes, zoning ordinances, and regulations of any governmental
authority, and at the expense of Landlord (but only to the extent of insurance
proceeds made available to Landlord by any mortgagee and/or ground lessor of the
real property of which the premises are a part) to repair or cause to be
repaired such damage, that such repairs to such Tenant's alterations,
decorations, additions and improvements shall be performed by Landlord but at
Tenant's expense; in all other respects, all repairs to and replacements of
Tenant's property shall be made by and at the expense of Tenant.

      (c) If the premises or any part thereof shall have been rendered unfit for
use and occupation hereunder by reason of such damage the Yearly Rent or a just
and proportionate part thereof, according to the nature and extent to which the
premises shall have been so rendered unfit, shall be suspended or abated until
the premises (except as to the property which is to be repaired by or at the
expense of Tenant) shall have been restored as nearly as practicably may be to
the condition in which they were immediately prior to such fire or other
casualty.

      (d) Tenant agrees to cooperate with Landlord in such manner as Landlord
may reasonably request in assisting Landlord in collecting insurance proceeds
due in connection with any casualty which affects the premises.

      (e) Landlord shall not be liable for delays in the making of any such
repairs which are due to government regulation, casualties and strikes,
unavailability of labor and materials, and other causes beyond the reasonable
control of Landlord, nor shall Landlord be liable for any inconvenience or
annoyance to Tenant or injury to the business of Tenant resulting from delays in
repairing such damage.

      (f) If (i) the premises are so damaged by fire or other casualty (whether
or not insured) at any time during the last eighteen (18) months of the term
hereof that the cost to repair such damage is reasonably estimated to exceed
one-half (1/2) of the total Yearly Rent payable hereunder for the period from
the estimated date of restoration until the Termination Date, or (ii) the
Building (whether or not including any portion of the premises) is so damaged by
fire or other casualty (whether or not insured) that substantial alteration or
reconstruction or demolition of the Building shall in Landlord's judgment be
required, then and in either of such events, this Lease and the term hereof may
be terminated at the election of Landlord by a notice in writing of its election
so to terminate which shall be given by Landlord to Tenant within sixty (60)
days following such fire or other casualty, the effective termination date of
which shall be not less than thirty (30) days after the day on which such
termination notice is received by Tenant.

      (g) In the event of any termination, this Lease and the term hereof shall
expire as of such effective termination date as though that were the Termination
Date as stated in Exhibit 1 and the Yearly Rent shall be apportioned as of such
date; and if the premises or any part thereof shall have been rendered unfit for
use and occupation by reason of such damage the Yearly Rent for the period from
the date of the fire or other casualty to the effective termination date, or a
just and proportionate part thereof, according to the nature and extent to which
the premises shall have been so rendered unfit, shall be abated.

19.   WAIVER OF SUBROGATION

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

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

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

                                      -21-
<PAGE>

from the other or its agents or employees for any loss or damage to its property
or the property of others resulting from fire or other perils covered by such
property insurance.

20.   CONDEMNATION - EMINENT DOMAIN

      In the event that the premises or any material part of the premises, or
the whole or any material part of the Building (the parties hereby agreeing
that, for the purposes of this sentence, "materiality" shall be defined as such
part as shall, in Landlord's bona fide business judgment, render the continued
operation of the Building uneconomic after such taking) shall be taken or
appropriated by eminent domain or shall be condemned for any public or
quasi-public use, or (by virtue of any such taking, appropriation or
condemnation) shall suffer any damage (direct, indirect or consequential) for
which Landlord or Tenant shall be entitled to compensation, then (and in any
such event) this Lease and the term hereof may be terminated at the election of
Landlord by a notice in writing of its election so to terminate which shall be
given by Landlord to Tenant within sixty (60) days following the date on which
Landlord shall have received notice of such taking, appropriation or
condemnation. In the event that a substantial part of the premises or of the
means of access thereto shall be so taken, appropriated or condemned, then (and
in any such event) this Lease and the term hereof may be terminated at the
election of Tenant by a notice in writing of its election so to terminate which
shall be given by Tenant to Landlord within sixty (60) days following the date
on which Tenant shall have received notice of such taking, appropriation or
condemnation.

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

21.   DEFAULT

      21.1 CONDITIONS OF LIMITATION - RE-ENTRY - TERMINATION. This Lease and the
herein term and estate are, upon the condition that if (a) subject to Article
21.7, Tenant shall neglect or fail to perform or observe any of the Tenant's
covenants or agreements herein, including (without limitation) the covenants or
agreements with regard to the payment when due of rent, additional charges,
reimbursement for increase in Landlord's costs, or any other charge payable by
Tenant to Landlord (all of which shall be considered as part of Yearly Rent for
the purposes of invoking Landlord's statutory or other rights and remedies in
respect of payment defaults); or (b) intentionally omitted; or (c) Tenant shall
be involved in financial difficulties as evidenced by an admission in writing by
Tenant of Tenant's inability to pay its debts generally as they become due, or
by the making or offering to make a composition of its debts with its creditors;
or (d) Tenant shall make an assignment or trust mortgage, or other conveyance or
transfer of like nature, of all or a substantial part of its property for the
benefit of its creditors, or (e) an attachment on mesne process, on execution or
otherwise, or other legal process shall issue against Tenant or its property and
a sale of any of its assets shall be held thereunder; or (f) any judgment, final
beyond appeal or any lien, attachment or the like shall be entered, recorded or
filed against Tenant in any court, registry, etc. and Tenant shall fail to pay
such judgment within thirty (30) days after the judgment shall have become final
beyond appeal or to discharge or secure by surety bond such lien, attachment,
etc. within thirty (30) days of such entry, recording or filing, as the case may
be; or (g) the leasehold hereby created shall be taken on execution or by other
process of law and shall not be revested in Tenant within thirty (30) days
thereafter; or (h) a receiver, sequesterer, trustee or similar officer shall be
appointed by a court of competent jurisdiction to

                                      -22-
<PAGE>

take charge of all or any part of Tenant's property and such appointment shall
not be vacated sixty (60) days; or (i) any proceeding shall be instituted by or
against Tenant pursuant to any of the provisions of any Act of Congress or State
law relating to bankruptcy, reorganizations, arrangements, compositions or other
relief from creditors, and, in the case of any proceeding instituted against it,
if Tenant shall fail to have such proceedings dismissed within sixty (60) days
or if Tenant is adjudged bankrupt or insolvent as a result of any such
proceeding, or (j) any event shall occur or any contingency shall arise whereby
this Lease, or the term and estate thereby created, would (by operation of law
or otherwise) devolve upon or pass to any person, firm or corporation other than
Tenant, except as expressly permitted under Article 16 hereof - then, and in any
such event (except as hereinafter in Article 21.2 otherwise provided) Landlord
may, by notice to Tenant, elect to terminate this Lease; and thereupon (and
without prejudice to any remedies which might otherwise be available for arrears
of rent or other charges due hereunder or preceding breach of covenant or
agreement and without prejudice to Tenant's liability for damages as hereinafter
stated), upon the giving of such notice, this Lease shall terminate as of the
date specified therein as though that were the Termination Date as stated in
Exhibit 1. Without being taken or deemed to be guilty of any manner of trespass
or conversion, and without being liable to indictment, prosecution or damages
therefor, Landlord may, forcibly if necessary, enter into and upon the premises
(or any part thereof in the name of the whole); repossess the same as of its
former estate; and expel Tenant and those claiming under Tenant. The words
"re-entry" and "re-enter" as used in this Lease are not restricted to their
technical legal meanings.

      21.2 INTENTIONALLY OMITTED.

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

      either:

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

      or:

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

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

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

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

                                      -23-
<PAGE>

      21.4  FEES AND EXPENSES.

            (a) If Tenant shall default in the performance of any covenant on
Tenant's part to be performed as in this Lease contained, Landlord may, after
thirty (30) days notice to Tenant and Tenant's failure to cure such default
within such time or such longer time as may reasonably be required (except that
no notice shall be required in an emergency), or at any time thereafter, without
notice, perform the same for the account of Tenant. If Landlord, after such
failure to cure, 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 reasonable sum or sums so paid by Landlord
with all costs and damages, plus interest computed as provided in Article 6
hereof.

            (b) Tenant shall pay Landlord's cost and expense, including
reasonable attorneys' fees, incurred (i) in enforcing any obligation of Tenant
under this Lease or (ii) as a result of Landlord, without its fault, being made
party to any litigation pending by or against Tenant or any persons claiming
through or under Tenant. Tenant shall not be obligated to make any payment to
Landlord of any attorneys' fees incurred by Landlord unless judgment is entered
(final, and beyond appeal) in favor of Landlord in the lawsuit relating to such
fees. Landlord shall pay, upon demand by Tenant, reasonable attorneys' fees
incurred by Tenant in connection with any lawsuit between Landlord and Tenant
where judgment is entered (final, and beyond appeal) in favor of Tenant.

