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                                                                   EXHIBIT 10.08



                               THE CLARK BUILDING

                            Cambridge, Massachusetts







                                    LANDLORD
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                       FOREST CITY 38 SIDNEY STREET, INC.



                                     TENANT
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                                 ACUSPHERE, INC.
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                               THE CLARK BUILDING

                            Lease to Acusphere, Inc.

                                Table of Contents

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ARTICLE I - RECITALS AND DEFINITIONS............................................

         Section 1.1 Recitals ..................................................  1
         Section 1.2 Definitions ...............................................  1

ARTICLE II - PREMISES AND TERM..................................................

         Section 2.1 Premises ..................................................  2
         Section 2.2 Appurtenant Rights ........................................  3
         Section 2.3 Landlord's Reservations ...................................  3
         Section 2.4 Parking ...................................................  3
         Section 2.5 Commencement Date .........................................  4
         Section 2.6 Extension Option ..........................................  4

ARTICLE III - RENT AND OTHER PAYMENTS...........................................

         Section 3.1 Annual Fixed Rent .........................................  4
         Section 3.2 Real Estate Taxes .........................................  5
         Section 3.3 Operating Expenses.........................................  6
         Section 3.4 Other Utility Charges .....................................  8
         Section 3.5 Above-standard Services ...................................  9
         Section 3.6 No Offsets ................................................  9
         Section 3.7 Net Lease .................................................  9

ARTICLE IV - ALTERATIONS .......................................................

         Section 4.1 Consent Required for Tenant's Alterations .................  9
         Section 4.2 Ownership of Alterations . ................................ 10
         Section 4.3 Construction Requirements for Alterations ................. 10
         Section 4.4 Payment for Tenant Alterations ............................ 11

ARTICLE V - RESPONSIBILITY FOR CONDITION OF BUILDING AND PREMISES...............

         Section 5.1 Maintenance of Building and Common Areas by Landlord ...... 11
         Section 5.2 Maintenance of Premises by Tenant ......................... 11
         Section 5.3 Delays in Landlord's Services ............................. 12
         Section 5.4 Landlord's and Tenant's Covenants Regarding Environmental
                        Matters ................................................ 12
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                                       (i)
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ARTICLE VI - TENANT COVENANTS ..................................................

         Section 6.1 Permitted Uses ............................................ 13
         Section 6.2 Laws and Regulations ...................................... 14
         Section 6.3 Rules and Regulations ..................................... 14
         Section 6.4 Safety Compliance ......................................... 14
         Section 6.5 Landlord's Entry .......................................... 15
         Section 6.6 Floor Load ................................................ 15
         Section 6.7 Personal Property Tax ..................................... 15
         Section 6.8 Assignment and Subleases .................................. 15

ARTICLE VII - INDEMNITY AND INSURANCE ..........................................

         Section 7.1 Indemnity ................................................. 17
         Section 7.2 Liability Insurance ....................................... 17
         Section 7.3 Personal Property at Risk ................................. 18
         Section 7.4 Landlord's Insurance ...................................... 18
         Section 7.5 Waiver of Subrogation ..................................... 18

ARTICLE VIII - CASUALTY AND EMINENT DOMAIN .....................................

         Section 8.1 Restoration Following Casualties .......................... 19
         Section 8.2 Landlord's Termination Election ........................... 19
         Section 8.3 Tenant's Termination Election ............................. 19
         Section 8.4 Casualty at Expiration of Lease ........................... 20
         Section 8.5 Eminent Domain ............................................ 20
         Section 8.6 Rent After Casualty or Taking ............................. 20
         Section 8.7 Temporary Taking .......................................... 20
         Section 8.8 Taking Award .............................................. 21

ARTICLE IX - DEFAULT ...........................................................

         Section 9.1 Tenant's Default .......................................... 21
         Section 9.2 Damages ................................................... 22
         Section 9.3 Cumulative Rights ......................................... 22
         Section 9.4 Landlord's Self-Help ...................................... 23
         Section 9.5 Enforcement Expenses ...................................... 23
         Section 9.6 Late Charges and Interest on Overdue Payments ............. 23
         Section 9.7 Landlord's Right to Notice and Cure ....................... 24

ARTICLE X - MORTGAGEES' AND GROUND LESSORS' RIGHTS .............................

         Section 10.1 Subordination ............................................ 24
         Section 10.2 Prepayment of Rent Not to Bind Mortgagee ................. 24
         Section 10.3 Tenant's Duty to Notify Mortgagee; Mortgagee's Ability to
                         Cure .................................................. 24
         Section 10.4 Estoppel Certificates .................................... 25
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                                      (ii)
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ARTICLE XI - MISCELLANEOUS ...................................................

       SECTION 11.1  Notice of Lease .........................................26
       SECTION 11.2  Notices..................................................26
       SECTION 11.3  Successors and Limitation on Liability of the Landlord...26
       SECTION 11.4  Waivers by the Landlord .................................26
       SECTION 11.5  Acceptance of Partial Payments of Rent ..................27
       SECTION 11.6  Interpretation and Partial Invalidity ...................27
       SECTION 11.7  Quiet Enjoyment .........................................27
       SECTION 11.8  Brokerage ...............................................27
       SECTION 11.9  Surrender of Premises and Holding Over ..................27
       SECTION 11.10 Ground Lease . ..........................................28
       SECTION 11.11 Security Deposit ........................................28
       SECTION 11.12 Financial Reporting .....................................29
       SECTION 11.13 Cambridge Employment Plan ...............................29
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EXHIBIT A      Basic Lease Terms
EXHIBIT B      Legal Description
EXHIBIT B-1    Location of Premises
EXHIBIT C      Work Letter
EXHIBIT C-1    Tenant's Final Plans
EXHIBIT D      Standard Services
EXHIBIT E      Rules and Regulations

EXHIBIT G      Tenant System Allocations and Capacities

                                     (iii)
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                                      LEASE



                                    ARTICLE I

                            RECITALS AND DEFINITIONS

Section 1.1 - Recitals.

         This Lease (this "Lease") is entered into as of April 18, 1995
by and between Forest City 38 Sidney Street, Inc. (the "Landlord"), an Ohio
corporation and Acusphere, Inc. (the "Tenant"), a Delaware corporation.

         In consideration of the mutual covenants herein set forth, the Landlord
and the Tenant do hereby agree to the terms and conditions set forth in this
Lease.

Section 1.2 - Definitions.

         The following Terms, have the meanings indicated or referred to below:

         "Additional Rent" means all charges payable by the Tenant pursuant to
this Lease other than Annual Fixed Rent, including without implied limitation
the Tenant's parking charges as provided in Section 2.4; the Tenant's Tax
Expense Allocable to the Premises as provided in Section 3.2; the Tenant's
Operating Expenses Allocable to the Premises in accordance with Section 3.3;
amounts payable for special services pursuant to Section 3.5; costs for
alterations or additions to the Original Premises exceeding the Tenant's
Allowance pursuant to the Work Letter; the Landlord's share of any sublease or
assignment proceeds pursuant to Section 6.8.

         "Annual Fixed Rent" - See Exhibit A, and Section 3.1.

         "Building" means The Clark Building located at 38 Sidney Street,
Cambridge, Massachusetts in which the Premises are located.

         "Commencement Date" - See Section 2.5.

         "Common Building Areas" means those portions of the Building which are
not part of the Premises and to which the Tenant has appurtenant rights pursuant
to Section 2.2.

         "External Causes" means collectively, (i) Acts of God, war, civil
commotion, fire, flood or other casualty, strikes or other extraordinary labor
difficulties, shortages of labor or materials or equipment in the ordinary
course of trade, government order or regulations or other cause not reasonably
within
<PAGE>
the Landlord's control and not due to the fault or neglect of the Landlord, and
(ii) any act, failure to act or neglect of the Tenant or the Tenant's servants,
agents, employees, licensees or any person claiming by, through or under the
Tenant, which delays the Landlord in the performance of any act required to be
performed by the Landlord under this Lease.

         "Initial Term" - See Exhibit A.

         "Land" means the parcel of land situated in Cambridge, Massachusetts,
described in Exhibit B.

         "Landlord's Original Address" - See Exhibit A.

         "Lease Year" means each period of one year during the Term commencing
on the Commencement Date or on any anniversary thereof.

         "Original Premises" - See Exhibit A.

         "Permitted Uses" - See Exhibit A.

         "Premises" means that portion of the Building which the Tenant is
leasing at any given time pursuant to the provisions of this Lease. See Exhibit
A and Section 2.1.

         "Property" means the Land and the Building.

         "Tenant's Original Address" - See Exhibit A.

         "Term" means the Initial Term as it may be extended by written
agreement between the Landlord and the Tenant.

         "University Park" means the area in Cambridge, Massachusetts, bounded
on the North side by Massachusetts Avenue, on the East side by Landsdowne, Cross
and Purrington Streets, on the South side by Pacific Street and on the West side
by Brookline Street.

         "Work Letter" means the letter agreement of even date herewith between
the Landlord and Tenant relating to the construction of leasehold improvements
in the Premises attached hereto as Exhibit C.

                                   ARTICLE II

                                PREMISES AND TERM

Section 2.1 - Premises.

         The Landlord hereby leases to the Tenant, and the Tenant hereby 1 eases
from the Landlord, for the Term, the Original Premises. The Premises shall
exclude the entry and main lobby of the Building, first floor elevator lobby,
first floor mail room, the common stairways and stairwells, elevators and
elevator wells, boiler room, sprinklers, sprinkler rooms, elevator rooms,
mechanical rooms, loading and receiving areas, electric and telephone closets,
janitor closets,


                                       2
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and pipes, ducts, conduits, wires and appurtenant fixtures and equipment serving
exclusively or in common other parts of the Building. If the Premises at any
time includes less than the entire rentable floor area of any floor of the
Building, the Premises shall also exclude the common corridors, vestibules,
walkways, elevator lobby and toilets located on such floor. The Tenant
acknowledges that, except as expressly set forth in this Lease, there have been
no representations or warranties made by or on behalf of the Landlord with
respect to the Premises, the Building or the Property or with respect to the
suitability of any of them for the conduct of the Tenant's business. The taking
of possession of the Premises by the Tenant shall conclusively establish that
the Premises and the Building were at such time in satisfactory condition, order
and repair.

Section 2.2 - Appurtenant Rights.

         The Tenant shall have, as appurtenant to the Premises, the nonexclusive
right to use in common with others, subject to reasonable rules of general
applicability to occupants of the Building from time to time made by the
Landlord of which the Tenant is given notice: (i) the entry, vestibules and main
lobby of the Building, first floor mailroom, the common stairways, elevators,
elevator wells, boiler room, elevator rooms, sprinkler rooms, mechanical rooms,
electric and telephone closets, janitor closets and the pipes, sprinklers,
ducts, conduits, wires and appurtenant fixtures and equipment serving the
Premises in common with others, (ii) common walkways and driveways necessary or
reasonably convenient for access to the Building, (iii) access to loading area
and freight elevator subject to Rules and Regulations then in effect, and (iv)
if the Premises at any time include less than the entire rentable floor area of
any floor, the common toilets, corridors, vestibules, bridges and walkways, and
elevator lobby of such floor.

Section 2.3 - Landlord's Reservations.

         The Landlord reserves the right from time to time, without unreasonable
interference with the Tenant's use: (i) to install, use, maintain, repair,
replace and relocate for service to the Premises and other parts of the
Building, or either, pipes, ducts, conduits, wires and appurtenant fixtures and
equipment, wherever located in the Premises or the Building, and (ii) to alter
or relocate any other common facility, provided that substitutions are
substantially equivalent or better.

Section 2.4 - Parking.

         The Landlord shall provide and the Tenant shall pay for parking
privileges for use by the Tenant's employees and business invitees and visitors
in accordance with Exhibit A. The Landlord shall have the right to designate
from time to time, and to change from time to time, the location within
University Park that shall be used for the parking of the Tenant's automobiles.
The Landlord may cause to be constructed within University Park a parking garage
or garages (a "Garage") to serve the Building and other buildings. When a Garage
is completed, the Landlord shall have the right to relocate all or any portion
of the Tenant's parking rights to a Garage. The Tenant's parking privileges may
be on a nonexclusive basis. The Tenant agrees that it and all persons claiming


                                       3
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by, through and under it, shall at all times abide by the reasonable rules and
regulations promulgated by the Landlord with respect to the use of the parking
facilities provided by the Landlord pursuant to this Lease.

         Except as otherwise provided in Exhibit A, the Tenant shall pay to the
Landlord for the Tenant's parking privileges the monthly rent at which the
Landlord from time to time offers to make parking privileges available to
tenants and other users of such parking facilities which pay rent therefor.
Monthly parking charges shall constitute Additional Rent and shall be payable at
the time and in the fashion in which Annual Fixed Rent under this Lease is
payable, or at the option of the Landlord, the Tenant shall enter into a
separate lease agreement for such parking rights for a period which shall have
the same expiration date as the Term and which, if this Lease provides for
options on the part of the Tenant to extend, shall be automatically extended
upon the exercise of any of such options.

Section 2.5 - Commencement Date.

         "Commencement Date" means, for any portion of the Premises designated
in the Work Letter for separate completion, the date which is the later of (i)
the earlier of May 1, 1995; or the date on which the Tenant occupies any portion
of such space or (ii) date work is completed by Landlord per Work Letter
(subject to delay). If work is not completed within thirty (30) days after May
1, 1995, Tenant shall have the right to terminate its obligations hereunder.

Section 2.6 - Extension Option.

         Provided that there has been no Event of Default on the part of the
Tenant, other than any which have been waived by the Landlord, the Tenant shall
have the right to extend the Term hereof for one (1) period of eighteen (18)
months (the "Extension Term"), such option to extend to be exercised by the
giving of notice by the Tenant to the Landlord at least six (6) months prior to
the expiration of the then current Term. Upon the giving of such notice, this
Lease and the Term hereof shall be extended, for an additional term of eighteen
(18) months, without the necessity for the execution of any additional
documents. Time is of the essence in the giving of such notice.

                                   ARTICLE III

                             RENT AND OTHER PAYMENTS

Section 3.1 - Annual Fixed Rent.

         From and after the Commencement Date, the Tenant shall pay, without
notice or demand, monthly installments of one-twelfth (1/12th) of the Annual
Fixed Rent in effect and applicable to the Premises in advance for each full
calendar month of the Term and of the corresponding fraction of said one-twelfth
(1/12th) for any fraction of a calendar month at the beginning or end of the
Term. The Annual Fixed Rent applicable to the Premises during the Initial Term
shall be as set forth in Exhibit A.


                                       4
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Section 3.2 - Real Estate Taxes.

         From and after the Commencement Date, during the Term, the Tenant shall
pay to the Landlord, as Additional Rent, the Tenant's Tax Expenses Allocable to
the Premises, (as such term is hereinafter defined) in accordance with this
Section 3.2. The terms used in this Section 3.2 are defined as follows:

         (a)      "Tax Year" means the 12-month period beginning July 1 each
                  year or if the appropriate governmental tax fiscal period
                  shall begin on any date other than July 1, such other date.