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

      21.6 LANDLORD'S REMEDIES NOT EXCLUSIVE. Except as otherwise set forth in
the Lease (including, without limitation, Article 26 hereof), the specified
remedies to which either party may resort hereunder are cumulative and are not
intended to be exclusive of any remedies or means of redress to which such party
may at any time be lawfully entitled, and, except as otherwise set forth in the
Lease (including, without limitation, Article 26 hereof), either party may
invoke any remedy (including the remedy of specific performance) allowed at law
or in equity as if specific remedies were not herein provided for.

      21.7 GRACE PERIOD. Notwithstanding anything to the contrary in this
Article contained, Landlord agrees not to take any action to terminate this
Lease (a) for default by Tenant in the payment when due of any sum of money, if
Tenant shall cure such default within five (5) days after written notice thereof
is given by Landlord to Tenant, provided, however, that no such notice need be
given and no such default in the payment of money shall be curable if on two (2)
prior occasions there had been a default in the payment of money which had been
cured after notice thereof had been given by Landlord to Tenant as herein
provided or (b) for default by Tenant in the performance of any covenant other
than a covenant to pay a sum of money, if Tenant shall cure such default within
a period of thirty (30) days after written notice thereof given by Landlord to
Tenant (except where the nature of the default is such that remedial action
should appropriately take place sooner, as indicated in such written notice), or
within such additional period as may reasonably be required to cure such default
if (because of governmental restrictions or any other cause beyond the
reasonable control of Tenant) the default is of such a nature that it cannot be
cured within such thirty-(30)-day period, provided, however, (1) that there
shall be no extension of time beyond such thirty-(30)-day period for the curing
of any such default unless, not more than ten (10) days after the receipt of the
notice of default, Tenant in writing (i) shall specify the cause on account of
which the default cannot be cured during such period and shall advise Landlord
of its intention duly to institute all steps necessary to cure the default and
(ii) shall, as soon as reasonably practicable, duly institute and thereafter
diligently prosecute to completion all steps necessary to cure such default and,
(2) that no notice of the opportunity to cure a default need be given, and no
grace period whatsoever shall be allowed to Tenant (except to the extent that a
grace period is specifically therein provided), in the event that the default is
based upon a condition set forth in clauses (c), (d), (e), (f), (g), (h), (i) or
(j) of Article 21.1 of this Lease.

22.   END OF TERM - ABANDONED PROPERTY

      Upon the expiration or other termination of the term of this Lease, Tenant
shall peaceably quit and surrender to Landlord the premises and all alterations
and additions thereto, broom clean, in good order, repair and condition (except
as provided herein and in Articles 8.7, 18 and 20) excepting only ordinary wear
and use and damage by fire or other casualty for which, under other provisions
of this Lease, Tenant has no responsibility of repair or restoration. Tenant
shall remove all of its property, including, without limitation, all
telecommunication, computer and other cabling installed by Tenant in the
premises or elsewhere in the Building, and, to the extent specified by Landlord,
all alterations and additions made by Tenant and all partitions wholly within
the premises, and shall repair any damages to the premises or the Building
caused by their installation or by such removal. Tenant's obligation to observe
or perform this covenant shall survive the expiration or other termination of
the term of this Lease.

                                      -24-
<PAGE>

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

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

23.   SUBORDINATION

      (a) Subject to any mortgagee's or ground lessor's election, as hereinafter
provided for, this Lease is subject and subordinate in all respects to all
matters of record (including, without limitation, deeds and land disposition
agreements), ground leases and/or underlying leases, and all mortgages, any of
which may now or hereafter be placed on or affect such leases and/or the real
property of which the premises are a part, or any part of such real property,
and/or Landlord's interest or estate therein, and to each advance made and/or
hereafter to be made under any such mortgages, and to all renewals,
modifications, consolidations, replacements and extensions thereof and all
substitutions therefor. This Article 23 shall be self-operative and no further
instrument or subordination shall be required. In confirmation of such
subordination, Tenant shall execute, acknowledge and deliver promptly any
certificate or instrument that Landlord and/or any mortgagee and/or lessor under
any ground or underlying lease and/or their respective successors in interest
may request, subject to Landlord's, mortgagee's and ground lessor's right to do
so for, on behalf and in the name of Tenant as set forth in Article 23(e).
Notwithstanding anything to the contrary in this Article 23 contained, as to any
future mortgages, ground leases, and/or underlying lease or deeds of trust, the
herein provided subordination and attornment shall be effective only if the
mortgagee, ground lessor or trustee therein, as the case may be, agrees, by a
written instrument in recordable form and in the customary form of such
mortgagee, ground lessor, or trustee ("Nondisturbance Agreement") that, as long
as Tenant shall not be in terminable default of the obligations on its part to
be kept and performed under the terms of this Lease, this Lease will not be
affected and Tenant's possession hereunder will not be disturbed by any default
in, termination, and/or foreclosure of, such mortgage, ground lease, and/or
underlying lease or deed of trust, as the case may be.

      (b) Any such mortgagee or ground lessor may from time to time subordinate
or revoke any such subordination of the mortgage or ground lease held by it to
this Lease. Such subordination or revocation, as the case may be, shall be
effected by written notice to Tenant and by recording an instrument of
subordination or of such revocation, as the case may be, with the appropriate
registry of deeds or land records and to be effective without any further act or
deed on the part of Tenant. In confirmation of such subordination or of such
revocation, as the case may be, Tenant shall execute, acknowledge and promptly
deliver any certificate or instrument that Landlord, any mortgagee or ground
lessor may request, subject to Landlord's, mortgagee's and ground lessor's right
to do so for, on behalf and in the name of Tenant under certain circumstances,
as hereinafter provided in accordance with Article 23(e).

      (c) Without limitation of any of the provisions of this Lease, if any
ground lessor or mortgagee shall succeed to the interest of Landlord by reason
of the exercise of its rights under such ground lease or mortgage (or the
acceptance of voluntary conveyance in lieu thereof) or any third party
(including, without limitation, any foreclosure purchaser or mortgage receiver)
shall succeed to such interest by reason of any such exercise or the expiration
or sooner termination of such ground lease, however caused, then such successor
may, upon notice and request to Tenant (which, in the case of a ground lease,
shall be within thirty (30) days after such expiration or sooner termination),
succeed to the interest of Landlord under this Lease, provided, however, that
such successor shall not: (i) be liable for any previous act or omission of
Landlord under this Lease; (ii) be subject to any offset, defense, or
counterclaim which shall theretofore have accrued to Tenant against Landlord;
(iii) have any obligation with respect to any security

                                      -25-
<PAGE>

deposit unless it shall have been paid over or physically delivered to such
successor; or (iv) be bound by any previous modification of this Lease or by any
previous payment of Yearly Rent for a period greater than one (1) month, made
without such ground lessor's or mortgagee's consent where such consent is
required by applicable ground lease or mortgage documents; provided, however,
the foregoing shall not relieve any such successor from its obligations to
perform maintenance and repairs of continuing nature, the need for which first
arise prior to the time that such successor succeeds to Landlord's interest
under this Lease and which continue after such successor succeeds to Landlord's
interest under this Lease. In the event of such succession to the interest of
the Landlord -- and notwithstanding that any such mortgage or ground lease may
antedate this Lease -- the Tenant shall attorn to such successor and shall ipso
facto be and become bound directly to such successor in interest to Landlord to
perform and observe all the Tenant's obligations under this Lease without the
necessity of the execution of any further instrument. Nevertheless, Tenant
agrees at any time and from time to time during the term hereof to execute a
suitable instrument in confirmation of Tenant's agreement to attorn, as
aforesaid, subject to Landlord's, mortgagee's and ground lessor's right to do so
for, on behalf and in the name of Tenant under certain circumstances, as
provided in Article 23(e).

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

      (e) Tenant hereby irrevocably constitutes and appoints Landlord or any
such mortgagee or ground lessor, and their respective successors in interest,
acting singly, Tenant's attorney-in-fact to execute and deliver any such
certificate or instrument for, on behalf and in the name of Tenant, but only if
Tenant fails to execute, acknowledge and deliver any such certificate or
instrument in the following circumstances:

            1.    Landlord, such mortgagee, or ground lessor ("Requesting
                  Party") shall have given Tenant a written request ("First
                  Request") therefore, stating that if Tenant does not timely
                  execute and deliver such certificate or instrument, the
                  Requesting Party may act as Tenant's attorney-in-fact in
                  accordance with this Article 23(e), together with a
                  Nondisturbance Agreement, as defined in Article 23(a),
                  executed on behalf of the mortgagee, ground lessor, or trustee
                  in question;

            2.    Tenant shall fail to execute and deliver such certificate or
                  instrument within ten (10) days of the First Request;

            3.    The Requesting Party shall, after the expiration of such ten
                  (10) day period, have given Tenant another request ("Second
                  Request") therefor, stating that Tenant has failed timely to
                  respond to the First Request for such certificate or
                  instrument and that if Tenant does not execute and deliver
                  such certificate or instrument within ten (10) days of the
                  Second Request, the Requesting Party may act as Tenant's
                  attorney-in-fact in accordance with this Article 23(e); and

            4.    Tenant shall fail to execute and deliver such certificate or
                  instrument within ten (10) days of the Second Request.

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

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

      (h) Landlord represents to Tenant that, as of the Execution Date of this
Lease, there are no ground leases affecting the Building.

                                      -26-
<PAGE>

24.   QUIET ENJOYMENT

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

25.   ENTIRE AGREEMENT - WAIVER - SURRENDER

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

      25.2 WAIVER 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 in the Building shall not be deemed a waiver of any such Rules
and Regulations. Notwithstanding the foregoing, Landlord agrees that it will not
enforce said Rules and Regulations against Tenant in a discriminatory or
arbitrary manner, as compared to similarly situated tenants. 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 an accord and satisfaction, and Landlord may accept such check or
payment without prejudice to Landlord's right to recover the balance of such
rent or pursue any other remedy in this Lease provided.

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

26.   INABILITY TO PERFORM - EXCULPATORY CLAUSE

      (a) Except as provided in Article 4.1, 4.2, 8.8 and 15.6 hereof, this
Lease and the obligations of Tenant to pay rent hereunder and perform all the
other covenants, agreements, terms, provisions and conditions hereunder on the
part of Tenant to be performed shall in no way be affected, impaired or excused
because Landlord is unable to fulfill any of its obligations under this Lease or
is unable to supply or is delayed in supplying any service expressly or
impliedly to be supplied or is unable to make or is delayed in making any
repairs, replacements, additions, alterations, improvements or decorations or is
unable to supply or is delayed in supplying any equipment or fixtures if
Landlord is prevented or delayed from so doing by reason of strikes or labor
troubles or any other similar or dissimilar cause whatsoever beyond Landlord's
reasonable control, including but not limited to, governmental preemption in
connection with a national emergency or by reason of any rule, order or
regulation of any department or subdivision thereof of any governmental agency
or by reason of the conditions of supply and demand which have been or are
affected by war, hostilities or other similar or dissimilar emergency ("Force
Majeure"). In each such instance of inability of Landlord to perform, Landlord
shall exercise reasonable diligence to eliminate the cause of such inability to
perform.

      (b) Tenant shall neither assert nor seek to enforce any claim against
Landlord, or Landlord's agents or employees, or the assets of Landlord or of
Landlord's agents or employees, for breach of this Lease or otherwise, other
than against Landlord's interest in the Building of which the premises are a
part and in the uncollected rents, issues and profits thereof, and Tenant agrees
to look solely to such interest for the satisfaction of any liability of
Landlord under this Lease, it being specifically agreed that in no event shall
Landlord or Landlord's agents or employees (or any of the officers, trustees,
directors, partners, beneficiaries, joint venturers,

                                      -27-
<PAGE>

members, stockholders or other principals or representatives, and the like,
disclosed or undisclosed, thereof) ever be personally liable for any such
liability. This paragraph shall not limit any right that Tenant might otherwise
have to obtain injunctive relief against Landlord or to take any other action
which shall not involve the personal liability of Landlord to respond in
monetary damages from Landlord's assets other than the Landlord's interest in
said real estate, as aforesaid. In no event shall Landlord or Landlord's agents
or employees (or any of the officers, trustees, directors, partners,
beneficiaries, joint venturers, members, stockholders or other principals or
representatives and the like, disclosed or undisclosed, thereof) ever be liable
for consequential or incidental damages. Without limiting the foregoing, in no
event shall Landlord or Landlord's agents or employees (or any of the officers,
trustees, directors, partners, beneficiaries, joint venturers, members,
stockholders or other principals or representatives and the like, disclosed or
undisclosed, thereof) ever be liable for lost profits of Tenant. If by reason of
Landlord's failure to acquire title to the real property of which the premises
are a part or to complete construction of the Building or premises, Landlord
shall be held to be in breach of this Lease, Tenant's sole and exclusive remedy
shall be a right to terminate this Lease.

      (c) Landlord shall not be deemed to be in default of its obligations under
the Lease unless Tenant has given Landlord written notice of such default, and
Landlord has failed to cure such default within thirty (30) days after Landlord
receives such notice or such longer period of time as Landlord may reasonably
require to cure such default. Except as otherwise expressly provided in this
Lease, in no event shall Tenant have the right to terminate the Lease nor shall
Tenant's obligation to pay Yearly Rent or other charges under this Lease abate
based upon any default by Landlord of its obligations under the Lease. Nothing
in this Article 26 shall extend or delay Tenant's abatement or termination
rights under Articles 8.8 or 15.6.

27.   BILLS AND NOTICES

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

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

      All bills and statements for reimbursement or other payments or charges
due from Tenant to Landlord hereunder shall be due and payable in full ten (10)
days, unless herein otherwise provided, after submission thereof by Landlord to
Tenant. Tenant's failure to make timely payment of any amounts indicated by such
bills and statements, whether for work done by Landlord at Tenant's request,
reimbursement provided for by this Lease or for any other sums properly owing by
Tenant to Landlord, shall be treated as a default in the payment of rent, in
which event Landlord shall have all rights and remedies provided in this Lease
for the nonpayment of rent.

28.   PARTIES BOUND - SEIZIN OF TITLE

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

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

                                      -28-
<PAGE>

29.   MISCELLANEOUS

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

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

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

      29.4  MODIFICATIONS. Intentionally omitted.

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

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

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

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

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

                                      -29-
<PAGE>

      29.8 REPRESENTATION OF AUTHORITY. By his execution hereof each of the
signatories on behalf of the respective parties hereby warrants and represents
to the other that he is duly authorized to execute this Lease on behalf of such
party.

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

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

      29.11 HAZARDOUS MATERIALS. Landlord and Tenant agree as follows with
respect to the existence or use of "Hazardous Material" in or on the Premises.

      (a) Tenant, at its sole cost and expense, shall comply with all laws,
statutes, ordinances, rules and regulations of any local, state or federal
governmental authority having jurisdiction concerning environmental, health and
safety matters (collectively, "Environmental Laws"), including, but not limited
to, any discharge into the air, surface, water, sewers, soil or groundwater of
any Hazardous Material (as defined in Article 29.11(c)), whether within or
outside the premises within the Complex. Notwithstanding the foregoing, nothing
contained in this Lease requires, or shall be construed to require, Tenant to
incur any liability related to or arising from environmental conditions (i) for
which the Landlord is responsible pursuant to the terms of this Lease, or (ii)
which existed within the premises or the Complex prior to the date Tenant takes
possession of the premises.

      (b) Subject to Article 17.6, Tenant shall not cause or permit any
Hazardous Material to be brought upon, kept or used in or about the premises or
otherwise in the Complex by Tenant, its agents, employees, contractors or
invitees, without the prior written consent of Landlord, except for Hazardous
Materials which are typically used in the operation of offices or laboratories,
provided that such materials are stored, used and disposed of in strict
compliance with all applicable Environmental Laws and with good scientific and
medical practice. Notwithstanding the foregoing, with respect to any of Tenant's
Hazardous Material which Tenant does not properly handle, store or dispose of in
compliance with all applicable Environmental Laws and good scientific and
medical practice, Tenant shall, upon written notice from Landlord, no longer
have the right to bring such material into the buildings or the Complex until
Tenant has demonstrated, to Landlord's reasonable satisfaction, that Tenant has
implemented programs to thereafter properly handle, store or dispose of such
material.

      (c) As used herein, the term "Hazardous Material" means any hazardous or
toxic substance, material or waste or petroleum derivative which is or becomes
regulated by any Environmental Law, specifically including live organisms,
viruses and fungi, medical waste, and so-called "biohazard" materials. The term
"Hazardous Material" includes, without limitation, any material or substance
which is (i) designated as a "hazardous substance" pursuant to Section 1311 of
the Federal Water Pollution Control Act (33 U.S.C. Section 1317), (ii) defined
as a "hazardous waste" pursuant to Section 1004 of the Federal Resource
Conservation and Recovery Act, 42 U.S.C. Section 6901 et seq. (42 U.S.C. Section
6903), (iii) defined as a "hazardous substance" pursuant to Section 101 of the
Comprehensive Environmental Response, Compensation and Liability Act, 42 U.S.C.
Section 9601 et seq. (42 U.S.C. Section 9601), (iv) defined as "hazardous
substance" or "oil" under Chapter 21E of the General Laws of Massachusetts, or
(v) a so-called "biohazard" or medical waste, or is contaminated with blood or
other bodily fluids; and "Environmental Laws" include, without limitation, the
laws listed in the preceding clauses (i) through (iv).