         (b)      "The Tenant's Tax Expense Allocable to the Premises" means (i)
                  that portion of the Landlord's Tax Expenses for a Tax Year
                  which bears the same proportion thereto as the Rentable Floor
                  Area of the Premises (from time to time) bears to the Total
                  Rentable Floor Area of the Building and (ii) in the event that
                  the Premises are improved to a standard which is higher than
                  other portions of the Property, such portion of the Real
                  Estate Taxes on the Property with respect to any Tax Year as
                  is appropriate so that the Tenant bears the portion of the
                  Real Estate Taxes which are properly allocable to the
                  Premises, as reasonably determined by Landlord based on
                  information with respect to the assessment process made
                  available by the assessing authorities. Landlord represents
                  that the improvements to date have not resulted in the
                  Premises being disproportionately assessed in real estate
                  taxes.

         (c)      "The Landlord's Tax Expenses" with respect to any Tax Year
                  means the aggregate Real Estate Taxes on the Property with
                  respect to that Tax Year, reduced by any abatement receipts
                  with respect to that Tax Year.

         (d)      "Real Estate Taxes" means all taxes and special assessments of
                  every kind and nature assessed by any governmental authority
                  on the applicable property and reasonable expenses of any
                  proceedings for abatement of such taxes or special assessments
                  to be included shall be limited to the amount of the
                  installment (plus any interest thereon) of such special tax or
                  special assessment (which shall be payable over the longest
                  period permitted by law) required to be paid during the Tax
                  Year in respect of which such taxes are being determined.
                  There shall be excluded from such taxes all income, estate,
                  succession, inheritance, excess profit, franchise and transfer
                  taxes; provided, however, that if at any time during the Term
                  the present system of ad valorem taxation of' real property
                  shall be changed so that in lieu of the whole or any part of
                  the ad valorem tax on real property, there shall be assessed
                  on the Landlord a capital levy or other tax on the gross rents
                  received with respect to the Property, or a Federal, State,
                  County, Municipal, or other local income, franchise, excise or
                  similar tax, assessment, levy or charge (distinct from any now
                  in effect) based, in whole or in part, upon any such gross
                  rents, then any and all of such taxes, assessments, levies or
                  charges, to the extent so based, shall be deemed to be
                  included within the term "Real Estate Taxes."


                                       5
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         Payments by the Tenant on account of the Tenant's Tax Expenses
Allocable to the Premises shall be made monthly at the time and in the fashion
herein provided for the payment of Annual Fixed Rent and shall be in an amount
of the greater of (i) one-twelfth (1/12th) of the Tenant's Tax Expenses
Allocable to the Premises for the current Tax Year as reasonably estimated by
the Landlord, or (ii) an amount estimated by any ground lessor of the Land or
holder of a first mortgage on the Property, to be sufficient, if paid monthly,
to pay the Landlord's Tax Expenses on the dates due to the taxing authority.

         Not later than ninety (90) days after the Landlord's Tax Expenses are
determinable for the first Tax Year of the Term or fraction thereof and for each
succeeding Tax Year or fraction thereof during the Term, the Landlord shall
render the Tenant a statement in reasonable detail showing for the preceding
year or fraction thereof, as the case may be, real estate taxes on the Property,
and any abatements or refunds of such taxes. Expenses incurred in obtaining any
tax abatement or refund may be charged against such tax abatement or refund
before the adjustments are made for the Tax Year. If at the time such statement
is rendered it is determined with respect to any Tax Year, that the Tenant has
paid (i) less than the Tenant's Tax Expenses Allocable to the Premises or (ii)
more than the Tenant's Tax Expenses Allocable to the Premises, then, in the case
of (i) the Tenant shall pay to the Landlord, as Additional Rent, within fifteen
(15) days of such statement the amount of such underpayment and, in the case of
(ii) the Landlord shall credit the amount of such overpayment against the
monthly installments of the Tenant's Tax Expenses Allocable to the Premises next
thereafter coming due (or refund such overpayment if the Term has expired and
the Tenant has no further obligation to the Landlord).

         To the extent that real estate taxes shall be payable to the taxing
authority in installments with respect to periods less than a Tax Year, the
statement to be furnished by the Landlord shall be rendered and payments made on
account of such installments. Notwithstanding the foregoing provisions, no
decrease in Landlord's Tax Expenses with respect to any Tax Year shall result in
a reduction of the amount otherwise payable by Tenant if and to the extent said
decrease is attributable to vacancies in the Building, rather than to a
reduction in the assessed value of the Property as a whole or a reduction in the
tax rate. Landlord shall, upon Tenant's request therefor, provide Tenant with
copies of all applicable tax bills, statements, records and the like, as well as
copies of Landlord's calculations and all other relevant information.

Section 3.3 - Operating Expenses.

         From and after the Commencement Date, during the Term the Tenant shall
pay to the Landlord, as Additional Rent, the Tenant's Operating Expenses
Allocable to the Premises, as hereinafter defined, in accordance with this
Section 3.3. The terms used in this Section 3.3 are defined as follows:

         (a)      "The Tenant's Operating Expenses Allocable to the Premises"
                  means that portion of the Operating Expenses for the Property
                  which bears the same proportion thereto as the Rentable Floor
                  Area of the Premises bears to the Total Rentable Floor Area of
                  the Building.


                                       6
<PAGE>
         (b)      "Operating Expenses for the Property" means Landlord's cost of
                  operating, cleaning, maintaining and repairing the Property,
                  the parking lots and garages for tenants in the Building and
                  the roads, driveways and walkways for providing access to the
                  Building and such parking facilities and shall include without
                  limitation, the cost of services on Exhibit D, premiums for
                  insurance carried pursuant to Section 7.4; the amount
                  deductible from any insurance claim of the Landlord;
                  compensation and all fringe benefits, worker's compensation
                  insurance premiums and payroll taxes paid to, for or with
                  respect to all persons directly engaged in the operating,
                  maintaining or cleaning of the Property and such parking
                  facilities; interior landscaping and maintenance, steam,
                  water, sewer, gas, oil, electricity, telephone and other
                  utility charges (excluding such utility charges either
                  separately metered or separately chargeable to tenants for
                  additional or special services); cost of providing conditioned
                  water for HVAC services; cost of building and cleaning
                  supplies; rental costs for equipment used in the operating,
                  cleaning, maintaining or repairing of the Property, or the
                  applicable fair market rental charges in the case of equipment
                  owned by the Landlord; cost of cleaning; cost of maintenance,
                  repairs and replacements (other than repairs and replacements
                  reimbursed from contractors under guarantees or made by the
                  Landlord pursuant to the Work Letter); cost of snow removal;
                  cost of landscape maintenance; security services; payments
                  under service contracts with independent contractors,
                  management fees at reasonable rates consistent with the type
                  of occupancy and the service rendered; the cost of any capital
                  improvement made for the purpose of reducing operating
                  expenses or to comply with applicable law, which cost shall be
                  amortized in accordance with generally accepted accounting
                  principles, together with interest on the unamortized balance
                  at the base lending rate announced by a major commercial bank
                  designated by the Landlord, or such higher rate as may have
                  been paid by the Landlord on funds borrowed for the purpose of
                  constructing such capital improvements; charges allocated to
                  the Building for the operating, cleaning, maintaining and
                  repairing of University Park common areas and amenities; and
                  all other reasonable and necessary expenses paid in connection
                  with the operation, cleaning, maintenance and repair of the
                  Property. If, for any reason portions of the Rentable Area of
                  the Building not included in the Premises were not occupied by
                  tenants or the Landlord was not supplying all tenants with the
                  services being supplied under the Lease or any tenants in the
                  Building were supplied with a lesser level of standard
                  services than those supplied to the Tenant under this Lease,
                  Landlord's Operating Expenses for the Property shall include
                  the amounts reasonably determined by Landlord which would have
                  been incurred if all of the rentable area in the Building were
                  occupied and were supplied with the same level of standard
                  services as supplied to the Tenant under this Lease.

                                       7
<PAGE>
                  Operating Expenses for the Property shall not include the
                  following: the Landlord's Tax Expense; cost of repairs or
                  replacements (i) resulting from eminent domain takings, (ii)
                  to the extent reimbursed by insurance, (iii) resulting from
                  correcting defects in the work for which the Landlord is
                  obligated pursuant to the Work Letter, or (iv) required, above
                  and beyond ordinary periodic maintenance, to maintain in
                  serviceable condition the major structural elements of the
                  Building, including the roof, exterior walls and floor slabs;
                  replacement or contingency reserves; the cost of capital
                  improvements (other than as specifically provided for above);
                  ground lease rents or payment of debt obligations; legal and
                  other professional fees for matters not relating to the normal
                  administration and operation of the Property; promotional,
                  advertising, public relations or brokerage fees and
                  commissions paid in connection with services rendered for
                  securing or renewing leases. The Landlord's Operating Expenses
                  shall be reduced by the amount of any proceeds, payments,
                  credits or reimbursements which the Landlord receives from
                  sources other than tenants and which are applicable to such
                  Operating Expenses for the Property.

         Payments by the Tenants on account of the Tenant's Operating Expenses
Charge shall be made monthly at the time and in the fashion herein provided for
the payment of Annual Fixed Rent. The amount so to be paid to the Landlord shall
be an amount from time to time reasonably estimated by the Landlord to be
sufficient to aggregate a sum equal to the Tenant's Operating Expenses Charge
for each calendar year.

         Not later than ninety (90) days after the end of each calendar year or
fraction thereof during the Term or fraction thereof at the end of the Term, the
Landlord shall render the Tenant a statement in reasonable detail and according
to usual accounting practices certified by a representative of the Landlord,
showing for the preceding calendar year or fraction thereof, as the case may be,
the Operating Expenses for the Property and the Tenant's Operating Expenses
Allocable to the Premises. Said statement to be rendered to the Tenant also
shall show for the preceding calendar year or fraction thereof, as the case may
be, the amounts of Operating Expenses already paid by the Tenant. If at the time
such statement is rendered it is determined with respect to any calendar year,
that the Tenant has paid (i) less than the Tenant's Operating Expenses Allocable
to the Premises or (ii) more than the Tenant's Operating Expenses Allocable to
the Premises, then, in the case of (i) the Tenant shall pay to the Landlord, as
Additional Rent, within thirty (30) days of such statement the amounts of such
underpayment and, in the case of (ii) the Landlord shall credit the amount of
such overpayment against the monthly installments of the Tenant's Operating
Expenses Allocable to the Premises next thereafter coming due (or refund such
overpayment if the Term has expired and the Tenant has no further obligation to
the Landlord).

Section 3.4 - Other Utility Charges.

         During the Term, the Tenant shall pay directly to the provider of the
service, all separately metered charges for steam, heat, gas, electricity, fuel
and other services and utilities furnished to the Premises.


                                       8
<PAGE>
Section 3.5 - Above-standard Services.

         If the Tenant requests and the Landlord elects to provide any services
to the Tenant in addition to those described in Exhibit D, the Tenant shall pay
to the Landlord, as Additional Rent, the amount billed by Landlord for such
services at Landlord's standard rates as from time to time in effect. If the
Tenant has requested that such services be provided on a regular basis, the
Tenant shall, if requested by the Landlord, pay for such services at the time
and in the fashion in which Annual Fixed Rent under this Lease is payable.
Otherwise, the Tenant shall pay for such additional services within thirty (30)
days after receipt of an invoice from the Landlord. Landlord shall have the
right from time to time to inspect Tenant's utility meters and to install timers
thereon at Tenant's expense for purposes of monitoring above-standard service
usage. Tenant shall pay for such work within thirty (30) days after receipt of
an invoice from Landlord.

Section 3.6 - No Offsets.

         Annual Fixed Rent and Additional Rent shall be paid by the Tenant
without offset, abatement or deduction.

Section 3.7 - Net Lease.

         It is understood and agreed that this Lease is a net lease and that the
Annual Fixed Rent is absolutely net to the Landlord excepting only the
Landlord's obligations to pay any debt service or ground rent on the Property,
to provide the Landlord's services, and to pay the real estate taxes and
operating expenses which the Tenant is not required to pay under this Lease.

                                   ARTICLE IV

                                   ALTERATIONS

Section 4.1 - Consent Required for Tenant's Alterations.

         The Tenant shall not make alterations or additions to the Premises
except in accordance with the building standards from time to time in effect,
with construction rules and regulations from time to time promulgated by
Landlord and applicable to Tenants in the Building, and with plans and
specifications therefor first approved by the Landlord, which approval shall not
be withheld unreasonably. Landlord shall approve or disapprove of such plans
within ten (10) days of submittal or such plans shall be deemed approved. The
Landlord shall not be deemed unreasonable for withholding approval of any
alterations or additions which (i) involve or might affect any structural or
exterior element of the Building, any area or element outside of the Premises,
or any facility serving any area of the Building outside of the Premises or any
publicly accessible major interior features of the Building, (ii) will require
unusual expense to readapt the Premises to normal use unless the Tenant first
gives assurance acceptable to the Landlord that such readaptation will be made
prior to such termination without expense to the Landlord, or (iii) which would
not be compatible with


                                       9
<PAGE>
existing mechanical or electrical, plumbing, HVAC or other systems in the
Building, in each case, as reasonably determined by the Landlord.

Section 4.2 - Ownership of Alterations.

         All alterations and additions shall be part of the Building and owned
by the Landlord, unless, prior to installation, Landlord agrees Tenant may
remove such items or at the time of the termination of this Lease the Landlord
shall specify that the same must be removed. All movable equipment and
furnishings not attached to the Premises shall remain the property of the Tenant
and shall be removed by the Tenant upon termination or expiration of this Lease.
The Tenant shall repair any damage caused by the removal of any alterations,
additions or personal property from the Premises.

Section 4.3 - Construction Requirements for Alterations.

         All construction work by the Tenant shall be done in a good and
workmanlike manner employing only first-class materials and in compliance with
all applicable laws and all lawful ordinances, regulations and orders of
Governmental authority and insurers of the Building. The Landlord or Landlord's
authorized agent may (but without any implied obligation to do so) inspect the
work of the Tenant at reasonable times and shall give notice of observed
defects. All of the Tenant's alterations and additions and installation of
furnishings shall be coordinated with any work being performed by the Landlord
and in such manner as to maintain harmonious labor relations and not to damage
the Building or interfere with Building construction or operation and, except
for installation of furnishings, shall be performed by the Landlord's general
contractor or by contractors or workmen first approved by the Landlord, which
approval the Landlord agrees not to unreasonably withhold or delay. The Tenant,
before starting any work (1) shall receive and comply with Landlord's
construction rules and regulations and shall cause Tenant's contractors to
comply therewith, (2) shall secure all licenses and permits necessary therefor
and shall deliver to the Landlord a statement of the names of all its
contractors and subcontractors and the estimated cost of a labor and material to
be furnished by them and reasonable security satisfactory to the Landlord
protecting the Landlord against liens arising out of the furnishing of such
labor and material, (3) and cause each contractor to carry worker's compensation
insurance in statutory amounts covering all the contractors' and subcontractors'
employees and comprehensive general public liability insurance with such limits
as the Landlord may require reasonably, but in no event less than $1,000,000
(individual)/$3,000,000 (Occurrence) or in such other amounts as Landlord may
reasonably require covering personal injury and death and property damage (all
such insurance to be written in companies approved reasonably by the Landlord
and insuring the Landlord, such individuals and entities affiliated with the
Landlord as the Landlord may designate, and the Tenant as well as the
contractors and to contain a requirement for at least thirty (30) days' notice
to the Landlord prior to cancellation, nonrenewal or material change), and to
deliver to the Landlord certificates of all such insurance.


                                       10
<PAGE>
Section 4.4 - Payment for Tenant Alterations.

         The Tenant agrees to pay promptly when due the entire cost of any work
done on the Premises by the Tenant, its agents, employees or independent
contractors, and not to cause or permit any liens for labor or materials
performed or furnished in connection therewith to attach to the Premises or the
Property and promptly to discharge any such liens which may so attach. If any
such lien shall be filed against the Premises or the Property and the Tenant
shall fail to cause such lien to be discharged within ten (10) days after the
filing thereof, the Landlord may cause such lien to be discharged by payment,
bond or otherwise without investigation as to the validity thereof or as to any
offsets or defenses which the Tenant may have with respect to the amount
claimed. The Tenant shall reimburse the Landlord, as additional rent, for any
cost so incurred and shall indemnify and hold harmless the Landlord from and
against any and all claims, costs, damages, liabilities and expenses (including
attorneys' fees) which may be incurred or suffered by the Landlord by reason of
any such lien or its discharge.

                                    ARTICLE V

              RESPONSIBILITY FOR CONDITION OF BUILDING AND PREMISES

Section 5.1 - Maintenance of Building and Common Areas by Landlord.

         Except as otherwise provided in Article 8, the Landlord shall make such
repairs to the major structural elements of the Building, including the roof,
exterior walls and floor slabs as may be necessary to keep and maintain the same
in serviceable condition and maintain and make such repairs to the Common
Building Areas as may be necessary to keep them in good order, condition and
repair, including without limitation, the glass in the exterior walls of the
Building, and all mechanical systems and equipment serving the Building and not
exclusively serving the Premises. The Landlord shall further perform the
services on Exhibit D hereto. The Landlord shall in no event be responsible to
the Tenant for any condition in the Premises or the Building caused by an act or
neglect of the Tenant, or any invitee or contractor of the Tenant. Landlord's
costs in performing such services shall be reimbursed by the Tenant to the
extent provided in Section 3.3.

Section 5.2 - Maintenance of Premises by Tenant.

         The Tenant shall keep neat and clean and maintain in good order,
condition and repair the Premises and every part thereof and all Building and
mechanical equipment exclusively serving the Premises, reasonable wear and tear
excepted and further excepting those repairs for which the Landlord is
responsible pursuant to Section 5.1 and damage by fire or other casualty and as
a consequence of the exercise of the power of eminent domain and shall surrender
the Premises and all alterations and additions thereto, at the end of the Term,
in such condition, first removing all goods and effects of the Tenant and, to
the extent specified by the Landlord by notice to the Tenant, all alterations
and additions made by the Tenant and repairing any damage caused by such removal
and restoring the Premises and leaving them clean and neat. Mechanical equipment
shall be


                                       11
<PAGE>
maintained in accordance with the standards established by the Landlord, as
modified from time to time. Tenant shall, upon request, provide evidence
reasonably satisfactory to Landlord that it has available the necessary
expertise to properly conduct and carry out this responsibility, either through
persons employed by the company or through contracts with independent service
organizations, or a combination thereof. Alternatively, upon Tenant's request,
Landlord agrees to accept responsibility for the maintenance of mechanical
equipment exclusively service the Premises. All charges incurred by Landlord in
connection with such work, whether by independent organizations or in accordance
with reasonable rates assigned to employees of Landlord or Landlord's
affiliates, shall be promptly reimbursed by Tenant as Additional Rent. The
Tenant shall not permit or commit any waste, and the Tenant shall be responsible
for the cost of repairs which may be made necessary by reason of damages to
common areas in the building by the Tenant, or any of the contractors or
invitees of the Tenant.

Section 5.3 - Delays in Landlord's Services.

         The Landlord shall not be liable to the Tenant for any compensation or
reduction of rent by reason or inconvenience or annoyance or for loss of
business arising from the necessity of the Landlord or its agents entering the
Premises for any purposes authorized in this Lease, or for repairing the
Premises or any portion of the Building. In case the Landlord is prevented or
delayed from making any repairs, alterations or improvements, or furnishing any
services or performing any other covenant or duty to be performed on the
Landlord's part, by reason of any External Cause, the Landlord shall not be
liable to the Tenant therefor, nor, except as expressly otherwise provided in
this Lease, shall the Tenant be entitled to any abatement or reduction of rent
by reason thereof, nor shall the same give rise to a claim in the Tenant's favor
that such failure constitutes actual or constructive, total or partial, eviction
from the Premises.

         The Landlord reserves the right to stop any service or utility system
when necessary by reason of accident or emergency, until necessary repairs have
been completed; provided, however, that in each instance of stoppage, the
Landlord shall exercise reasonable diligence to eliminate the cause thereof.
Except in case of emergency repairs, the Landlord will give the Tenant
reasonable advance notice of any contemplated stoppage and will use reasonable
efforts to avoid unnecessary inconvenience to the Tenant by reason thereof. In
no event shall the Landlord have any liability to the Tenant for the
unavailability of heat, light or any utility or service to be provided by the
Landlord to the extent that such unavailability is caused by External Causes
unless such interruption or stoppage extends beyond six (6) months, in which
event Tenant shall have the right to terminate this Lease.

Section 5.4 - Landlord's and Tenant's Covenants Regarding
              Environmental Matters.

         Landlord affirms that, to the best of its knowledge, the Building and
its systems are free of any environmental contamination. The Landlord has
initiated, and covenants and agrees to continue to conduct, an indoor
environmental quality monitoring and management program with respect to the
Building. Tenant, and its employees, agents and contractors, shall cooperate in
the ongoing conduct of this program, and shall participate and comply with the
requirements and recommendations of this program to the extent such requirements
and



                                       12
<PAGE>
recommendations pertain to the operations or the maintenance responsibilities of
the Tenant. If, during the lease term commencing with the Base Rent Commencement
Date, the Tenant's officers and employees in the Premises suffer from ailments
or illness of any kind, which the Tenant believes in good faith to result from
environmental conditions which exist in the Building, and the Tenant gives the
Landlord notice to this effect promptly following the identification of symptoms
of such ailments or illness, then the Landlord shall promptly engage an
environmental consultant selected by Landlord and reasonably satisfactory to the
Tenant (the "Environmental Consultant"), to conduct such investigations and
tests as the Environmental Consultant determines are necessary to ascertain
whether there are environmental conditions existing in the Building that are the
cause of such ailments or illness, and if so, their identity and any appropriate
remedial measures. The landlord and the Tenant shall cooperate with one another
to ascertain the cause of any such ailments or illness, and the symptoms and
duration thereof, and make available to the other such information as may
reasonably be requested. Without limitation, the Tenant shall cause any
information revealed by physical examinations of the occupants of the Premises
suffering from such ailments or illness to be available for review by the
Landlord's occupational health consultant. The Landlord shall use best efforts
to cause a report summarizing the results of the Environmental Consultant's
investigations and tests to be issued within 60 days, but not more than 120 days
of the Tenant's notice as aforesaid and, if a follow-up report is necessary due
to the need for further testing or other contingencies, such follow-up reports
shall be issued as promptly as reasonably possible thereafter (collectively, the
"Report"). The Report shall be furnished to both the Landlord and the Tenant.
The Landlord and the Tenant shall, promptly following the issuance of the
Report, commence the performance of such appropriate remedial measures as are
recommended by the Environmental Consultant in the Report for which they are
respectively responsible under this Lease, and continue to diligently perform
the same, until such measures have been completed.


                                   ARTICLE VI

                                TENANT COVENANTS

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

Section 6.1 - Permitted Uses.

         The Tenant shall occupy the Premises only for the Permitted Uses, and
shall not injure or deface the Premises or the Property, nor permit in the
Premises any auction sale. The Tenant shall give written notice to the Landlord
of any materials on OSHA's right to know list or which are subject to regulation
by any other federal, state, municipal or other governmental authority and which
the Tenant intends to have present at the Premises. The Tenant shall comply with
all requirements of public authorities and of the Board of Fire Underwriters in
connection with methods of storage, use and disposal thereof. The Tenant shall
not permit in the Premises any nuisance, or the emission from the Premises of
any objectionable noise, odor or vibration, nor use or devote the Premises or
any


                                       13
<PAGE>
part thereof for any purpose which is contrary to law or ordinance or liable to
invalidate or increase premiums for any insurance (unless Tenant agrees to pay
therefore) on the Building or its contents or liable to render necessary any
alteration or addition to the Building, other than work in Work Letter attached
as Exhibit C nor commit or permit any waste in or with respect to the Premises,
nor generate, store or dispose of any oil, toxic substances, hazardous wastes,
or hazardous materials (each a, "Hazardous Material"), or permit the same in or
on the Premises or any parking areas provided for under this Lease unless in
accordance with all statutes, rules, regulations, orders and ordinances. The
Tenant shall not dump, flush or in any way introduce any Hazardous Materials
into septic, sewage or other waste disposal systems serving the Premises or any
parking areas provided for under this Lease. The Tenant will indemnify the
Landlord and its successors and assigns against all claims, loss, cost, and
expenses including attorneys' fees, incurred as a result of any contamination of
the Building or any other portion of University Park with Hazardous Materials by
the Tenant or Tenant's contractors, licensees, invitees, agents, servants or
employees.

Section 6.2 - Laws and Regulations.

         The Tenant shall comply with all federal, state and local laws,
regulations, ordinances, executive orders, Federal guidelines, and similar
requirements in effect from time to time, including, without limitation, City of
Cambridge ordinances with respect to animal experiments and hazardous waste and
any such requirements pertaining to employment opportunity, anti-discrimination
and affirmative action. Tenant shall provide to Landlord evidence satisfactory
to Landlord that Tenant has obtained all permits or licenses that Tenant is
required to obtain for the handling or disposal of hazardous materials, animal
experimentation, and other operations required in the conduct of Tenant's
business, and shall upon ten (10) days prior written notice provide copies of
all such permits without the initial applications relating to confidential
material submitted to Landlord.

Section 6.3 - Rules and Regulations.

         The Tenant shall not obstruct in any manner any portion of the Property
not hereby leased; shall not permit the placing of any signs, curtains, blinds,
shades, awnings, aerials or flagpoles, or the like, visible from outside the
Premises; and shall comply with all reasonable rules and regulations of uniform
application to all occupants of the Building now or hereafter made by the
Landlord, of which the Tenant has been given notice, for the care and use of the
Property and the parking facilities relating thereto. The Landlord shall not be
liable to the Tenant for the failure of other occupants of the Building to
conform to any such rules and regulations unless such breaching interferes with
Tenant's quite enjoyment of the Premises. The Landlord shall provide, at the
Tenant's expense, a Building Standard tenant name sign at the entryway to the
Premises.

Section 6.4 - Safety Compliance.

         The Tenant shall keep the Premises equipped with all safety appliances
required by law or ordinance or any other regulations of any public authority


                                       14
<PAGE>
because of any non-office use made by the Tenant and to procure all licenses and
permits so required because of such use and, if requested by the Landlord, do
any work so required because of such use, it being understood that the foregoing
provisions shall not be construed to broaden in any way the Tenant's Permitted
Uses. Tenant shall conduct such periodic test, evaluations or certifications of
safety appliances and laboratory equipment as are required or recommended in
accordance with generally accepted standards for good laboratory practice to
ensure that such safety appliances and equipment remain in good working order,
and shall provide to Landlord copies of such reports, evaluations and
certifications as they are periodically obtained by Tenant or upon ten (10) days
advance notice from Landlord.

Section 6.5 - Landlord's Entry.

         The Tenant shall permit the Landlord and it agents, after reasonable
notice except in the case of emergencies, to enter the Premises at all
reasonable hours for the purpose of inspecting or of making repairs to the same,
monitoring Tenant's compliance with the requirements and restrictions set forth
in this Lease, and for the purpose of showing the Premises to prospective
purchasers and mortgagees at all reasonable times and to prospective tenants
provided that Landlord believes to have a bonafide interest in leasing the
premises that in connection with such entry, Tenant may provide procedures
reasonably designed so as not to jeopardize Tenant's trade secrets, proprietary
technology or critical business operations.

Section 6.6 - Floor Load.

         The Tenant shall not place a load upon any floor in the Premises
exceeding the floor load per square foot of area which such floor was designed
to carry and which is allowed by law; and not move any safe, vault or other
heavy equipment in, about or out of the Premises except in such manner and at
such time as the Landlord shall in each instance authorize. The Tenant's
machines and mechanical equipment shall be placed and maintained by the Tenant
at the Tenant's expense in settings sufficient to absorb or prevent vibration or
noise that may be transmitted to the Building structure or to any other space in
the Building.

Section 6.7 - Personal Property Tax.

         The Tenant shall pay promptly when due all taxes which may be imposed
upon personal property (including, without limitation, fixtures and equipment)
in the Premises to whomever assessed.

Section 6.8 - Assignment and Subleases.

         The Tenant shall not assign, mortgage, pledge, hypothecate or otherwise
transfer this Lease, or sublet (which term, without limitation, shall include
granting of concessions, licenses and the like) the whole or any part of the
Premises without, in each instance, having first received the consent of the
Landlord which consent shall not be unreasonably withheld. Any assignment or
sublease made without such consent shall be void. The Landlord shall not be
deemed to be unreasonable in withholding its consent to any proposed assignment
or subletting by the Tenant based on any of the following factors:

                                       15
<PAGE>
         (a)      The business of the proposed occupant is not consistent with
                  the image and character which the Landlord reasonably desires
                  to promote for the building.

         (b)      The proposed assignment or subletting could adversely affect
                  the ability of the Landlord and its affiliates to 1ease space
                  in the Building or elsewhere in University Park, including
                  leasing space to any proposed assignee or subtenant.

         Whether or not the Landlord consents to any assignment or subletting,
the Tenant named herein shall remain fully and primarily liable for the
obligations of the tenant hereunder, including, without limitation, the
obligation to pay Annual Fixed Rent and Additional Rent provided under this
Lease.

         The Tenant shall give the Landlord notice of any proposed sublease or
assignment, specifying the provisions of the proposed subletting or assignment,
including (i) the name and address of the proposed subtenant or assignee, (ii) a
copy of the proposed subtenant's or assignee's most recent annual financial
statement, (iii) all of the terms and provisions upon which the proposed
subletting or assignment is to be made and such other information concerning the
proposed subletting or assignment is to be made and such other information
concerning the proposed subtenant or assignee as the Tenant has obtained in
connection with the proposed subletting or assignment. The Tenant shall
reimburse the Landlord promptly for actual legal and other expense incurred by
the Landlord in connection with any request by the Tenant for consent to any
assignment or subletting. If this Lease is assigned, or if the Premises or any
part thereof is sublet or occupied by anyone other than the Tenant, the Landlord
may, at any time and from time to time, collect rent and other charges from the
assignee, sublessee or occupant and apply the net amount collected to the rent
and other charges herein reserved, but no such assignment, subletting, occupancy
or collection shall be deemed a waiver of the prohibitions contained in this
Section 6.8 or the acceptance of the assignee, sublessee or occupant as a
tenant, or a release of the Tenant from the further performance by the Tenant of
covenants on the part of the Tenant herein contained. The Tenant shall pay to
the Landlord any amounts the Tenant receives from any subtenant or assignee as
rent, additional rent or other forms of compensation or reimbursement other than
those which are less than or equal to the then due and payable proportionate
monthly share of Annual Fixed Rent, Additional Rent and all other monies due to
Landlord pursuant to this Lease (allocable in the case of a sublease to that
portion of the Premises being subleased). The consent by the Landlord to an
assignment or subletting shall not be construed to relieve the Tenant from
obtaining the express consent in writing of the Landlord to any further
assignment or subletting.