      (d) Any increase in the premium for necessary insurance on the Premises or
the Complex which arises from Tenant's use and/or storage of these Hazardous
Materials shall be solely at Tenant's expense. Tenant shall procure and maintain
at its sole expense such additional insurance as may be necessary to comply with
any requirement of any Federal, State or local government agency with
jurisdiction.

      (e) Tenant hereby covenants and agrees to indemnify, defend and hold
Landlord harmless from any and all claims, judgments, damages, penalties, fines,
costs, liabilities or losses (collectively "Losses") which Landlord may
reasonably incur arising out of contamination of real estate, the Complex or
other property not a part of the premises, which contamination arises as a
result of: (i) the presence of Hazardous Material in the premises, the presence
of which is caused or permitted by Tenant, or (ii) from a breach by Tenant of
its obligations under this Article 29.11. This indemnification of Landlord by
Tenant includes, without limitation, reasonable

                                      -30-
<PAGE>

costs incurred in connection with any investigation of site conditions or any
cleanup, remedial, removal or restoration work required by any federal, state or
local governmental agency or political subdivision because of Hazardous Material
present in the soil or ground water on or under the premises based upon the
circumstances identified in the first sentence of this Article 29.11(e). The
indemnification and hold harmless obligations of Tenant under this Article
29.11(e) shall survive any termination of this Lease. Without limiting the
foregoing, if the presence of any Hazardous Material in the buildings or
otherwise in the Complex caused or permitted by Tenant results in any
contamination of the premises, Tenant shall promptly take all actions at its
sole expense as are necessary to return the premises to a condition which
complies with all Environmental Laws; provided that Landlord's approval of such
actions shall first be obtained, which approval shall not be unreasonably
withheld so long as such actions, in Landlord's reasonable discretion, would not
potentially have any materially adverse long-term or short-term effect on the
premises, and, in any event, Landlord shall not withhold its approval of any
proposed actions which are required by applicable Environmental Laws.

      (f) On or before the date that Tenant, and anyone claiming by, through or
under Tenant, vacates the Premises, and immediately prior to the time that
Tenant delivers the premises to Landlord, Tenant shall provide to Landlord a
copy of its most current chemical waste removal manifest and a certification
from Tenant executed by an officer of Tenant that no Hazardous Materials or
other potentially dangerous or harmful chemicals brought onto the premises from
and after the date that Tenant first took occupancy of the premises remain in
the premises.

      29.12 PATRIOT ACT.

      (a)   Tenant represents and warrants to Landlord that:

            (1)   Tenant is not in violation of any Anti-Terrorism Law;

            (2)   Tenant is not, as of the date hereof:

                  (i)   conducting any business or engaging in any transaction
                        or dealing with any Prohibited Person, including the
                        making or receiving of any contribution of funds, goods
                        or services to or for the benefit of any Prohibited
                        Person;

                  (ii)  dealing in, or otherwise engaging in any transaction
                        relating to, any property or interests in property
                        blocked pursuant to Executive Order No. 13224; or

                  (iii) engaging in or conspiring to engage in any transaction
                        that evades or avoids, or has the purpose of evading or
                        avoiding, or attempts to violate any of the prohibitions
                        set forth in, any Anti-Terrorism Law; and

            (3)   Neither Tenant nor any of its affiliates, officers, directors,
                  shareholders, members or lease guarantor, as applicable, is a
                  Prohibited Person.

      (b) If at any time any of these representations becomes false, then it
shall be considered a material default under this Lease.

      (c) As used herein, "Anti-Terrorism Law" is defined as any law relating to
terrorism, anti-terrorism, money-laundering or anti-money laundering activities,
including without limitation the United States Bank Secrecy Act, the United
States Money Laundering Control Act of 1986, Executive Order No. 13224, and
Title 3 of the USA Patriot Act, and any regulations promulgated under any of
them. As used herein "Executive Order No. 13224" is defined as Executive Order
No. 13224 on Terrorist Financing effective September 24, 2001, and relating to
"Blocking Property and Prohibiting Transactions With Persons Who Commit,
Threaten to Commit, or Support Terrorism", as may be amended from time to time.
"Prohibited Person" is defined as (i) a person or entity that is listed in the
Annex to Executive Order No. 13224, or a person or entity owned or controlled by
an entity that is listed in the Annex to Executive Order No. 13224; (ii) a
person or entity with whom Landlord is prohibited from dealing or otherwise
engaging in any transaction by any Anti-Terrorism Law; or (iii) a person or
entity that is named as a "specially designated national and blocked person" on
the most current list published by the U.S. Treasury Department Office of
Foreign Assets Control at its official website,
http://www.treas.gov/ofac/t11sdn.pdf or at any replacement website or other
official publication of such list. "USA Patriot Act" is defined as the "Uniting
and Strengthening America by Providing Appropriate Tools Required to Intercept
and Obstruct Terrorism Act of 2001" (Public Law 107-56), as may be amended from
time to time.

      (d) Notwithstanding, with respect to any entity which is a publicly traded
company, Tenant shall not be responsible, under this Article 29.12, for any
person who owns, or controls, either directly or indirectly in the aggregate,
less than five (5%) percent of the equity interest in such entity.

                                      -31-
<PAGE>

      29.13 LETTER OF CREDIT.

      (a) Tenant acknowledges that Landlord is unwilling to execute the Lease
unless Tenant provides Landlord with additional security for Tenant's
obligations under the Lease. Therefore, Tenant shall deliver to Landlord, on the
date that Tenant executes and delivers the Lease to Landlord, an Irrevocable
Standby Letter of Credit ("Letter of Credit") which shall be (1) in the form
attached hereto as Exhibit 7, (2) issued by a bank reasonably acceptable to
Landlord with minimum assets of Ten Billion Dollars ($10,000,000,000.00), upon
which presentment may be made in Boston, Massachusetts, (3) in an amount equal
to Four Hundred Ten Thousand Seven Hundred Seventy-One and 25/100 ($410,771.25)
Dollars and (4) for a term of one (1) year, subject to extension in accordance
with the terms of the Letter of Credit. Tenant shall, on or before the date
thirty (30) days prior to the expiration of the term of such Letter of Credit,
deliver to Landlord a new Letter of Credit satisfying the foregoing conditions
("Substitute Letter of Credit") in lieu of the Letter of Credit then being held
by Landlord. Such Letter of Credit shall be automatically renewable in
accordance with the provisions of Exhibit 7; provided that if the issuer of such
Letter of Credit gives notice of its election not to renew such Letter of Credit
for any additional period pursuant thereto, Tenant shall be required to deliver
a Substitute Letter of Credit satisfying the conditions hereof, on or before the
date thirty (30) days prior to the expiration of the term of such Letter of
Credit. Tenant agrees that it shall from time to time, as necessary, whether as
a result of a draw on the Letter of Credit by Landlord pursuant to the terms
hereof or as a result of the expiration of the Letter of Credit then in effect,
renew or replace the original and any subsequent Letter of Credit so that a
Letter of Credit, in the amount required hereunder, is in effect until a date
which is at least 60 days after the Termination Date of the Lease. If Tenant
fails to furnish such renewal or replacement at least 60 days prior to the
stated expiration date of the Letter of Credit then held by Landlord, Landlord
may draw upon such Letter of Credit and hold the proceeds thereof (and such
proceeds need not be segregated) as a Security Deposit pursuant to the terms of
this Article 29.13.

      (b) In the event that Tenant is in default of its obligations under the
Lease, then the Landlord shall have the right, at any time after such event,
without giving any further notice to Tenant, to draw down from said Letter of
Credit (Substitute Letter of Credit or Additional Letter of Credit, as defined
below, as the case may be) (a) the amount necessary to cure such default or (b)
if such default cannot reasonably be cured by the expenditure of money, to
exercise all rights and remedies Landlord may have on account of such default,
the amount which, in Landlord's opinion, is necessary to satisfy Tenant's
Liability in account thereof. In the event of any such draw by the Landlord,
Tenant shall, within fifteen (15) business days of written demand therefor,
deliver to Landlord an additional Letter of Credit satisfying the foregoing
conditions ("Additional Letter of Credit"), except that the amount of such
Additional Letter of Credit shall be the amount of such draw. In addition, in
the event of a termination based upon the default of Tenant under the Lease, or
a rejection of the Lease pursuant to the provisions of the Federal Bankruptcy
Code, Landlord shall have the right to draw upon the Letter of Credit (from time
to time, if necessary) to cover the full amount of damages and other amounts due
from Tenant to Landlord under the Lease. Any amounts so drawn shall, at
Landlord's election, be applied first to any unpaid rent and other charges which
were due prior to the filing of the petition for protection under the Federal
Bankruptcy Code. Tenant hereby covenants and agrees not to oppose, contest or
otherwise interfere with any attempt by Landlord to draw down from said Letter
of Credit including, without limitation, by commencing an action seeking to
enjoin or restrain Landlord from drawing upon said Letter of Credit. Tenant also
hereby expressly waives any right or claim it may have to seek such equitable
relief. In addition to whatever other rights and remedies it may have against
Tenant if Tenant breaches its obligations under this paragraph, Tenant hereby
acknowledges that it shall be liable for any and all damages which Landlord may
suffer as a result of any such breach.