                                       16
<PAGE>
                                   ARTICLE VII

                             INDEMNITY AND INSURANCE

Section 7.1 - Indemnity.

         To the maximum extent this agreement may be made effective according to
law, the Tenant agrees to indemnify and save harmless the Landlord from and
against all claims, loss, or damage of whatever nature arising from any breach
by Tenant of any obligation of Tenant under this Lease or from any act, omission
or negligence of the Tenant, or the Tenant's contractors, licensees, invitees,
agents, servants or employees, or arising from any accident, injury or damage
whatsoever caused to any person or property, occurring after the date that
possession of the Premises is first delivered to the Tenant and until the end of
the Term and thereafter, so long as the Tenant is in occupancy of any part of
the Premises, in or about the Premises or arising from any accident, injury or
damage occurring outside the Premises but within the Building, on the Land, on
the access roads and ways, in the parking facilities provided pursuant to the
Lease, within University Park or any adjacent area maintained by Landlord or any
individual or entity affiliated with Landlord, where such accident, injury or
damage results, or is claimed to have resulted, from an act or omission on the
part of the Tenant or the Tenant's agents or employees, licensees, invitees,
servants or contractors. Landlord agrees to indemnify and save Tenant harmless
from and against all claims, loss or' damage of whatever nature, including
reasonable attorneys' fees, and excepting punitive and/or consequential damages
arising from any breach by Landlord of any obligations of Landlord hereunder or
from any act, omission or negligence of Landlord or its contractors, licensees,
agents, servants or employees, or from environmental contamination within the
Building that substantially affects Tenant's use of the Premises, other than
contamination for which Tenant is responsible. This indemnity and hold harmless
agreement shall include indemnity against attorneys' fees and all other costs,
expenses and liabilities incurred or in connection with any such claim or
proceeding brought thereon, and the defense thereof.

Section 7.2 - Liability Insurance.

         The Tenant agrees to maintain in full force from the date upon which
the Tenant first enters the Premises for any reason, throughout the Term, and
thereafter, so long as the Tenant is in occupancy of any part of the Premises, a
policy of comprehensive general liability insurance under which the Landlord
(and any individuals or entities affiliated with the Landlord, any ground lessor
and any holder of a mortgage on the Property of whom the Tenant is notified by
the Landlord) and the Tenant are named as insureds, and under which the insurer
provides a contractual liability endorsement insuring against all cost, expense
and liability arising out of or based upon any and all claims, accidents,
injuries and damages described in Section 7.1, in the broadest form of such
coverage from time to time available. Each such policy shall be noncancellable
and nonamendable (to the extent that any proposed amendment reduces the limits
or the scope of the insurance required in this Lease) with respect to the
Landlord and such ground lessors and mortgagees without thirty (30) days' prior
notice to the Landlord and such ground lessors and mortgagees and at the
election of the Landlord, either a certificate or insurance or a duplicate
original policy


                                       17
<PAGE>
shall be delivered to the Landlord. The minimum limits of liability of such
insurance as of the Commencement Date shall be Three Million Dollars
($3,000,000.00) for combined bodily injury (or death) and damage to property
(per occurrence), and from time to time during the Term such limits of liability
shall be increased to reflect such higher limits as are customarily required
pursuant to new leases of space in the Boston-Cambridge area with respect to
similar properties.

Section 7.3 - Personal Property at Risk.

         The Tenant agrees that all of the furnishings, fixtures, equipment,
effects and property of every kind, nature and description of the Tenant and of
all persons claiming by, through or under the Tenant which, during the
continuance of this Lease or any occupancy of the Premises by the Tenant or
anyone claiming under the Tenant which, during the continuance of this Lease or
any occupancy of the Premises by the Tenant or anyone claiming under the Tenant,
may be on the Premises or elsewhere in the Building or on the Lot or parking
facilities provided hereby, shall be at the sole risk and hazard of the Tenant,
and if the whole or any part thereof shall be destroyed or damaged by fire,
water or otherwise, or by the leakage or bursting of water pipes, steam pipes,
or other pipes, by theft or from any other cause, no part of said loss or damage
is to be charged to or be borne by the Landlord, except for gross negligence and
except that the Landlord shall in no event be exonerated from any liability to
the Tenant or to any person, for any injury, loss, damage or liability to the
extent such exoneration is prohibited by law.

Section 7.4 - Landlord's Insurance.

         The Landlord shall carry such casualty and liability insurance upon and
with respect to operations at the Building, as may from time to time be deemed
reasonably prudent by the Landlord or required by any mortgagee holding a
mortgage thereon or any ground lessor of the Land, and in any event, insurance
against loss by fire and the risks now covered by extended coverage endorsement
No. 4 in an amount at least equal to eighty percent (80%) of the replacement
value of the Building, exclusive of foundations, site preparation and other
nonrecurring construction costs.

Section 7.5 - Waiver of Subrogation.

         Any insurance carried by either party with respect to the Building,
Land, Premises, parking facilities or any property therein or occurrences
thereon shall, without further request by either party, if it can be so written
without additional premium, or with an additional premium which the other party
elects to pay, include a clause or endorsement denying to the insurer rights of
subrogation against the other party to the extent rights have been waived by the
insured prior to occurrence of injury or loss. Each party, notwithstanding any
provisions of this Lease to the contrary, hereby waives any rights of recovery
against the other for injury or loss, including, without limitation, injury or
loss caused by negligence of such other party, due to hazards covered by
insurance containing such clause or endorsement to the extent of the
indemnification received thereunder.


                                       18
<PAGE>
                                  ARTICLE VIII

                           CASUALTY AND EMINENT DOMAIN

Section 8.1 - Restoration Following Casualties.

         If, during the Term, the Building or Premises shall be damaged by fire
or casualty, subject to the exceptions and limitations provided below, the
Landlord shall proceed promptly to exercise reasonable efforts to restore the
Building or Premises to substantially the condition thereof at the time of such
damage, but the Landlord shall not be responsible for delay in such restoration
which may result from any cause beyond the reasonable control of the Landlord.
The Landlord shall have no obligation to expend in the reconstruction of the
Building more than the actual amount of the insurance proceeds made available to
the Landlord by its insurer and not retained by the Landlord's mortgagee or
ground lessor. Any restoration of the Building or the Premises shall be altered
to the extent necessary to comply with then current laws and applicable codes.

Section 8.2 - Landlord's Termination Election.

         If the Landlord reasonably determines that the amount of insurance
proceeds available to the Landlord is insufficient to cover the cost of
restoring the Building or if in the reasonable opinion of the Landlord the
Building has been so damaged that it is appropriate for the Landlord to raze or
substantially alter the Building, then the Landlord may terminate this Lease by
giving notice to the Tenant within ninety (90) days after the date of the
casualty or such later date as is required to allow the Landlord a reasonable
time to make either such determination. Any such termination shall be effective
on the date designated in such notice from the Landlord, but in any event, not
later than ninety (90) days after such notice, and if no date is specified,
effective upon the delivery of such notice.

Section 8.3 - Tenant's Termination Election.

         Unless the Landlord has earlier advised the Tenant of the Landlord's
election to terminate this Lease pursuant to Section 8.2, or to restore the
Premises and maintain this Lease in effect pursuant to Section 8.1, the Tenant
shall have the right after the expiration of ninety (90) days after any casualty
which materially impairs a material portion of the Premises to give a written
notice to the Landlord requiring the Landlord within ten (10) days thereafter to
exercise or waive any right of the Landlord to terminate this Lease pursuant to
Section 8.2 as a result of such casualty and if the Landlord fails to give
timely notice to the Tenant waiving any right under Section 8.2 to terminate
this Lease based on such casualty, the Tenant shall be entitled, at any time
until the Landlord has given notice to the Tenant waiving such termination
right, to give notice to the Landlord terminating this Lease. Where the Landlord
is obligated to exercise reasonable efforts to restore the Premises, unless such
restoration is completed within six (6) months from the date of the casualty or
taking, such period to be subject, however, to extension where the delay in
completion of such work is due to External Causes (but in no event beyond nine
(9) months from the date of the casualty or taking), the Tenant shall have the
right to terminate this Lease at any time after the expiration of such one-year
(as extended) period


                                       19
<PAGE>
until the restoration is substantially completed, such termination to take
effect as of the date of the Tenant's notice.

Section 8.4 - Casualty at Expiration of Lease.

         If the Premises shall be damaged by fire or casualty in such a manner
that the Premises cannot, in the ordinary course, reasonably be expected to be
repaired within one hundred and twenty (120) days from the commencement of
repair work and such damage occurs within the last eighteen (18) months of the
Term (as the same may have been extended prior to such fire or casualty), either
party shall have the right, by giving notice to the other not later than sixty
(60) days after such damage, to terminate this Lease, whereupon this Lease shall
terminate as of the date of such notice.

Section 8.5 - Eminent Domain.

         Except as hereinafter provided, if the Premises, or such portion
thereof as to render the balance (if reconstructed to the maximum extent
practicable in the circumstances) unsuitable for the Tenant's purposes, shall be
taken by condemnation or right of eminent domain, the Landlord or the Tenant
shall have the right to terminate this Lease by notice to the other of its
desire to do so, provided that such notice is given not later than thirty (30)
days after the effective date of such taking. If so much of the Building shall
be so taken that the Landlord determines that it would be appropriate to raze or
substantially alter the Building, the Landlord shall have the right to terminate
this Lease by giving notice to the Tenant of the Landlord's desire to do so not
later than thirty (30) days after the effective date of such taking.

         Should any part of the Premises be so taken or condemned during the
Term, and should this Lease be not terminated in accordance with the foregoing
provisions, the Landlord agrees to use reasonable efforts to put what may remain
of the Premises into proper condition for use and occupation as nearly like the
condition of the Premises prior to such taking as shall be practicable, subject,
however, to applicable laws and codes then in existence and to the availability
of sufficient proceeds from the eminent domain taking not retained by any
mortgagee or ground lessor.

Section 8.6 - Rent After Casualty or Taking.

         If the Premises shall be damaged by fire or other casualty, except as
provided below, the Annual Fixed Rent and Additional Rent shall be justly and
equitably abated and reduced according to the nature and extent of the loss of
use thereof suffered by the Tenant. If the fire or other casualty was caused by
the Tenant, such abatement shall be made only to the extent that the Landlord is
fully compensated therefor by any lost rent insurance. In the event of a taking
which permanently reduces the area of the Premises, a just proportion of the
Annual Fixed Rent shall be abated for the remainder of the Term.

Section 8.7 - Temporary Taking.

         In the event of any taking of the Premises or any part thereof for a
temporary use not in excess of six (6) months, (i) this Lease shall be and
remain


                                       20
<PAGE>
unaffected thereby and Annual Fixed Rent and Additional Rent shall not abate,
and (ii) the Tenant shall be entitled to receive for itself such portion or
portions of any award made for such use with respect to the period of the taking
which is within the Term.

Section 8.8 - Taking Award.

         Except as otherwise provided in Section 8.7, the Landlord shall have
and hereby reserves and accepts, and the Tenant hereby grants and assigns to the
Landlord, all rights to recover for damages to the Building and the Land, and
the leasehold interest hereby created, and to compensation accrued or hereafter
to accrue by reason of such taking, damage or destruction, as aforesaid, and by
way of confirming the foregoing, the Tenant hereby grants and assigns to the
Landlord, all rights to such damages or compensation. Nothing contained herein
shall be construed to prevent the Tenant from prosecuting in any condemnation
proceedings a claim for relocation expenses, provided that such action shall not
affect the amount of compensation otherwise recoverable by the Landlord from the
taking authority pursuant to the preceding sentence.

                                   ARTICLE IX

                                     DEFAULT

Section 9.1 - Tenant's Default.

         Each of the following shall constitute an Event of Default:

         (a)      Failure on the part of the Tenant to pay the Annual Fixed
                  Rent, Additional Rent or other charges for which provision is
                  made herein on or before the date on which the same become due
                  and payable, if such condition continues for five (5) days
                  after notice that the same are due.

         (b)      Failure on the part of the Tenant to perform or observe any
                  other term or condition contained in this Lease if the Tenant
                  shall not cure such failure within thirty (30) days after
                  notice from the Landlord to the Tenant thereof, provided that
                  in the case of breaches of obligations under this Lease which
                  are susceptible to cure but cannot be cured within thirty (30)
                  days through the exercise of due diligence, so long as the
                  Tenant commences such cure within thirty (30) days, such
                  breach remains susceptible to cure, and the Tenant diligently
                  pursues such cure, such beach shall not be deemed to create an
                  Event of Default.

         (c)      The taking of the estate hereby created on execution or by
                  other process of law; or a judicial declaration that the
                  Tenant is bankrupt or insolvent according to law; or any
                  assignment of the property of the Tenant for the benefit of
                  creditors; or the appointment of a receiver, guardian,
                  conservator, trustee in bankruptcy or other similar officer to
                  take charge of all or any substantial part of the Tenant's
                  property by a court of competent


                                       21
<PAGE>
                  jurisdiction; or the filing of an involuntary petition against
                  the Tenant under any provisions of the bankruptcy act now or
                  hereafter enacted if the same is not dismissed within ninety
                  (90) days; the filing by the Tenant of any voluntary petition
                  for relief under provisions of any bankruptcy law now or
                  hereafter enacted.

         If an Event of Default shall occur, then, in any such case, whether or
not the Term shall have begun, the Landlord lawfully may, immediately or at any
time thereafter, give notice to the Tenant specifying the Event of Default and
this Lease shall come to an end on the date specified therein as fully and
completely as if such date were the date herein originally fixed for the
expiration of the Lease Term, and the Tenant will then quit and surrender the
Premises to the Landlord, but the Tenant shall remain liable as hereinafter
provided.

Section 9.2 - Damages.

         In the event that this Lease is terminated, the Tenant covenants to pay
to the Landlord forthwith on the Landlord's demand, as compensation, an amount
(the Lump Sum Payment) equal to the excess, if any, of the discounted present
value of the total rent reserved for the remainder of the Term over the then
discounted present fair rental value of the Premises for the remainder of the
Term. In calculating the rent reserved, there shall be included, in addition to
the Annual Fixed Rent and all Additional Rent, the value of all other
considerations agreed to be paid or performed by the Tenant over the remainder
of the Term. In addition, the Tenant shall pay punctually to the Landlord all
the sums (Periodic Payments) and perform all the obligations which the Tenant
covenants in this Lease to pay and to perform in the same manner and to the same
extent and at the same time as if this Lease had not been terminated. In
calculating the amounts to be paid by the Tenant under the foregoing covenant,
the Tenant shall be credited with the net proceeds of any rent obtained by
reletting the Premises, after deducting all the Landlord's expenses in
connection with such reletting, including, without limitation, all repossession
costs, brokerage commissions, fees for legal services and expenses of preparing
the Premises for such reletting. The Tenant shall also be entitled to credit
against the last periodic payments which would otherwise become due the amount,
if any, paid to the Landlord as a Lump Sum Payment. The Landlord may (i) relet
the Premises, or any part or parts thereof, for a term or terms which may, at
the Landlord's option, exceed or be equal to or less than the period which would
otherwise have constituted the balance of the Term, and may grant such
concessions and free rent as the Landlord in its reasonable commercial judgment
considers advisable or necessary to relet the same and (ii) make such
alterations, repairs and improvements in the Premises as the Landlord in its
reasonable commercial judgment considers advisable or necessary to relet the
same. No action of the Landlord in accordance with foregoing or failure to relet
or to collect rent under reletting shall operate to release or reduce the
Tenant's liability. The Landlord shall be entitled to seek to rent other
properties of the Landlord prior to reletting the Premises.