      (c) Upon request of Landlord or any (prospective) purchaser or mortgagee
of the Building, Tenant shall, at its expense, cooperate with Landlord in
obtaining an amendment to or replacement of any Letter of Credit which Landlord
is then holding so that the amended or new Letter of Credit reflects the name of
the new owner of the Building.

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

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

      (f) Notwithstanding anything herein to the contrary, Tenant shall have the
right to reduce the amount of the Letter of Credit to $273,850.20, effective as
of the second (2nd) anniversary of the Rent Commencement Date if Tenant
satisfies all of the following conditions: (i) Tenant is not in default of its
obligations under this Lease as of the second (2nd) anniversary of the Rent
Commencement Date, (ii) Tenant is in full compliance with the terms of the Lease
as of second (2nd) anniversary of the Rent Commencement Date; and (iii) prior to
the second (2nd) anniversary of the Rent Commencement Date, there have been no
default by Tenant in its obligations under the Lease which has not been cured
within any applicable notice and grace period. Such reduction of

                                      -32-
<PAGE>

the Letter of Credit may be effected either by Tenant providing Landlord with a
substitute Letter of Credit in the reduced amount (which Landlord shall exchange
for the Letter of Credit which Landlord is then holding), or by Tenant providing
to Landlord an amendment to the Letter of Credit, in form reasonably acceptable
to Landlord, effecting the reduction, which amendment must be accepted by
Landlord in writing before it is effective.

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

      (a) On the conditions, which conditions Landlord may waive, at its
election, by written notice to Tenant at any time, that Tenant is not in default
of its covenants and obligations under the Lease, and that Idenix
Pharmaceuticals, Inc., itself, an Assignee and/or any Affiliated Entity, each as
defined in Article 16, are occupying the entirety of the premises then demised
to Tenant, both as of the time of option exercise and as of the commencement of
the hereinafter described additional term, Tenant shall have the option to
extend the term of this Lease for one (1) additional four (4) year term, such
additional term commencing as of the expiration of the initial term of the
Lease. Tenant may exercise such option to extend by giving Landlord written
notice on or before the date nine (9) months prior to the expiration date of the
initial term of the Lease. Upon the timely giving of such notice, the term of
this Lease shall be deemed extended upon all of the terms and conditions of this
Lease, except that Landlord shall have no obligation to construct or renovate
the premises and that the Yearly Rent, Operating Costs in the Base Year, and Tax
Base during such additional term shall be as hereinafter set forth. If Tenant
fails to give timely notice, as aforesaid, Tenant shall have no further right to
extend the term of this Lease, time being of the essence of this Article 29.14.

      (b) The Yearly Rent during such additional term shall be based upon
ninety-five percent (95%) of the Fair Market Rental Value, as defined in Article
29.15, as of the commencement of such additional term, of the premises then
demised to Tenant. Landlord shall, on or before the date thirty (30) days after
Landlord's receipt of written request from Tenant made on or after the date
twelve (12) months prior to the expiration of the term of the Lease, give
Landlord's good faith estimate of such Yearly Rent to Tenant.

      (c) The Building Operating Costs Base during such additional term shall be
the actual amount of Building Operating Costs for calendar year 2009.

      (d) The Common Operating Costs Base during such additional term shall bet
the actual amount of Common Operating Costs for calendar year 2009.

      (e) The Building Tax Base during such additional term shall be the actual
amount of Building Taxes payable during fiscal/tax year 2010 (i.e., July 1, 2009
- June 30, 2010).

      (f) The Common Tax Base during such additional term shall be the actual
amount of Common Taxes payable during fiscal/tax year 2010 (i.e., July 1, 2009 -
June 30, 2010).

      (g) Tenant shall have no further option to extend the term of the Lease
other than the one (1) additional four (4) year term herein provided.

      (h) Notwithstanding the fact that upon Tenant's exercise of the herein
option to extend the term of the Lease such extension shall be self-executing,
as aforesaid, the parties shall promptly execute a lease amendment reflecting
such additional term after Tenant exercises the herein option, except that the
Yearly Rent payable in respect of such additional term may not be set forth in
said amendment. Subsequently, after such Yearly Rent is determined, the parties
shall execute a written agreement confirming the same. The execution of such
lease amendment shall not be deemed to waive any of the conditions to Tenant's
exercise of its rights under this Article 29.14, unless otherwise specifically
provided in such lease amendment.

      29.15 DEFINITION OF FAIR MARKET RENTAL VALUE.

      (a) "Fair Market Rental Value" shall be computed as of the date in
question at the then current annual rental charge (i.e., the sum of Yearly Rent
plus escalation and other charges), including provisions for subsequent
increases and other adjustments for leases or agreements to lease then being
executed for comparable space located elsewhere in first-class office buildings
located in East Cambridge, Massachusetts. In determining Fair Market Rental
Value, the following factors, among others, shall be taken into account and
given effect: size, location of premises, lease term, condition of building, and
services provided by the Landlord, but shall not consider the value of
improvements made to the premises by Tenant, which Tenant has the right to
remove at the end of the term of the Lease.

      (b) Dispute as to Fair Market Rental Value

                                      -33-
<PAGE>

      Landlord shall initially designate Fair Market Rental Value and Landlord
shall furnish data in support of such designation on or before the date which
the later of thirty (30) days after Tenant exercises the extension option in
question, or the date which is eight (8) months prior to the commencement of the
extension term in question. If Tenant disagrees with Landlord's designation of a
Fair Market Rental Value, Tenant shall have the right, by written notice given
within thirty (30) days after Tenant has been notified of Landlord's
designation, to submit such Fair Market Rental Value to arbitration. Fair Market
Rental Value shall be submitted to arbitration as follows: Fair Market Rental
Value shall be determined by impartial arbitrators, one to be chosen by the
Landlord, one to be chosen by Tenant, and a third to be selected, if necessary,
as below provided. The unanimous written decision of the two first chosen,
without selection and participation of a third arbitrator, or otherwise, the
written decision of a majority of three arbitrators chosen and selected as
aforesaid, shall be conclusive and binding upon Landlord and Tenant. Landlord
and Tenant shall each notify the other of its chosen arbitrator within ten (10)
days following the call for arbitration and, unless such two arbitrators shall
have reached a unanimous decision within thirty (30) days after their
designation, they shall so notify the President of the Boston Bar Association
(or such organization as may succeed to said Boston Bar Association) and request
him or her to select an impartial third arbitrator, who shall be an office
building owner or a real estate broker dealing with like types of properties, to
determine Fair Market Rental Value as herein defined. Such third arbitrator and
the first two chosen shall, subject to commercial arbitration rules of the
American Arbitration Association, hear the parties and their evidence and render
their decision within thirty (30) days following the conclusion of such hearing
and notify Landlord and Tenant thereof. Landlord and Tenant shall bear the
expense of the third arbitrator (if any) equally. The decision of the arbitrator
shall be binding and conclusive, and judgment upon the award or decision of the
arbitrator may be entered in the appropriate court of law (as identified on
Exhibit 1); and the parties consent to the jurisdiction of such court and
further agree that any process or notice of motion or other application to the
Court or a Judge thereof may be served outside the Commonwealth of Massachusetts
by registered mail or by personal service, provided a reasonable time for
appearance is allowed. If the dispute between the parties as to a Fair Market
Rental Value has not been resolved before the commencement of Tenant's
obligation to pay rent based upon such Fair Market Rental Value, then Tenant
shall pay Yearly Rent and other charges under the Lease in respect of the
premises in question based upon the Fair Market Rental Value designated by
Landlord until either the agreement of the parties as to the Fair Market Rental
Value, or the decision of the arbitrators, as the case may be, at which time
Tenant shall pay any underpayment of rent and other charges to Landlord, or
Landlord shall refund any overpayment of rent and other charges to Tenant.