Section 9.3 - Cumulative Rights.

         The specific remedies to which the Landlord may resort under the terms
of this Lease are cumulative and are not intended to be exclusive of any other


                                       22
<PAGE>
remedies or means of redress to which it may be lawfully entitled in case of any
breach or threatened breach by the Tenant of any provisions of this Lease. In
addition to the other remedies provided in this Lease, the Landlord shall be
entitled to the restraint by injunction of the violation or attempted or
threatened violation of any of the covenants, conditions or provisions of this
Lease or to a decree compelling specific performance of any such covenants,
conditions or provisions. Nothing contained in this Lease shall limit or
prejudice the right of the Landlord to prove for and obtain in proceedings for
bankruptcy, insolvency or like proceedings by reason of the termination of this
Lease, an amount equal to the maximum allowed by any statute or rule of law in
effect at the time when, and governing the proceedings in which, the damages are
to be proved, whether or not the amount be greater, equal to, or less than the
amount of the loss or damages referred to above.

Section 9.4 - Landlord's Self-help.

         If the Tenant shall at any time default in the performance of any
obligation under this Lease, the Landlord shall have the right, but not the
obligation, upon reasonable, but in no event more than ten (10) days' notice to
the Tenant (except in case of emergency in which case no notice need be given),
to perform such obligation. The Landlord may exercise its rights under this
Section without waiving any other of its rights or releasing the Tenant from any
of its obligations under this Lease.

Section 9.5 - Enforcement Expenses.

         The Tenant shall promptly reimburse the Landlord for all costs and
expenses, including without limitation legal fees, incurred by the Landlord in
exercising and enforcing its rights under this Lease following the Tenant's
failure to comply with its obligations hereunder, whether or not such failure
constitutes an Event of Default on the part of the Tenant, together with
interest at the applicable rate specified in Section 9.6 from the date paid by
the Landlord.

Section 9.6 - Late Charges and Interest on Overdue Payments.

         In the event that any payment of Annual Fixed Rent or Additional Rent
shall remain unpaid for a period of five (5) business days following notice by
the Landlord to the Tenant that such payment is overdue, there shall become due
to the Landlord from the Tenant, as Additional Rent and as compensation for the
Landlord's extra administrative costs in investigating the circumstances of late
rent, a late charge of three percent (3%) of the amount overdue. In addition,
any Annual Fixed Rent and Additional Rent not paid when due shall bear interest
from the date due to the Landlord until paid at the variable rate (the "Default
Interest Rate") equal to the higher of (i) the rate at which interest accrues on
amounts not paid when due under the terms of the Landlord's financing for the
Building, as from time to time in effect, and (ii) one hundred and twenty-five
percent (125%) of the rate from time to time announced by The First National
Bank of Boston as its base rate, or if such rate can no longer be determined,
one hundred and twenty-five percent (125%) of the rate from time to time
announced by a major commercial bank selected by the Landlord as the rate
charged to creditworthy commercial clients for short-term unsecured borrowings.


                                       23
<PAGE>
Section 9.7 - Landlord's Right to Notice and Cure.

         The Landlord shall in no event be in default in the performance of any
of the Landlord's obligations hereunder unless and until the Landlord shall have
failed to perform such obligations within thirty (30) days, or such additional
time as is reasonably required to correct any such default, after notice by the
Tenant to the Landlord expressly specifying wherein the Landlord has failed to
perform any such obligation.

                                    ARTICLE X

                     MORTGAGEES' AND GROUND LESSORS' RIGHTS

Section 10.1 - Subordination.

         This Lease shall, at the election of the holder of any mortgage or
ground lease on the Property, be subject and subordinate to any and all
mortgages or ground leases on the Property, so that the lien of any such
mortgage or ground lease shall be superior to all rights hereby or hereafter
vested in the Tenant.

Section 10.2 - Prepayment of Rent not to Bind Mortgagee.

         No Annual Fixed Rent, Additional Rent, or any other charge payable to
the Landlord shall be paid more than thirty (30) days prior to the due date
thereof under the terms of this Lease and payments made in violation of this
provision shall (except to the extent that such payments are actually received
by a mortgagee or ground lessor) be a nullity as against such mortgagee or
ground lessor and the Tenant shall be liable for the amount of such payments to
such mortgagee or ground lessor.

Section 10.3 - Tenant's Duty to Notify Mortgagee: Mortgagee's Ability to Cure.

         No act or failure to act on the part of the Landlord which would
entitle the Tenant under the terms of this Lease, or by law, to be relieved of
the Tenant's obligations to pay Annual Fixed Rent or Additional Rent hereunder
or to terminate this Lease, shall result in a release or termination of such
obligations of the Tenants or a termination of this Lease unless (i) the Tenant
shall have first given written notice of the Landlord's act or failure to act to
the Landlord's mortgagees or ground lessors of record, if any, of whose identity
and address the Tenant shall have been given actual notice, specifying the act
or failure to act on the part of the Landlord which would give basis to the
Tenant's rights; and (ii) such mortgagees or ground lessors, after receipt of
such notice, have failed or refused to correct or cure the condition complained
of within a reasonable time thereafter, which shall include a reasonable time
for such mortgagee or ground lessors, to obtain possession of the Property if
possession is necessary for the mortgagee or ground lessor to correct or cure
the condition and if the mortgagee or ground lessor notifies the Tenant of its
intention to take possession of the Property and correct or cure such condition.


                                       24
<PAGE>
Section 10.4 - Estoppel Certificates.

         Each party hereto shall from time to time, upon not less than fifteen
(15) days' prior written request by the other party, execute, acknowledge and
deliver to the other party a statement in writing certifying to the Landlord or
an independent third party, with a true and correct copy of this Lease attached
thereto, (i) that this Lease is unmodified and in full force and effect (or, if
there have been any modifications, that the same is in full force and effect as
modified and stating the modifications); (ii) that such person has no knowledge
of any defenses, offsets or counterclaims against its obligations to pay the
Annual Fixed Rent and Additional Rent and to perform its other covenants under
this Lease (or if there are any defenses, offsets, or counterclaims, setting
them forth in reasonable detail); (iii) that there are no known uncured defaults
of the Landlord or the Tenant under this Lease (or if there are known defaults,
setting them forth in reasonable detail); (iv) the dates to which the Annual
Fixed Rent, Additional Rent and other charges have been paid; (v) that the
Tenant has accepted, is satisfied with, and is in full possession of the
Premises, including all improvements, additions, and alterations thereto
required to be made by Landlord under the Lease; (vi) that the Landlord has
satisfactorily complied with all of the requirements and conditions precedent to
the commencement of the Term of the Lease as specified in the Lease; (vii) the
Term, the Commencement Date, and any other relevant dates, and that the Tenant
has been in occupancy since the Commencement Date and paying rent since the
specified dates; (viii) that no monetary or other considerations, including, but
not limited to, rental concessions for Landlord, special tenant improvements or
Landlord's assumption of prior lease obligations of Tenant have been granted to
Tenant by Landlord for entering into Lease, except as specified; (ix) that
Tenant has no notice of a prior assignment, hypothecation, or pledge of rents or
of the Lease; (x) that the Lease represents the entire agreement between
Landlord and Tenant; (xi) that no prepayment or reduction of rent and no
modification, termination or acceptance of Lease will be valid as to the party
to whom such certificate is addressed without the consent of such party; (xii)
that any notice to Tenant may be given it by certified or registered mail,
return receipt requested, or delivered, at the Premises, or at another address
specified; and (xiii) such other matters with respect to the Tenant and this
Lease as the Landlord may reasonably request. On the Commencement Date, the
Tenant shall, at the request of the Landlord, promptly execute, acknowledge and
deliver to the Landlord a statement in writing that the Commencement Date has
occurred, that the Annual Fixed Rent has begun to accrue and that the Tenant has
taken occupancy of the Premises. Any statement delivered pursuant to this
Section may be relied upon by any prospective purchaser, mortgagee or ground
lessor of the Premises and shall be binding on the Tenant.


                                       25
<PAGE>
                                   ARTICLE XI

                                  MISCELLANEOUS

Section 11.1 - Notice of Lease.

         The Tenant agrees not to record this Lease, but upon request of either
party, both parties shall execute and deliver a memorandum of this Lease in form
appropriate for recording or registration, an instrument acknowledging the
Commencement Date of the Term, and if this Lease is terminated before the Term
expires, an instrument in such form acknowledging the date of termination.

Section 11.2 - Notices.

         Whenever any notice, approval, consent, request, election, offer or
acceptance is given or made pursuant to this Lease, it shall be in writing.
Communications and payments shall be addressed, if to the Landlord, at the
Landlord's Address for Notices as set forth in Exhibit A or at such other
address as may have been specified by prior notice to the Tenant; and if to the
Tenant, at the Tenant's Original Address or at such other place as may have been
specified by prior notice to the Landlord. Any communication so addressed shall
be deemed duly given on the earlier of (i) the date received or (ii) on the
third business day following the day of mailing if mailed by registered or
certified mail, return receipt requested. If the Landlord by notice to the
Tenant at any time designates some other person to receive payments or notices,
all payments or notices thereafter by the Tenant shall be paid or given to the
agent designated until notice to the contrary is received by the Tenant from the
Landlord.

Section 11.3 - Successors and Limitation on Liability on the Landlord.

         The obligations of this Lease shall run with the land, and this Lease
shall be binding upon and inure to the benefit of the parties hereto and their
respective successors and assigns, except that the original Landlord named
herein and each successor Landlord shall be liable only for obligations accruing
during the period of its ownership. The obligations of the Landlord shall be
binding upon the assets of the Landlord consisting of an equity ownership of the
Property but not upon other assets of the Landlord and neither the Tenant, nor
anyone claiming by, under or through the Tenant, shall be entitled to obtain any
judgment creating personal liability on the part of the Landlord or enforcing
any obligations of the Landlord against any assets of the Landlord other than an
equity ownership of the Property.

Section 11.4 - Waivers by the Landlord.

         The failure of the Landlord or the Tenant to seek redress for violation
of, or to insist upon strict performance of, any covenant or condition of this
Lease, shall not be deemed a waiver of such violation nor 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 the Landlord of Annual
Fixed Rent or Additional Rent with knowledge of the breach of any covenant of
this Lease shall not be deemed a waiver of such breach. No provision of this
Lease


                                       26
<PAGE>
shall be deemed to have been waived by the Landlord, unless such waiver be in
writing signed by the Landlord. No consent or waiver, express or implied, by the
Landlord to or of any breach of any agreement or duty shall be construed as a
waiver or consent to or of any other breach of the same or any other agreement
or duty.

Section 11.5 -- Acceptance of Partial Payments of Rent.

         No acceptance by the Landlord of a lesser sum than the Annual Fixed
Rent and Additional Rent then due shall be deemed to be other than a partial
installment of such rent due, 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 the Landlord may accept such check or payment
without prejudice to the Landlord's right to recover the balance of such
installment or pursue any other remedy in this Lease provided. The delivery of
keys to any employee of the Landlord or to the Landlord's agent or any employee
thereof shall not operate as a termination of this Lease or a surrender of the
Premises.

Section 11.6 -- Interpretation and Partial Invalidity.

         If any term of this Lease, or the application thereof to any person or
circumstances, shall to any extent be invalid or unenforceable, the remainder of
this Lease, or the application of such term to persons or circumstances other
than those as to which it is invalid or unenforceable, shall not be affected
thereby, and each term of this Lease shall be valid and enforceable to the
fullest extent permitted by law. The titles of the Articles are for convenience
only and not to be considered in construing this Lease. This Lease contains all
of the agreements of the parties with respect to the subject matter thereof and
supersedes all prior dealings between them with respect to such subject matter.

Section 11.7 -- Quiet Enjoyment.

         So long as the Tenant is not in default under this Lease and observes
all conditions hereof, the Tenant shall peaceably and quietly have, hold and
enjoy the Premises free of any claims by, through or under the Landlord.

Section 11.8 -- Brokerage.

         Landlord and Tenant represents and warrants that they have had no
dealings with any broker or agent other than Meredith & Grew, Incorporated and
Spaulding and Slye in connection with this Lease and each party shall indemnify
and hold harmless the other party from claims for any brokerage commission by
Meredith & Grew, Incorporated and Spaulding and Slye arising out of such
parties' actions. Landlord and Tenant shall hold each other harmless from any
other claims for brokerage fees arising from this Lease.

Section 11.9 -- Surrender of Premises and Holding Over.

         The Tenant shall surrender possession of the Premises on the last day
of the Term and the Tenant waives the right to any notice of termination or
notice to quit. The Tenant covenants that upon the expiration or sooner
termination of this Lease, it shall, without notice, deliver up and surrender
possession of the


                                       27
<PAGE>
Premises in the same condition in which the Tenant has agreed to keep the same
during the continuance of this Lease and in accordance with the terms hereof,
normal wear and tear excepted, first removing therefrom all goods and effects of
the Tenant and any leasehold improvements Landlord specified for removal
pursuant to Section 4.2, and repairing all damage caused by such removal. Upon
the expiration of this Lease or if the Premises should be abandoned by the
Tenant, or this Lease should terminate for any cause, and at the time of such
expiration, vacation, abandonment or termination, the Tenant or Tenant's agents,
subtenants or any other person should leave any property of any kind or
character on or in the Premises, the fact of such leaving of property on or in
the Premises shall be conclusive evidence of intent by the Tenant, and
individuals and entities deriving their rights through the Tenant, to abandon
such property so left in or upon the Premises, and such leaving shall constitute
abandonment of the property. Landlord shall have the right and authority without
notice to the Tenant or anyone else, to remove and destroy, or to sell or
authorize disposal of such property, or any part thereof, without being in any
way liable to the Tenant therefor and the proceeds thereof shall belong to the
Landlord as compensation for the removal and disposition of such property.

         If the Tenant fails to surrender possession of the Premises upon the
expiration or sooner termination of this Lease, the Tenant shall pay to
Landlord, as rent for any period after the expiration or sooner termination of
this Lease an amount equal to twice the Annual Fixed Rent and the Additional
Rent required to be paid under this Lease as applied to any period in which the
Tenant shall remain in possession. Acceptance by the Landlord of such payments
shall not constitute a consent to a holdover hereunder or result in a renewal or
extension of the Tenant's rights of occupancy. Such payments shall be in
addition to and shall not affect or limit the Landlord's right of re-entry,
Landlord's right to collect such damages as may be available at law, or any
other rights of the Landlord under this Lease or as provided by law.

Section 11.10 - Ground Lease.

         This Lease is in all respects subject to the ground lease (the "Ground
Lease") between the Landlord as lessee and Massachusetts Institute of Technology
("MIT") as lessor dated as of August 20, 1986. If the Ground Lease shall
terminate during the Term for any reason whatsoever, except as may otherwise be
agreed between M.I.T. and the Tenant, this Lease shall terminate with the same
force and effect as if such termination date had been named herein as the date
of expiration hereof and if any provision of the Ground Lease shall be
inconsistent with the provisions of this Lease, the provisions of the Ground
Lease shall be deemed to limit the provisions hereof, except as are expressly
otherwise provided in a written agreement signed by MIT, the Landlord and the
Tenant.

Section 11.11 - Security Deposit.

         Tenant has paid to Landlord herewith a security deposit of two (2)
month of the Annual Fixed Rent. Landlord may commingle such deposit with its
other funds and may apply such deposit upon default of Tenant hereunder.
Provided Tenant is not then in default hereunder, Landlord shall return the then
remaining portion of the security deposit to Tenant within thirty (30) days
after the


                                       28
<PAGE>
expiration of this Lease. In the event Landlord applies any such funds, Tenant
shall pay to Landlord as additional rent within ten (10) days after invoice
therefor, the amount of the security deposit applied by Landlord, such that the
balance of the security deposit shall be restored to its original amount.

Section 11.12 - Financial Reporting.

         Tenant shall from time to time (but at least annually) on the
anniversary of the Lease provide Landlord with financial statements of Tenant,
together with related statements of Tenant's operations for Tenant's most recent
fiscal year then ended, certified to Landlord by an independent certified public
accounting firm.

Section 11.13 - Cambridge Employment Plan.

         The Tenant agrees to sign an agreement with the Employment and Training
Agency designated by the City Manager of the City of Cambridge as provided in
subsections (a)-(g) of Section 24-4 of Ordinance Number 1005 of the City of
Cambridge, adopted April 23, 1984.

                                             Forest City 38 Sidney Street, Inc.



                                             By: /s/ Gayle Friedland
                                                 -----------------------------


                                             Tenant:

                                             Acusphere, Inc.



                                             By: /s/ Sherri C. Oberg
                                                 -----------------------------
                                                 President and CEO


                                       29
<PAGE>
STATE OF                   )
                           )     SS:
COUNTY OF                  )

         BEFORE ME, a Notary Public in and for said County and State, personally
appeared the above named Forest City 38 Sidney Street, Inc., by _______________,
its ________________________, who acknowledged that he did sign the foregoing
instrument and that the same is his free act and deed and the free act and deed
of said corporation.

         IN TESTIMONY WHEREOF, I have hereunto set my hand and official seal at

____________________________, this _____ day of ___________________, 19__.



                                             ___________________________________
                                             Notary Public


STATE OF                   )
                           )     SS:
COUNTY OF                  )

         BEFORE ME, a Notary Public in and for said County and State, personally
appeared the above named Acusphere, Inc., by __________________________________,
its ______________________________, who acknowledged that he did sign the
foregoing instrument and that the same is his free act and deed and the free act
and deed of said corporation.

         IN TESTIMONY WHEREOF, I have hereunto set my hand and official seal at

____________________________, this _____ day of ___________________, 19__.



                                             ___________________________________
                                             Notary Public


                                       30
<PAGE>
This Instrument Prepared By:
Lawrence R. Fishman, Esq.
10800 Brookpark Road
Cleveland, Ohio 44130
(216) 267-1200



                                       31
<PAGE>
                                    EXHIBIT A

                                Basic Lease Terms


Annual Fixed Rent
for the Initial Term:                   $24.00 per rentable square foot

Security Deposit:                       A sum equal to two months' rent, payable
                                        upon Lease execution.

Initial Term:                           Eighteen (18) months commencing on the
                                        Commencement Date as defined in Section
                                        2.5 of the Lease.

Extension Option:                       Tenant shall have one (1) option to
                                        extend the term of the Lease for an
                                        additional eighteen (18) months on the
                                        same terms and conditions except rent
                                        shall be increased by the CPI percentage
                                        change for such period, but rent shall
                                        not be less than the prior period.

Landlord's Original Address:            Forest City 38 Sidney Street, Inc.
                                        10800 Brookpark Road
                                        Cleveland, Ohio 44130
                                        Attention: James Ratner, President

Landlord's Address for Notices:         Landlord's Original Address with a copy
                                        to:

                                        Forest City 38 Sidney Street, Inc.
                                        64 Sidney Street
                                        Cambridge, Massachusetts 02139-4234
                                        Attention: Gayle Friedland, Vice
                                        President

Original Premises:                      Approximately 6,801 rentable square
                                        feet; on the first floor of the
                                        building, as shown on Exhibit "B-1"
                                        which equates to 5.58% of the total
                                        building

                                      (i)
<PAGE>
Parking Privileges:                 During the Initial Term, Landlord shall
                                    provide fourteen parking spaces.

                                    Initially, and so long as the Landlord is
                                    able to provide surface parking without
                                    interfering with the Landlord's plans for
                                    the development and leasing of the adjacent
                                    portions of University Park, Landlord shall
                                    provide surface parking for use by the
                                    Tenant in the adjacent parking area for the
                                    Clark Building lot. If during the Initial
                                    Term, Landlord is no longer able to provide
                                    sufficient parking spaces without
                                    interfering with the development and leasing
                                    of the adjacent portions of University Park,
                                    the Landlord shall provide an equal number
                                    of parking spaces for use of the Tenant in
                                    garages or other surface parking lots within
                                    University Park.

                                    During the Initial Term the Tenant shall pay
                                    the market rate from time to time in affect
                                    for any parking spaces provided by Landlord
                                    in garages or in other surface parking lots
                                    as the case may be. Landlord agrees that the
                                    market rate charged to the Tenant for
                                    parking spaces shall be no greater than
                                    rates charged in comparable circumstances in
                                    comparable buildings.

Permitted Uses:                     General business and administrative
                                    offices, biotechnology research, pilot
                                    scale manufacturing and accessory uses
                                    supporting the foregoing.

Scheduled Commencement Date:        April 15, 1995

Tenant's Original Address:          Acusphere, Inc.
                                    c/o MBRI Innovation Center
                                    One Innovation Drive
                                    Worcester, MA. 01605

Landlord's Lender's                 PNC Bank, N.A.
Name and Address:                   Fifth Avenue & Wood Street
                                    Pittsburgh, PA. 15265

                                      (ii)

<PAGE>
                                    EXHIBIT B

                                Legal Description
                                 University Park
                                38 Sidney Street
                                 Building Parcel
                                  Cambridge, MA

                            Revised January 15, 1988


      A certain parcel of land situated on the northeasterly side of Auburn
Street, the southeasterly side of Binney Street, the southwesterly side of
Franklin Street and the northwesterly side of Blanche Street, in the City of
Cambridge, County of Middlesex, Commonwealth of Massachusetts, bounded and
described as follows:

      Beginning at a concrete bound with a drill hole located at the southerly
corner of the lot at the intersection of the northwesterly line of Blanche
Street and the northeasterly line of Auburn Street thence

N 45(degree)33' 16" E     A distance of one hundred ninety nine and fifty four
                          hundredths (199.54) feet to a point thence

N 43(degree)21' 03" W     A distance of one hundred forty eight and seventeen
                          hundredths (148.17) feet to a point thence

S 48(degree)52' 43" W     A distance of one hundred ninety nine and three
                          hundredths (199.03) feet to a point thence

S 43(degree) 10' 25" E    A distance of one hundred fifty two and seventy seven
                          hundredths (152.77) feet to the concrete bound with a
                          drill hole at the point of beginning.

      The above described parcel of land contains an area of 29.983 square
feet or 0.5663 acres of land, more or less, and consists of registered and
unregistered land and is shown on a plan entitled:  "Plan of Land in
Cambridge (Middlesex Country) Mass.: Scale: 1"=20'; September 2, 1987;
Revised to January 18, 1988; Prepared for Forest City Development; Prepared
by: Briggs Associates, Inc.; 400 Hingham Street, Rockland, MA 02370.
<PAGE>
                                 EXHIBIT B-1



                              [FIRST FLOOR PLAN]



<PAGE>

                                    EXHIBIT C

                                   Work Letter


      1. This letter agreement is entered into as of April 18, 1995 between
Forest City 38 Sidney Street, Inc. (the "Landlord") and Acusphere, Inc. (the
"Tenant") in connection with the lease (the "Lease") of even date between the
Landlord and the Tenant relating to Premises in the Building located at 38
Sidney Street, Cambridge, Massachusetts. Terms used in this Agreement and not
otherwise defined are used with the meanings indicated in the Lease. The term
"Tenant's Final Plans" is defined in Section 4 of this Work Letter.

      2. Landlord's Work. The Landlord shall cause the Premises to be built-out
substantially in accordance with Tenant's Final Plans to be attached hereto as
Exhibit C1, which plans shall include all the improvements referenced in
paragraph 5 hereof, which construction shall be performed in a good and
workmanlike manner. Subject to (Force Majeure), and to delays caused by Tenant,
the Landlord shall use reasonable diligence in the construction of the work to
be undertaken by the Landlord in the Premises, so as to complete such work on or
before the Scheduled Commencement Date. Tenant shall not be permitted to occupy
any part of the Premises until Landlord has received written confirmation of
completion from the Building Inspector of the City of Cambridge, as set forth
below.

      3. Substantial Completion. The Premises shall be treated as having been
completed and shall be deemed ready for the Tenant's occupancy on the date on
which Landlord has received confirmation that the Premises may be occupied from
the Building Inspector of the City of Cambridge.

      4. Tenant's Final Plans. The Tenant has approved a detailed floor plan
layout together with construction drawings and written specifications reflecting
the partitions and other improvements desired by Tenant in the Premises
("Tenant's Final Plans"). Landlord shall pay the cost of Tenant's Final Plans.
Construction representatives of the Landlord and the Tenant shall meet at such
times or intervals as either the Landlord or the Tenant may reasonably require
in order to review the progress of construction, exchange information, and
coordinate construction of the work contemplated by the Tenant's Final Plans,
and resolve matters at issue pursuant thereto. Landlord's Construction
Representative is Frank LaPlante. Tenant's Construction Representative is
Howard Bernstein.

      5.    Landlord's Allowance. Landlord shall be responsible for bearing
the following costs:

            (a) completion of all necessary work to install a new tenant entry
package, reception area, remodeled kitchen and new conference room, in
accordance with the Preliminary Plan attached hereto as Exhibit C-la, and for
recarpeting and repainting the Premises, all in accordance with Building
Standard finishes; and

                                      (i)
<PAGE>
            (b) any modifications necessary to upgrade the ventilation system
serving the Premises in a manner that will ensure the proper supply of make-up
air to offset the exhaust requirement from the three fume hoods currently
installed in the Premises, and generally to ensure proper ventilation
throughout; and

            (c)   all architectural, mechanical, electrical and plumbing
drawings necessary for the above-referenced work.

            (The aggregate of the foregoing costs being herein referred to as
"Landlord's Contribution").

      Landlord and Tenant acknowledge that there may be costs in excess of
Landlord's Contribution ("Excess Cost") necessary to complete the Premises for
Tenant's occupancy. Tenant agrees to be responsible for bearing any Excess Costs
relating to work required beyond the scope of (a), (b) and (c) above, or for any
changes of scope or quality requested by Tenant after completion of Tenant's
Final Plans. Tenant agrees to pay such Excess Cost within ten (10) days
following receipt of Landlord's billing therefor.

      6. Agreement on Costs and Modification of Plans. In the event Tenant
desires any modifications to Tenant's Final Plans ("Later Modifications"), the
Landlord shall, as soon as practicable thereafter, quote to the Tenant any
Excess Costs and Scheduling (including any change in the Rent Commencement Date)
resulting from said Later Modifications. The Tenant shall, within two (2)
business days following the date of receipt from the Landlord of the Landlord's
revised quotation, give authorization to the Landlord to proceed with the
construction in accordance with the Tenant's Final Plans as modified. Any delays
caused by Tenant shall not extend the Commencement Date or the Rent Commencement
Date.

      The Tenant shall pay to Landlord as Additional Rent for the Excess Costs
of the amount specified in each Landlord Statement on the date Tenant gives
authorization to the Landlord to proceed with construction.

      In the event a change order decreases the cost of any Tenant Extra, which
has been previously paid for by Tenant, Landlord shall reimburse Tenant for the
amount of such overpayment by Tenant after deducting twenty percent (20%) of the
amount of the overpayment for Landlord's and Contractor's overhead expenses.

      7. Delays. Time is of the essence in connection with authorization to the
Landlord to proceed with construction. The Rent Commencement Date shall not be
extended for any delays caused by Tenant, which may include, but shall not be
limited to, delays attributable to any modification requested by Tenant to
Tenant's Final Plans. Only delays attributable to Landlord may extend the Rent
Commencement Date. If Landlord causes the delay, the Rent Commencement Date
shall be delayed one (1) day for each day of Landlord caused delay. Nothing
contained herein shall limit or qualify or prejudice any other of the covenants,
agreements, terms, provisions and conditions contained in the Lease or in this
Agreement.
                                      (ii)
<PAGE>
      8. Defects in Construction. Without cost to the Tenant, the Landlord shall
correct, either through repair or replacement, any defective workmanship and
materials in the Landlord's work in the Premises undertaken pursuant to this
Work Letter ("Landlord's Work"), latent defects in other improvements, which
shall include environmental conditions not caused by Tenant (together with
Landlord's Work, the "Improvements") provided, as to Landlord's Work, the Tenant
gives the Landlord specific written notice of such defective workmanship or
material, which notice shall be given not later than the expiration of thirty
(30) days following Tenant's occupancy of the Premises, except in the case of
latent defects, as to the Improvements, not caused by Tenant to which the Tenant
shall have notified Landlord, in which event such notice shall be given no later
than the expiration of the twelfth (12th) month following the Commencement Date.
Except to the extent to which the Tenant shall have given the Landlord such
notice, the Tenant shall be deemed conclusively to have approved the Landlord's
construction and shall have no claim that the Landlord has failed to perform any
of the Landlord's obligations relating to construction, including, without
limitation, those under this Exhibit C.

      9. Interpretation and Binding Effect. This Agreement shall be governed by
and construed in accordance with the laws of The Commonwealth of Massachusetts
and shall be binding upon and inure to the respective successors and assigns of
Landlord and Tenant as landlord and tenant respectively under the Lease.

                                          FOREST CITY 38 SIDNEY STREET, INC.


                                          By: /s/ Gayle Friedland
                                             -------------------------

                                          Its: Vice President
                                             -------------------------


                                          ACUSPHERE, INC.


                                          By: /s/ Sherri C. Oberg
                                             -------------------------

                                          Its: President and CEO
                                              -------------------------

                                     (iii)
<PAGE>


                                    EXHIBIT D

                                STANDARD SERVICES



The building standard services shall be defined by the Landlord and its
Management Agent. A listing of services shall be as promulgated from time to
time by the Landlord and shall be further described in the Tenant Handbook.

The following services are provided by the Landlord:

      A.    Regular maintenance of interior, exterior and parking lot
            landscaping.

      B.    Regular maintenance, sweeping and snow removal of building
            exterior areas such as roadways, driveways, sidewalks, parking
            areas and courtyard paving.