      29.16 TENANT'S RIGHTS OF FIRST OFFER.

      On the conditions (which conditions Landlord may waive, at its election,
by written notice to Tenant at any time) that Tenant is not in default of its
covenants and obligations under the Lease and that and that Idenix
Pharmaceuticals, Inc., itself, an Assignee and/or any Affiliated Entity, each as
defined in Article 16, are occupying the entirety of the premises then demised
to Tenant, both at the time that Landlord is required to give Landlord's Notice,
as hereinafter defined, and as of the Term Commencement Date in respect of the
RFO Premises, as hereinafter defined, Tenant shall have the following right,
throughout the term of the Lease, to lease the RFO Premises, as hereinafter
defined, when the RFO Premises become available for lease to Tenant, as
hereinafter defined.

      (a) Definition of RFO Premises

      "RFO Premises" shall be defined as: (i) any separately demised portion of
the balance (i.e. other than the portion of initially demised to Tenant) of the
fourth (4th) floor of the Building ("Fourth Floor RFO Premises"), and (ii) any
separately demised portion of the balance of the fifth (5th) floor of the
Building ("Fifth Floor RFO Premises"), in each case when such area becomes
available for lease to Tenant, as hereinafter defined. Tenant acknowledges and
agrees that the Fourth Floor RFO Premises are currently leased to another tenant
pursuant to a lease which will expire as of July 24, 2005, and the Fifth Floor
RFO Premises are leased to another tenant pursuant to a lease which will expire
as of December 24, 2006, subject to such tenant's rights to extend the term of
such lease.

      (b) Definition of Available for Lease to Tenant. A RFO Premises shall be
deemed to be "available for lease to Tenant" when Landlord determines that the
then current tenant of such space will vacate such area and Landlord intends to
market such area to third parties. Tenant acknowledges that Landlord may
simultaneously give a Landlord Notice to Tenant at the same time that Landlord
is offering an RFO Premises to third parties; however, the rights of any such
third party shall be subject to Tenant's rights under this Article 29.16. In no
event shall Tenant have any rights under this Article 29.16 on or after the date
twelve (12) months prior to the expiration of the then current term of the Lease
(i.e. Landlord shall have no obligation to give Landlord's Notice, as
hereinafter defined, to Tenant on or after the date twelve (12) months prior to
the expiration of the then current term of the Lease). In addition, it shall be
a condition to Tenant's exercise of its rights under this Article 29.16 with
respect to any RFO Premises which is offered to be leased to Tenant pursuant to
a Landlord's Notice which is given to Tenant during the period between the date
twenty-four (24) months prior to the expiration of the then current term of the
Lease and the date twelve (12) months prior to the expiration of the then
current term of the Lease, that Tenant shall, at the time that it gives Tenant's
Exercise Notice with respect to such RFO Premises, exercise its option to extend
the term of the Lease as provided in Article 29.14.

      (c) Exercise of Right to Lease RFO Premises

                                      -34-
<PAGE>

      Landlord shall give Tenant written notice ("Landlord's Notice") at the
time that Landlord determines, as aforesaid, that an RFO Premises will become
available for lease to Tenant. Landlord's Notice shall set forth the exact
location of the RFO Premises, the Yearly Rent ("Offered Yearly Rent") which
Landlord is willing to lease such RFO Premises to Tenant, the estimated Term
Commencement Date in respect of such RFO Premises, and such other terms on which
Landlord is willing to lease such RFO Premises to Tenant in accordance with this
Article 29.16. Tenant shall have the right, exercisable upon written notice
("Tenant's Exercise Notice") given to Landlord within ten (10) business days
after the receipt of Landlord's Notice, to lease such RFO Premises. Upon the
timely giving of such notice, Landlord shall lease and demise to Tenant and
Tenant shall hire and take from Landlord, such RFO Premises, upon all of the
same terms and conditions of the Lease except as hereinafter set forth. If
Tenant fails timely to give Tenant's Exercise Notice pursuant to this Article
29.16, then Landlord shall have the right to lease an RFO Premises to a third
party ("Next Tenant") without first offering to lease it to Tenant pursuant to
this Article 29.16, and, except as set forth in Article 29.16(d), Tenant shall
not have the right to lease such RFO Premises pursuant to this Article 29.16
until such RFO Premises becomes available for reletting after the Next Tenant
vacates such RFO Premises.

      (d) Reoffer to Tenant

      Notwithstanding the foregoing, if Tenant does not timely give Tenant's
Exercise Notice to Landlord with respect to a particular RFO Premises, then
Landlord shall be required to give Tenant a new Landlord's Notice with respect
to such RFO Premises prior to entering into a lease of such RFO Premises with a
third party in either of the following circumstances: (i) Landlord does not
enter into a lease of such RFO Premises with a third party on or before the date
one hundred four (104) days after Landlord gives Landlord's Notice with respect
to such RFO Premises, (ii) Landlord elects to lease such RFO Premises as part
(or all) of an area containing more than one hundred twenty (120%) percent of
the Total Rentable Area of such RFO Premises or less than eighty (80%) percent
of the Total Rentable Area of such RFO Premises, or (iii) ninety (90%) percent
of the effective Yearly Rent (i.e. taking into account all economic terms) which
Landlord is willing to enter into a lease of such RFO Premises with a third
party is less than effective Yearly Rent set forth in Landlord's Notice.

      (e) Lease Provisions Applying to RFO Premises

      The leasing to Tenant of such RFO Premises shall be upon all of the same
terms and conditions of the Lease, except as follows:

            (1)   Term Commencement Date

            The Term Commencement Date in respect of such RFO Premises shall be
the later of: (x) the estimated Commencement Date in respect of such RFO
Premises as set forth in Landlord's Notice, or (y) the date that Landlord
delivers such RFO Premises to Tenant.

            (2)   Yearly Rent

            The Yearly Rent rental rate in respect of such RFO Premises shall be
based the Offered Yearly Rent set forth in Landlord's Notice. The Rent
Commencement Date in respect of any RFO Premises shall be the Term Commencement
Date in respect of such RFO Premises.

            (3)   Condition of RFO Premises

            Tenant shall take such RFO Premises "as-is" in its then (i.e. as of
the date of premises delivery) state of construction, finish, and decoration,
without any obligation on the part of Landlord to construct or prepare any RFO
Premises for Tenant's occupancy, and without any obligation on the part of
Landlord to provide any contribution to Tenant towards the preparation of such
RFO Premises for Tenant's occupancy. The Fair Market Rental Value of such RFO
Premises shall be established with due consideration to the provisions of this
Article 29.16(e)(3) as well as other factors.

      (d) Execution of Lease Amendments

            Notwithstanding the fact that Tenant's exercise of the
above-described option to lease RFO Premises shall be self-executing, as
aforesaid, the parties hereby agree promptly to execute a lease amendment
reflecting the addition of an RFO Premises, except that the Yearly Rent payable
in respect of such RFO Premises, Operating Costs in the Base Year in respect of
such RFO Premises, and Tax Base in respect of such RFO Premises may not be as
set forth in such Amendment. At the time that such Yearly Rent, Operating Costs
in the Base Year and Tax Base are determined, the parties shall execute a
written agreement confirming

                                      -35-
<PAGE>

the same. The execution of such lease amendment shall not be deemed to waive any
of the conditions to Tenant's exercise of the herein option to lease the RFO
Premises, unless otherwise specifically provided in such lease amendment.

      29.17 TENANT'S EXPANSION NEEDS.

      Landlord will, upon Tenant's written request, from time to time, meet with
Tenant on a quarterly basis to review Tenant's space needs ("Tenant's Expansion
Needs") and to review those premises in the Building which may then be available
to suit Tenant's needs. If Landlord is not able to satisfy Tenant's Expansion
Needs and/or if Landlord and Tenant are not able to agree to mutually acceptable
terms for such Expansion Space, then such failure shall not be a default by
Landlord and neither party shall have any obligation to the other party pursuant
to this Article 29.17.

      29.18 PARKING. During the term of the Lease, the Landlord will make
available to Tenant fifty-one (51) monthly parking passes for use in the One
Kendall Square Garage ("OKS Garage"). Tenant shall have no right to sublet,
assign, or otherwise transfer said parking passes. Said parking passes shall be
paid for by Tenant at the then current prevailing rate in the Garage, as such
rate may vary from time to time. The current rate for such passes as of the
Execution Date of this Lease is $200.00 per month which may not be increased by
more than five (5%) percent prior to the first (1st) anniversary of the
Occupancy Date. If, for any reason, Tenant shall fail timely to pay the charge
for said parking passes, Tenant shall have no further right to such parking
passes under this Article 29.18. In addition, during any time period when Tenant
is in default beyond the expiration of any applicable notice and grace periods
of its obligations under the Lease, Landlord shall have the right to withdraw
Tenant's use of said parking passes. Said parking passes will be on an
unassigned, non-reserved basis, and shall be subject to reasonable rules and
regulations from time to time in force.