      C.    Complete interior and exterior cleaning of all windows three
            times per year.

      D.    Daily, weekday maintenance of hallways, passenger elevators,
            common area bathrooms, lobby areas and vestibules.

      E.    Periodic cleaning of stairwells, freight elevators, and back of
            house areas.

      F.    Daily, weekday rubbish removal of all tenant trash receptacles
            and ash trays.

      G.    Daily, weekday cleaning of Tenant space to building standard.

      H.    Maintenance and repair of base building surveillance and alarm
            equipment, mechanical, electrical, plumbing and life safety
            systems.

      I.    Building surveillance and alarm system operation and live
            monitoring service to building standard specifications.

      J.    Conditioned water for HVAC purposes shall be provided to the
            Premises from central mechanical equipment during the appropriate
            seasons between the hours of 8:00 a.m. to 6:00 p.m. Monday
            through Friday. In other hours, conditioned water will be made
            available at building standard rates.

      K.    Utilities for all interior common areas and exterior building and
            parking lighting.
<PAGE>
                                    EXHIBIT E

                              RULES AND REGULATIONS

DEFINITIONS

Wherever in these Rules and Regulations the work "Tenant" is used, it shall be
taken to apply to and include the Tenant and his agents, employees, invitees,
licensees, contractors, any subtenants and is to be deemed of such number and
gender as the circumstances require. The word "Premises" is to be taken to
include the space covered by the Lease. The work "Landlord" shall be taken to
include the employees and agents of Landlord. Other capitalized terms used but
not defined herein shall have the meanings set forth in the Lease.

GENERAL USE OF BUILDING

      A.    Space for admitting natural light into any public area or tenanted
            space of the Building shall not be covered or obstructed by Tenant
            except in a manner approved by Landlord.

      B.    Toilets, showers and other like apparatus shall be used only for the
            purpose for which they were constructed. Any and all damage from
            misuse shall be borne by Tenant. These rooms should be locked at all
            times.

      C.    Landlord reserves the right to determine the number of letters
            allowed Lessee on any directory it maintains.

      D.    No sign, advertisement, notice or the like, shall be used in the
            Building by Tenant (other than at its office and then only as
            approved by Landlord in accordance with building standards). If
            Tenant violates the foregoing, Landlord may remove the violation
            without liability and may charge all costs and expenses incurred in
            so doing to Tenant.

      E.    Tenant shall not throw or permit to be thrown anything out of
            windows or doors or down passages or elsewhere in the Building,
            or bring or keep any pets therein, or commit or make any indecent
            or improper acts or noises. In addition, Tenant shall not do or
            permit anything which will obstruct, injure, annoy or interfere
            with other tenants or those having business with them, or affect
            any insurance rate on the Building or violate any provision of
            any insurance policy on the Building.

      F.    Unless expressly permitted by the Landlord in writing:

            (1)   No additional locks or similar devices shall be attached to
                  any door or window and no keys other than those provided by
                  the Landlord shall be made for any door. If more than two keys
                  for one lock are desired by the Tenant, the Landlord may
                  provide the same upon payment by the Tenant. Upon termination

                                      (i)
<PAGE>
                  of this lease or of the Tenant's possession, the Lessee shall
                  surrender all keys to the Premises and shall explain to the
                  Landlord all combination locks on safes, cabinets and vaults.

            (2)   In order to insure proper use and care of the Premises Tenant
                  shall not install any shades, blinds, or awnings or any
                  interior window treatment without consent of Landlord (or as
                  otherwise listed in Schedule A). Blinds must be building
                  standard.

            (3)   All doors to the Premises are to be kept closed at all
                  times except when in actual use for entrance to or exit
                  from such Premises. The Tenant shall be responsible for the
                  locking of doors and the closing of any transoms and
                  windows in and to the Premises. Any damage or loss
                  resulting from violation of this rule shall be paid for by
                  the Tenant.

            (4)   The Tenant shall not install or operate any steam or internal
                  combustion engine, boiler, machinery in or about the Premises,
                  or carry on any mechanical business therein. All equipment of
                  any electrical or mechanical nature shall be placed in
                  settings which absorb and prevent any vibration, noise or
                  annoyance.

      G.    Landlord shall designate the time when and the method whereby
            freight, small office equipment, furniture, safes and other like
            articles may be brought into, moved or removed from the Building or
            Premises, and to designate the location for temporary disposition of
            such items.

      H.    In order to insure proper use and care of the Premises Tenant shall
            not allow anyone other than Landlord's employees or contractors to
            clean the Premises without Landlord's permission.

      I.    The Premises shall not be defaced in any way. No changes in
            electrical fixtures or other appurtenances of said Premises shall
            be made without approval by Landlord.

      J.    For the general welfare of all tenants and the security of the
            Building, Landlord may require all persons entering and/or
            leaving the Building to register with the Building attendant by
            signing his name and writing his destination in the Building, and
            the time of entry and actual or anticipated departure, or other
            procedures deemed necessary by Lessor. Landlord may deny entry
            during such hours to any person who fails to provide satisfactory
            identification.

      K.    No animals, birds, pets, and no bicycles or vehicles of any kind
            shall be brought into or kept in or about said Premises or the lobby
            or halls of the Building. Tenant shall not cause or permit any
            unusual or objectionable odors to be produced upon or emanate from
            said Premises.

                                      (ii)
<PAGE>
      L.    Unless specifically authorized by Landlord, employees or agents of
            Landlord shall not perform for nor be asked by Tenant to perform
            work other than their regularly assigned duties.

      M.    Landlord shall have the right to prohibit any advertising by Tenant
            which, in Landlord's opinion tends to impair the reputation of the
            Building or its desirability as an office and R&D building and, upon
            written notice from Landlord, Tenant shall promptly discontinue such
            advertising.

      N.    Canvassing, soliciting and peddling in the Building is prohibited
            and Tenant shall cooperate to prevent the same from occurring.

      O.    All parking, Building operation, or construction rules and
            regulations which may be established from time to time by Landlord
            on a uniform basis shall be obeyed.

      P.    Tenant shall not place a load on any floor of said Premises
            exceeding one hundred (100) pounds per square foot. Landlord
            reserves the right to prescribe the weight and position of all safes
            and heavy equipment.

      Q.    Tenant shall not install or use any air conditioning or heating
            device or system other than those approved by Landlord.

      R.    Landlord shall have the right to make such other and further
            reasonable rules and regulations as in the judgment of Landlord, may
            from time to time be needful for the safety, appearance, care and
            cleanliness of the Building and for the preservation of good order
            therein. Landlord shall not be responsible to Tenant for any
            violation of rules and regulations by other tenants.

      S.    The access road and loading areas, parking areas, sidewalks,
            entrances, lobbies, halls, walkways, elevators, stairways and other
            common area provided by Landlord shall not be obstructed by Tenant,
            or used by him for other purpose than for ingress and egress.

      T.    In order to insure proper use and care of the Premises Tenant shall
            not install any call boxes or communications systems or wiring of
            any kind without Landlord's permission and direction.

      U.    In order to insure proper use and care of the Premises Tenant
            shall not manufacture any commodity, or prepare or dispense for
            sales any foods or beverages, tobacco, flowers, or other
            commodities or articles without the written consent of Landlord.

      V.    In order to insure use and care of the Premises Tenant shall not
            enter any janitors' closets, mechanical or electrical areas,
            telephone closets, loading areas, roof or Building storage areas
            without the written consent of Landlord.

      W.    In order to insure proper use and care of the Premises Tenant
            shall not place door mats in public corridors without consent of
            Landlord.

                                     (iii)

<PAGE>

                                    EXHIBIT F

                         STANDARD OFFICE R & D BUILDING

                               MEASUREMENT METHOD

                             UNIVERSITY PARK AT MIT

                        CAMBRIDGE, MASSACHUSETTS 02139



Measurement Method of Determining Gross Building Area, Gross Floor Area,
Rentable Area and Usable Area.

GROSS BUILDING AREA

The gross building area for any office/R&D Building shall be all the floor area
within the exterior walls of the building (as measured from the exterior surface
of the exterior wall) and enclosed by a roof including shaft openings and two
story lobby openings in the floor area. In addition, free-standing power plants
or other utility structures, to the extent that they service the building, and
rooftop structures, to the extent that they are fully enclosed rooms, are
included.

GROSS FLOOR AREA

The gross floor area of the building includes all the spaces on the floor to the
inside glass face of the windows carried along the entire wall. The gross floor
area includes shaft openings and lobby openings in the floor area.

RENTABLE AREA

The rentable floor area is based on the New York standard definition BOMA
Experience Exchange Report, 1984, page 4. The following is the definition of
rentable area:

1.    The rentable area for each floor includes everything inside the four walls
      including bathrooms, corridors, service vestibules (if any), janitors
      closet, electric/telephone room, storage rooms (if any), and vertical
      shafts reserved for tenant expansion of ducts, plumbing, etc. as all of
      these service areas and corridors benefit the tenant.

2.    The rentable area for each floor excludes the following:

      a.    elevator shafts and their enclosing walls;
      b.    plumbing and any other shafts serving the base building functions
            and their enclosing walls;
      c.    stairwells and their enclosing walls;
      d.    floors at bottom of shafts; and
      e.    floor area omitted at two-story lobby locations.

                                      (i)
<PAGE>
To the rentable area calculation of on each floor are added the following
additional square foot allocation:

The portion of the first floor (or any other floor if applicable, i.e. if some
new building service were provided like a building shower on an upper floor)
which provide services to the entire building. These service areas are to be
totalled and apportioned equally to all floors in the building. Thus each tenant
on every floor served by these service areas, will pay its prorata share of the
rent for that service area. These service areas include the following:

a.    first floor building lobby corridors unless they are only used by first
      floor tenants, entrance vestibules, and security desk floor area (if
      over and above lobby/corridor areas);

b.    loading dock, loading platform, storage room, transformer room, fire
      pump room, switchgear room, mail room, elevator pumproom, and building
      management office; and

c.    electrical rooms serving the entire building and rooftop utility
      structures to the extent that they are fully enclosed rooms containing
      equipment used by the base building or are available for use by individual
      tenants' equipment.

The following first floor areas shall be excluded from the areas apportioned to
all floors and included solely in the rentable area for the first floor:

a.    tenant usable areas on the first floor including the corridor walls;

b.    restrooms;

c.    telephone and any electrical closet serving the first floor only,
      janitorial closet on the first floor; and

d.    tenant vertical shafts.

USABLE AREA

Usable area is that portion of each floor directly apportioned to tenants for
their use. Currently the second through fifth floors are potentially available
for either single tenant or multi-tenant use. The first floor is available on a
multi-tenant basis only (although one tenant could occupy the entire floor).

The multi-tenant usable areas are defined as the interior face of the window
(see definition gross floor area) to the interior face of the corridor (i.e. the
core side of the corridor). The multi-tenant usable area for each tenant space
includes the entire wall between the tenant space and the corridor and, when
there are multiple tenants, half of any demising walls between tenants on any
one floor.

                                      (ii)
<PAGE>

The core areas represent the balance of floor area on each floor which is
factored into the multi-tenant rentable area calculation and apportioned prorata
to each tenant on that floor. The core is defined to include the service
vestibules, corridors and lobby spaces, the tenant vertical chases, the men and
women's restrooms, the janitor's room and electric/telephone room on each floor.

SINGLE TENANT USABLE AREA DEFINITION

The single tenant usable area on each is defined as the entire floor area from
interior face of the window inclusive of the core areas described above as
exclusive of usable area on a multi-tenant floor. This entire core area is
usable on a single tenant floor because it is for that single tenant's exclusive
use and benefit.

Therefore the rentable area and usable area on a floor are the same. Thus, only
the building services rentable area factor described above is added to the
single tenant usable square footage to determine the rentable area charged to
the whole floor user.

                                     (iii)
<PAGE>

                            FIRST AMENDMENT TO LEASE

      WHEREAS, Forest City 38 Sidney Street. Inc., as landlord ("Forest
City"). and Acusphere. Inc., as tenant ("Tenant"), entered into a Lease dated
as of April 18, 1995 (the "Lease") for the Premises described in the Lease:

      WHEREAS, Thirty-Eight Sidney Street Limited Partnership ("Landlord")
has succeeded to the interests of Forest City in and to the Lease; and

      WHEREAS, Landlord and Tenant desire to amend the Lease.

      NOW, THEREFORE, for valuable consideration, receipt of which is hereby
acknowledged, Landlord and Tenant hereby agree to amend the Lease as follows:

      1.    Section 1.2 is hereby amended to add the following new definition:

            "`Expansion Premises' - See Exhibit A-1."

      2.    Section 2.1 is hereby amended to delete the word "Original" from
the first sentence thereof.

      3.    Section 2.5 is hereby amended to delete it in its entirety and to
substitute therefor the following:

            "Section 2.5 - Commencement Date.

                  `Commencement Date' means (i) with respect to the Original
            Premises, the Original Premises Term Commencement Date (as set forth
            in Exhibit A-1), and (ii) with respect to the Expansion Premises,
            the Expansion Premises Term Commencement Date (as set forth in
            Exhibit A-1).

      4.    Section 2.6 is hereby amended to delete it in its entirety.

      5.    Section 3.1 is hereby amended to delete it in its entirety and to
substitute therefor the following:

            "Section 3.1 - Annual Fixed Rent.

                  "From and after the Original Premises Rent Commencement Date
            (as set forth in Exhibit A-1), the Tenant shall pay, without notice


<PAGE>
            or demand, monthly installments of one-twelfth (1/12th) of the
            Annual Fixed Rent in effect and applicable for the Original Premises
            in advance for each full calendar month of the Term and of the
            corresponding fraction of said one-twelfth (1/12th) for any fraction
            of a calendar month at the beginning or end of the Term. The Annual
            Fixed Rent applicable to the Original Premises during the Initial
            Term shall be as set forth in Exhibit A-1.

                  From and after the Expansion Premises Rent Commencement Date
            (as set forth in Exhibit A-1), the Tenant shall pay without notice
            or demand, monthly installments of one-twelfth (1/12th) of the
            Annual Fixed Rent in effect and applicable to the Expansion Premises
            in advance for each full calendar month of the remainder of the Term
            and of the corresponding fraction of said one-twelfth (1/12th) for
            any fraction of a calendar month at the end of the Term. The Annual
            Fixed Rent applicable to the Expansion Premises during the Initial
            Term shall be as set forth in Exhibit A-1."

      6.    Section 11.11 is hereby amended to delete it in its entirety and to
substitute therefor the following:

            "Section 11.11 - Security Deposit.

                  Tenant has paid to Landlord herewith, in cash, a security
            deposit equal to two (2) months' Annual Fixed Rent for the Original
            Premises and Expansion Premises. Landlord may commingle such cash
            with its other funds. Landlord may apply such security deposit to
            cure any default of Tenant hereunder. Provided Tenant is not then in
            default hereunder. Landlord shall return the then remaining portion
            of the security deposit to Tenant within thirty (30) days after the
            expiration of this Lease. In the event Landlord applies any such
            funds, Tenant shall pay to Landlord as Additional Rent within ten
            (10) days after invoice therefor, the amount of the security deposit
            applied by Landlord such that the balance of the security deposit
            shall be restored to its original amount."