      29.19 ANTENNA AREA. Tenant shall have the right to use the Antenna Area,
as hereinafter defined, to install satellite dish antenna with a diameter not to
exceed twelve (12) inches in diameter ("Antenna") for a period commencing as of
the date that Tenant installs the Antenna, as hereinafter defined, in the
Antenna Area ("Term Commencement Date in respect of the Antenna Area") and
terminating as of the expiration or prior termination of the term of the Lease.
The "Antenna Area" shall be an area on the roof of the Building designated by
Landlord. Tenant shall be permitted to use the Antenna Area solely for one (1)
Antenna installed in accordance with specifications approved by Landlord in
advance (which approval shall not be unreasonably withheld) utilizing a
frequency or frequencies and transmission power identified in such approved
specifications which Tenant will be installing in the Antenna Area and no other
frequencies or transmission power shall be used by Tenant without Landlord's
prior written consent. Such installation shall be designed in such manner as to
be easily removable and so as not to damage the roof of the Building. The
Antenna and any replacement shall be subject to Landlord's approval (which
approval shall not be unreasonably withheld). Tenant's use of the Antenna Area
shall be upon all of the conditions of the Lease, except as follows:

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

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

      C. Tenant shall have no right to make any changes, alterations, signs,
decoration, or other improvements (which changes, alterations, signs, decoration
or other improvements, together with the Antenna, are hereby collectively
referred to as "Rooftop Installations") to the Antenna Area or to the Antenna
without Landlord's prior written consent, which consent Landlord may hold it its
sole discretion.

      D. Tenant shall have no right of access to the roof of the Building unless
Tenant has given Landlord reasonable advance notice and unless Tenant's
representatives are accompanied by a representative of Landlord. Landlord shall
provide Tenant with 24-hour access to the Antenna Area, subject to Landlord's
reasonable security procedures and restrictions based on emergency conditions
and to other causes beyond Landlord's reasonable control. Tenant shall give
Landlord reasonable advance written notice of the need for access to the Antenna
Area (except that such notice may be oral in an emergency), and Landlord must be
present during any entry by Tenant onto the Antenna Area. Each notice for access
shall be in the form of a work order referencing the lease and describing, as
applicable, the date access is needed, the name of the contractor or other
personnel requiring access, the name of the supervisor authorizing the
access/work, the areas to which access is required, the Building common elements
to be impacted (risers, electrical rooms, etc.) and the description of new
equipment or other Rooftop Installations to be installed and evidence of
Landlord's approval thereof. In the event of an emergency, such notice shall
follow within five (5) days after access to the Antenna Area.

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

                                      -36-
<PAGE>

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

      G. Tenant shall have no right to sublet the Antenna Area.

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

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

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

      K. To the maximum extent permitted by law, all Rooftop Installations in
the Antenna Area shall be at the sole risk of Tenant, and Landlord shall have no
liability to Tenant in the event that any Rooftop Installations are damaged for
any reason.

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

      M. Tenant shall comply with all applicable laws, ordinances and
regulations in Tenant's use of the Antenna Area and the Antenna.

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

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

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

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

      R. (i) Tenant recognizes that Landlord may wish to (and Landlord hereby
reserves the right to) install a central Building system (the "Central Building
System") capable of, among other things, providing Tenant with the type of
service (to be) provided by Tenant's Rooftop Installations. If Landlord elects
to install the Central Building System, (i) Tenant shall, upon Landlord's

                                      -37-
<PAGE>

request and at Tenant's expense, remove its Rooftop Installations and other
Alterations (including any existing cabling) from the Building and repair any
damage caused their installation or removal, (ii) Tenant may, at Tenant's
expense and subject to the provisions of this Agreement (including, without
limitation, subparagraph P hereof), have access to and use (and tie into) the
Central Building System for the uses permitted hereunder, and (ii) commencing
upon Tenant's use of the Central Building System and continuing thereafter
throughout the term, the Yearly Rent payable hereunder shall be adjusted to be
that which is reasonably designated by Landlord from time to time based upon
Landlord's determination of the fair market value of the access rights to the
Central Building System granted herein.

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

      29.20 ROOFTOP MECHANICAL AREA.

      A. Tenant, at its cost, shall be permitted to install heating and
ventilating equipment ("HVAC Equipment") on the roof of the Building in the
locations shown on Exhibit 8. Tenant shall not install the HVAC Equipment
without obtaining Landlord's prior written approval, which approval shall not be
unreasonably withheld. If at any time Landlord, in its sole discretion, deems it
necessary, Tenant shall provide and install, at Tenant's sole cost and expense,
appropriate aesthetic screening, reasonably satisfactory to Landlord, for the
HVAC Equipment (the "Screening"). The HVAC Equipment, its appurtenances and
Screening, if any, shall be installed in accordance with the terms of this Lease
(including, without limitation, Articles 12 and 13 hereof) and Landlord's
approval of the precise location of the HVAC Equipment on the roof of the
Building (such area on the roof, as designated by Landlord, being referred to
herein as the "Rooftop Mechanical Area"), the manner in which the HVAC Equipment
is lifted to, and installed on, the roof of the Building, and the manner in
which the HVAC Equipment is connected to the Premises.

      B. Landlord agrees that Tenant shall have access to the roof of the
Building and the Rooftop Mechanical Area for the purpose of installing,
maintaining, repairing and removing the HVAC Equipment, the appurtenances and
the Screening, if any, all of which shall be performed by Tenant or Tenant's
authorized representative or contractors, which shall be approved by Landlord,
at Tenant's sole cost and risk. Tenant shall give Landlord reasonable written
notice to exercising its right of access to the roof; provided however, that if
any emergency requiring Tenant to exercise its roof access rights occurs at any
time when Landlord does not provide a security guard at the Complex twenty-four
(24) hours per, seven (7) days per week, then Tenant may exercise its roof
access rights immediately at the time of such emergency provided that Tenant
notifies Landlord of such access as soon as possible in the circumstances. It is
agreed, however, that only authorized engineers, employees or properly
authorized contractors of Tenant, or persons under their direct supervision,
will be permitted to have access to the roof of the Building and the Rooftop
Mechanical Area. Tenant further agrees to exercise firm control over the people
requiring access to the roof of the Building and the Rooftop Mechanical Area in
order to keep to a minimum the number of people having access to the roof of the
Building and the Rooftop Mechanical Area and the frequency of their visits.

      C. Tenant shall be responsible for the cost of all electricity consumed in
connection with the operation of the HVAC Equipment and for the cost of
installing a submeter, if required by Landlord, to measure such electrical
consumption. Tenant, at its sole cost and expense, shall procure and maintain in
full force and effect, a contract (the "Service Contract") for the service,
maintenance, repair and replacement of the HVAC Equipment with a HVAC service
and maintenance contracting firm reasonably acceptable to Landlord. Tenant shall
follow all reasonable recommendations of said contractor for the maintenance,
repair and replacement of the HVAC Equipment. The Service Contract shall provide
that the contractor shall perform inspections of the HVAC Equipment at intervals
of not less than three (3) months and that having made such inspections, said
contractor shall furnish a complete report of any defective conditions found to
be existing with respect to the HVAC Equipment, together with any
recommendations for maintenance, repair and/or replacement thereof. Said report
shall be furnished to Tenant with a copy to Landlord.

      D. The installation, maintenance, operation and removal of the HVAC
Equipment, the appurtenances and the Screening, if any, is not permitted to
damage the Building or the roof thereof, or interfere with the use of the
Building and roof by Landlord. Tenant agrees to be responsible for any damage
caused to the roof or any other part of the Building, which may be caused by
Tenant or any of its agents or representatives. Tenant agrees to maintain all of
the Tenant's equipment placed on or about the roof or in any other part of the
Building in proper operating condition and maintain same in satisfactory
condition as to appearance and safety, as

                                      -38-
<PAGE>

reasonably determined by Landlord. Such maintenance and operation shall be
performed in a manner to avoid any interference with Landlord. Tenant agrees
that at all times during the Term, it will keep the roof of the Building and the
Rooftop Mechanical Area free of all trash or waste materials produced by Tenant
or any Tenant Entities or contractors.

      E. The HVAC Equipment, appurtenances, and Screening, if any, shall remain
the property of Tenant until the expiration or earlier termination of this Lease
or Tenant's right to possession of the Premises, at which time they shall become
the property of Landlord; provided, however, that Landlord may, at Landlord's
option, require the Tenant, at Tenant's expense, to remove the HVAC Equipment,
appurtenances and/or Screening and restore the affected area(s) to the condition
they were in prior to installation of such items, ordinary wear and tear
excepted, including, without limitation, the patching of any holes in the roof
membrane to match, as closely as possible, the color surrounding the area where
the HVAC Equipment, appurtenances and Screening were attached. If Tenant fails
to remove such items and/or perform such restoration work, Landlord shall be
entitled to do so, at Tenant's cost.

      F. Tenant must provide Landlord with prior written notice of any
installation, removal or repair on the roof of the Building and coordinate such
work with Landlord in order to avoid voiding or otherwise adversely affecting
any warranties granted to Landlord with respect to the roof. If necessary,
Tenant, at its sole cost and expense, shall retain any contractor having a then
existing warranty in effect on the roof to perform such work (to the extent that
it involves the roof), or, at Tenant's option, to perform such work in
conjunction with Tenant's contractor. If Landlord contemplates roof repairs that
could affect Tenant's HVAC Equipment, Landlord shall formally notify Tenant at
least thirty (30) days in advance (except in cases of an emergency) prior to the
commencement of such contemplated work in order to allow Tenant to make other
arrangements for such service.

      G. Tenant specifically acknowledges and agrees that the terms and
conditions of Article 15 of this Lease shall apply with full force and effect to
the Rooftop Mechanical Area.

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

LANDLORD:                                   TENANT:
ONE KENDALL SQUARE ASSOCIATES, LLC,         IDENIX PHARMACEUTICALS, INC.
a Delaware limited liability company

By: One Kendall Square Mezzanine, LLC,
    its sole member

    By: One Kendall Square Investors, LLC
        its sole member

        By: Lincoln-One Kendall Square, LLC
            its administrative member

            By: /s/ W. Frank Cofer       By: /s/ Andrea Corcoran, Exec. VP Legal
                _______________________      ___________________________________
                  Name: W. Frank Cofer          (Name)           (Title)
                  Title: Vice President         Hereunto Duly Authorized

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

COMMONWEALTH, DISTRICT OR
STATE OF

COUNTY OF

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

                               /s/ Cynthia B. Gayne
                              __________________________

                                      -39-
<PAGE>

                                   Notary Public
                                   My Commission Expires: September 17, 2010
                                                          __________________

COMMONWEALTH OF MASSACHUSETTS

COUNTY OF SUFFOLK

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

                                   ______________________________________
                                   Notary Public
                                   My Commission Expires: _______________

COMMONWEALTH OF VIRGINIA

COUNTY OF ARLINGTON

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

                                    Caifa Knox
                                   _______________________________________
                                   Notary Public
                                   My Commission Expires: January 31, 2009
                                                          ________________

                                      -40-<PAGE>
                                                                    Exhibit 10.2

                          Idenix Pharmaceuticals, Inc.

                        Incentive Stock Option Agreement
                     Granted Under 2005 Stock Incentive Plan

1.    Grant of Option.

      This agreement evidences the grant by Idenix Pharmaceuticals, Inc., a
Delaware corporation (the "Company"), on ______, 200[ ] (the "Grant Date") to
[______] (the "Participant"), of an option to purchase (the "Option"), in whole
or in part, on the terms provided herein and in the Company's 2005 Stock
Incentive Plan (the "Plan"), a total of [______] shares (the "Shares") of common
stock, $.001 par value per share, of the Company ("Common Stock") at $[______]
per Share. Unless earlier terminated, this option shall expire at 5:00 p.m.,
Eastern time, on [_______] (the "Final Exercise Date").

      It is intended that the option evidenced by this agreement shall be an
incentive stock option as defined in Section 422 of the Internal Revenue Code of
1986, as amended, and any regulations promulgated thereunder (the "Code").
Except as otherwise indicated by the context, the term "Participant", as used in
this option, shall be deemed to include any person who acquires the right to
exercise this option validly under its terms.

2.    Vesting Schedule.

      This Option will become exercisable ("vest") ratably on a monthly basis
over a period of 48 months beginning of the last day of the month in which the
grant occurs and continuing thereafter on the last day of each of the next 47
successive months.

      The right of exercise shall be cumulative so that to the extent the Option
is not exercised in any period to the maximum extent permissible it shall
continue to be exercisable, in whole or in part, with respect to all Shares for
which it is vested until the earlier of the Final Exercise Date or the
termination of this Option under Section 3 hereof or the Plan.

3.    Exercise of Option.

      (a) Form of Exercise. Each election to exercise this Option shall be in
writing, signed by the Participant, and received by the Company at its principal
office, accompanied by this agreement, and payment in full in the manner
provided in the Plan. The Participant may purchase less than the number of
shares covered hereby, provided that no partial exercise of this Option may be
for any fractional share or for fewer than ten whole shares.

      (b) Continuous Relationship with the Company Required. Except as otherwise
provided in this Section 3, this Option may not be exercised unless the
Participant, at the time he or she exercises this option, is, and has been at
all times since the Grant Date, an employee, officer or director of, or
consultant or advisor to, the Company or any parent or subsidiary of the Company
as defined in Section 424(e) or (f) of the Code (an "Eligible Participant").

      (c) Termination of Relationship with the Company. If the Participant
ceases to be an Eligible Participant for any reason, then, except as provided in
paragraphs (d) and (e) below, the right to exercise this Option shall terminate
180 days after such cessation (but in no event after the Final Exercise Date),
provided that this Option shall be exercisable only to the extent that the
Participant was entitled to
<PAGE>
exercise this Option on the date of such cessation. Notwithstanding the
foregoing, if the Participant, prior to the Final Exercise Date, violates the
non-competition or confidentiality provisions of any employment contract,
confidentiality and nondisclosure agreement or other agreement between the
Participant and the Company, the right to exercise this Option shall terminate
immediately upon occurrence of such violation.

      (d) Exercise Period Upon Death or Disability. If the Participant dies or
becomes disabled (within the meaning of Section 22(e)(3) of the Code) prior to
the Final Exercise Date while he or she is an Eligible Participant and the
Company has not terminated such relationship for "cause" as specified in
paragraph (e) below, this Option shall be exercisable, within the period of one
year following the date of death or disability of the Participant, by the
Participant (or in the case of death by an authorized transferee), provided that
this Option shall be exercisable only to the extent that this Option was
exercisable by the Participant on the date of his or her death or disability,
and further provided that this Option shall not be exercisable after the Final
Exercise Date.

      (e) Discharge for Cause. If the Participant, prior to the Final Exercise
Date, is discharged by the Company for "cause" (as defined below), the right to
exercise this Option shall terminate immediately upon the effective date of such
discharge. "Cause" shall mean willful misconduct by the Participant or willful
failure by the Participant to perform his or her responsibilities to the Company
(including, without limitation, breach by the Participant of any provision of
any employment, consulting, advisory, nondisclosure, non-competition or other
similar agreement between the Participant and the Company), as determined by the
Company, which determination shall be conclusive. The Participant shall be
considered to have been discharged for "Cause" if the Company determines, within
30 days after the Participant's resignation, that discharge for cause was
warranted.

4.    Tax Matters.

      (a) Withholding. No Shares will be issued pursuant to the exercise of this
Option unless and until the Participant pays to the Company, or makes provision
satisfactory to the Company for payment of, any federal, state or local
withholding taxes required by law to be withheld in respect of this Option.

      (b) Disqualifying Disposition. If the Participant disposes of Shares
acquired upon exercise of this Option within two years from the Grant Date or
one year after such Shares were acquired pursuant to exercise of this Option,
the Participant shall notify the Company in writing of such disposition.

5.    Nontransferability of Option.

      This Option may not be sold, assigned, transferred, pledged or otherwise
encumbered by the Participant, either voluntarily or by operation of law, except
by will or the laws of descent and

                                     - 2 -
<PAGE>
distribution, and, during the lifetime of the Participant, this Option shall be
exercisable only by the Participant.

6.    Provisions of the Plan.

      This Option is subject to the provisions of the Plan, a copy of which is
furnished to the Participant with this Option.

      IN WITNESS WHEREOF, the Company has caused this agreement to be executed
under its corporate seal by its duly authorized officer. This agreement shall
take effect as a sealed instrument.

                                          IDENIX PHARMACEUTICALS, INC.

Dated: _________                          By:__________________________________

                                                Name:__________________________
                                                Title:_________________________

                                     - 3 -
<PAGE>
                            PARTICIPANT'S ACCEPTANCE

      The undersigned hereby accepts the foregoing Option and agrees to the
terms and conditions thereof. The undersigned hereby acknowledges receipt of a
copy of the Company's 2005 Stock Incentive Plan.

                                          PARTICIPANT:

                                          _____________________________________

                                          Address: ____________________________

                                                   ____________________________

                                     - 4 -

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00086-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00086-of-00352.parquet"}]]