      7.    Exhibits A and B-1 to the Lease are hereby amended to delete them
in their entirety and to substitute therefor Exhibits A-1 and B-2,
respectively, attached hereto and made a part hereof.

      8. Landlord agrees to perform the following work in the Expansion
Premises: (1) install a make-up air system sufficient to provide the necessary
make-up air for the two (2) existing fume hoods in the Expansion Premises, (2)
clean and decontaminate all fume hoods and chip tanks (including replacement of
chips if required), and (3) clean and repaint the Expansion Premises.

      Except as herein amended, the Lease shall remain in full force and
effect.


                                       2
<PAGE>
                                   EXHIBIT A-1

                                Basic Lease Terms

Annual Fixed Rent
for the Initial Term:         (a) Original Premises:

                              Original Premises Commencement Date through
                              October 31, 1996:
                              $24.00 per rentable square foot

                              November 1, 1996 through August 31, 1998:
                              $24.75 per rentable square foot

                              (b) Expansion Premises:

                              September 1, 1996 through August 31, 1998:
                              $26.00 per rentable square foot

Initial Term:                 Commencing on the Original Premises Term
                              Commencement Date and terminating on August 31,
                              1998.

Landlord's Original Address:  Thirty-Eight Sidney Street Limited Partnership
                              10800 Brookpark Road
                              Cleveland, Ohio 44130
                              Attention: James Ratner

Landlord's Address for
Notices:                      Landlord's Original Address with a copy to:

                              Thirty-Eight Sidney Street Limited Partnership
                              38 Sidney Street
                              Cambridge, Massachusetts 02139-4234
                              Attention: Gayle Friedland

                              Forest City Commercial Management
                              64 Sidney Street
                              Cambridge, Massachusetts 02139-4234
                              Attention: Peter Calkins

Original Premises:            6,801 rentable square feet, as more
                              particularly depicted on Exhibit "B-2" attached
                              hereto and incorporated herein.

Expansion Premises:           2,370 rentable square feet, as more
                              particularly depicted on Exhibit "B-2."

                                      (i)
<PAGE>

Parking Privileges:           During the Initial Term, Landlord shall provide
                              fourteen parking spaces, except Landlord shall
                              provide eighteen parking spaces upon the
                              earlier to occur of (i) Tenant's written
                              request for four additional spaces or (ii)
                              January 1, 1997.

                              Initially, and so long as the Landlord is able to
                              provide surface parking without interfering with
                              the Landlord's plans for the development and
                              leasing of the adjacent portions of University
                              Park. Landlord shall provide surface parking for
                              use by the Tenant in the adjacent parking area for
                              the Clark Building lot. If during the Initial
                              Term, Landlord is no longer able to provide
                              sufficient parking spaces without interfering with
                              the development and leasing of the adjacent
                              portions of University Park, the Landlord shall
                              provide an equal number of parking spaces for use
                              of the Tenant in garages or other surface parking
                              lots within University Park.

                              During the Initial Term the Tenant shall pay the
                              market rate from time to time in effect for any
                              parking spaces provided by Landlord in garages or
                              in other surface parking lots as the case may be.
                              Landlord agrees that the market rate charged to
                              the Tenant for parking spaces shall be no greater
                              than rates charged in comparable circumstances in
                              comparable buildings.

Permitted Uses:               General business and administrative offices,
                              biotechnology research, pilot scale
                              manufacturing and accessory uses supporting the
                              foregoing.

Original Premises Term
Commencement Date:            May 4, 1995

Expansion Premises Term
Commencement Date:            September 1, 1996

Original Premises Rent
Commencement Date:            May 4, 1995

Expansion Premises Rent
Commencement Date:            September 1, 1996

                                      (ii)
<PAGE>
Tenant's Address:             Acusphere, Inc.
                              38 Sidney Street
                              Cambridge, Massachusetts 02139-4211

Landlord's Lender's
Name and Address:             PNC Bank, N.A.
                              Fifth Avenue & Wood Street
                              Pittsburgh, Pennsylvania 15265

Total Rentable Floor Area
of the Building:              121,622 rentable square feet.


                                     (iii)
<PAGE>


                                 EXHIBIT B-2




                           [FIRST FLOOR PLAN HERE]




<PAGE>



July 1, 1997


                               THE CLARK BUILDING

                                38 Sidney Street
                            Cambridge, Massachusetts



                                   LANDLORD
                THIRTY-EIGHT SIDNEY STREET LIMITED PARTNERSHIP



                                     TENANT
                               ACUSPHERE, INC.


                       RESTATED SECOND AMENDMENT TO LEASE

<PAGE>
                       RESTATED SECOND AMENDMENT TO LEASE


      This RESTATED SECOND AMENDMENT TO LEASE (the "Second Amendment") is
entered into as of the 30th day of June, 1997 by and between THIRTY-EIGHT SIDNEY
STREET LIMITED PARTNERSHIP ("Landlord") and ACUSPHERE, INC. ("Tenant").
Capitalized terms used and not otherwise defined herein shall have the meanings
ascribed to them in the Lease.

      WHEREAS Landlord's predecessor in interest, Forest City 38 Sidney Street
Inc., ("Forest City") and Tenant entered into a Lease dated as of April 18,
1995, which Lease was amended by a First Amendment to Lease dated as of May 24,
1996 (as amended, the "Lease"), and

      WHEREAS, Forest City's interest under the Lease was assigned to
Landlord as of February 1, 1996, and

      WHEREAS, the Initial Term of the Lease will expire on August 31, 1998,
and

      WHEREAS, Landlord and Tenant now desire to amend the Lease in order to
extend the Term, incorporate additional space into the Premises, and modify the
Annual Fixed Rent;

      NOW, THEREFORE, in consideration of the mutual covenants contained herein,
Landlord and Tenant agree that the Lease is amended as follows:

1.    Section 1.2 is hereby amended to add the following definitions:

      "Second Expansion Premises" means the area on the first floor of the
      Building comprising 1,883 rentable square feet, as more particularly shown
      on Exhibit B-3 attached hereto and made a part hereof.

      "Second Expansion Premises Commencement Date" means July 11, 1997 or, if
      later, the date on which the Second Expansion Premises are delivered to
      Tenant in accordance with Section 4 hereof.

      "Second Expansion Premises Annual Fixed Rent" means $33,894.00, based on
      $18.00 per rentable square foot.

      "Extension Term" means the period between September 1, 1998 and December
      31, 1999.

2. Section 2.1 is hereby amended to add the words "and the Second Expansion
Premises" at the end of the first sentence, and all references in the Lease to
the "Premises" shall also include the Second Expansion Premises. All terms and
conditions of the Lease shall apply to the Second Expansion Premises except as
set forth herein.

3. From and after the Second Expansion Premises Commencement Date, Tenant shall
pay, without notice or demand, in advance on the first day of every calendar
month, one twelfth of the Second Expansion Premises Annual Fixed Rent, and shall
pay as Additional Rent the Tenant's

<PAGE>
Tax Expense Allocable to the Premises, and Operating Expenses allocable to the
Premises, which are allocable to the Second Expansion Premises in the same
manner as set forth in the Original Premises. Fixed Rent and Additional Rent for
any partial months shall be pro-rated accordingly.

4. Landlord shall deliver the Second Expansion Premises in As-Is condition,
vacant and free of any personal property belonging to the prior tenant, and with
clean carpets and any damage caused by the prior tenant's relocation from the
Premises repaired. Tenant shall be responsible for performing or causing to be
performed any modifications that Tenant may require within the Second Expansion
Premises at its own cost and expense, subject to Landlord's approval rights as
set forth in the Lease.

5. Tenant's allocation of parking spaces shall be increased by four (4) spaces
on the Second Expansion Premises Commencement Date.

6.    No additional security deposit shall be required in connection with the
Second Expansion Premises.

7. The Term of the Lease is hereby extended to include the Extension Term. If,
prior to the expiration of the Extension Term, Tenant relocates into larger
premises in any building located within the area known as University Park at
MIT, Tenant may, by giving at least 90 days prior notice to Landlord, terminate
this Lease effective upon the date Tenant vacates the Premises.

8.    The Annual Fixed Rent during the Extension Term shall be as follows:

<TABLE>
<CAPTION>
<S>                                 <C>
      Original Premises:            $27.25 per rentable square foot
      Expansion Premises:           $28.60 per rentable square foot
      Second Expansion Premises:    $18.00 per rentable square foot
</TABLE>

9.    No leasing commissions shall be paid in connection with this Second
Amendment to Lease.

10. The Lease is herein incorporated by reference and shall remain in full force
and effect, except as expressly modified herein. This Restated Second Amendment
to Lease shall supersede any other document entitled Second Amendment to Lease,
including the Second Amendment to Lease dated March 31, 1997 and executed by
Landlord and Tenant, and shall be binding upon and shall inure to the benefit of
Landlord and Tenant and their successors and assigns.

TENANT                                 LANDLORD
------                                 --------
ACUSPHERE, INC.                        THIRTY-EIGHT SIDNEY STREET
                                       LIMITED PARTNERSHIP

                                       By:  Forest City 38 Sidney Street, Inc.

                                       Its:   General Partner

By: /s/ Sherri C. Oberg                By: /s/ Gayle Friedland
   ------------------------               ------------------------

Its: President and CEO                 Its: Vice President
   ------------------------               ------------------------

                                       2
<PAGE>
February 26, 1998 revision

                               THE CLARK BUILDING

                                38 Sidney Street
                            Cambridge, Massachusetts

                                    LANDLORD


                THIRTY-EIGHT SIDNEY STREET LIMITED PARTNERSHIP






                                     TENANT


                               ACUSPHERE, INC.




                            THIRD AMENDMENT TO LEASE


<PAGE>


                            THIRD AMENDMENT TO LEASE

      This THIRD AMENDMENT TO LEASE (the "Third Amendment") is entered into as
of the 10th day of March, 1998 by and between THIRTY-EIGHT SIDNEY STREET LIMITED
PARTNERSHIP, a Delaware limited partnership, ("Landlord") and ACUSPHERE, INC.
("Tenant"). Capitalized terms used and not otherwise defined herein shall have
the meanings ascribed to them in the Lease.

      WHEREAS Landlord's predecessor in interest, Forest City 38 Sidney Street
Inc., ("Forest City") and Tenant entered into a Lease dated as of April 18,
1995, which Lease was amended by a First Amendment to Lease dated as of May 24,
1996, between Landlord and Tenant, the Second Amendment to lease dated March 31,
1997, between Landlord and Tenant, and by a Restated Second Amendment to Lease
dated June 30, 1997, between Landlord and Tenant, (as amended, the "Lease"), all
with respect to premises at 38 Sidney Street, Cambridge, Massachusetts, and

      WHEREAS, Forest City's interest under the Lease was assigned to
Landlord as of February 1, 1996, and

      WHEREAS, the Initial Term of the Lease will expire on December 31,
1999, and

      WHEREAS, Landlord and Tenant now desire to amend the Lease in order to
extend the Term and modify the Annual Fixed Rent;

      NOW, THEREFORE, in consideration of the mutual covenants contained herein,
Landlord and Tenant agree that the Lease is amended as follows:

      1.    Section 1.2 is hereby amended to add the following definitions:

            " Second Extension Term" means the period between January 1, 2000
            and December 31, 2000.

      2.    The Term of the Lease is hereby extended to include the Second
            Extension Term. If, prior to the expiration of the Second Extension
            Term, Tenant relocates into larger premises in any building located
            within the area known as University Park at MIT, Tenant may, by
            giving at least 90 days prior notice to Landlord, terminate this
            Lease effective upon the date Tenant vacates the Premises.

      3.    The Annual Fixed Rent during the Second Extension Term shall be
            as follows:

<TABLE>
<CAPTION>
<S>                           <C>
      Original Premises:      $29.00 per rentable square foot
      Expansion Premises:     $29.00 per rentable square foot
      Second Expansion
      Premises:               $19.00 per rentable square foot
</TABLE>
<PAGE>
      4.    The section of Exhibit A-1, attached to said First Amendment to
            Lease, entitled "Parking Privileges" is hereby amended by deleting
            the word "initial" from each place where it appears."

      5.    No leasing commissions shall be paid in connection with this
            Third Amendment to Lease.

The Lease is herein incorporated by reference and shall remain in full force and
effect, except as expressly modified herein.

TENANT                                   LANDLORD
ACUSPHERE, INC.                          THIRTY-EIGHT SIDNEY STREET
                                         LIMITED PARTNERSHIP

                                         By: Forest City 38 Sidney Street, Inc.
                                             ---------------------------------
                                             an Ohio Corporation

                                         Its:General Partner
                                             ---------------------------------


By: /s/ Sherri C. Oberg                  By: /s/ Gayle Friedland
   ----------------------------              -----------------------------------

Its: President and CEO                   Its: Vice President
    ---------------------------              -----------------------------------


                                       2
<PAGE>
                       ASSIGNMENT AND ASSUMPTION OF LEASE

Acusphere, Inc., a Delaware corporation, having an address of 38 Sidney Street,
Cambridge, MA 02139 ("Assignor"), and The General Hospital Corporation, a
Massachusetts corporation, having an address of 55 Fruit Street, Boston, MA
02114 ("Assignee"), enter into this Assignment and Assumption of Lease (the
"Assignment") as of January 17, 2002.

         WHEREAS, Assignor is the current tenant under that certain Lease dated
April 18, 1995 (the "Lease"), as amended pursuant to the terms of that certain
First Amendment to Lease dated as of May 24, 1996, that certain Restated Second
Amendment to Lease dated as of June 30, 1997, that certain Third Amendment to
Lease dated as of March 10, 1998 and that certain Fourth Amendment to Lease
dated as of November 28, 2000, between Assignor and Thirty-Eight Sidney Street
Limited Partnership (as successor in interest to Forest City 38 Sidney Street,
Inc.), a Delaware limited partnership, having an address of 38 Sidney Street,
Cambridge, Massachusetts 02139 ("Landlord"), a copy of which Lease is attached
hereto and incorporated herein as Exhibit A, and pursuant to which Lease
Assignor is currently leasing certain premises (the "Premises") consisting of
11,054 rentable square feet on the First floor of the building known as The
Clark Building, as more particularly described in the Lease; and

         WHEREAS, as of the date on which Assignor delivers the Premises in the
condition required in Section 3 below, currently expected to be January 31, 2002
(the "Effective Date"), Assignor wishes to assign its right, title, interest and
obligations under the Lease and in the Premises to Assignee and Assignee wishes
to accept such assignment and assume the liabilities, duties and obligations of
Assignor under the Lease, except as otherwise provided below.

         NOW, THEREFORE, in consideration of the foregoing, and for other good
and valuable consideration, the receipt and sufficiency of which Assignor and
Assignee hereby acknowledge, Assignor and Assignee agree as follows:

         1. Assignment and Assumption. As of the Effective Date, except as
otherwise provided herein, Assignor hereby assigns all of its right, title,
interest and obligations under the Lease and in the Premises, excluding any
security deposit being held by Landlord for the benefit of Assignor, to Assignee
and Assignee hereby accepts such assignment and unconditionally assumes and
agrees to pay, discharge and perform all of the terms, covenants, conditions and
obligations of Assignor under the Lease, accruing from and after the Effective
Date and, as of the Effective Date, recognizes Landlord as landlord under the
Lease.

         2. Indemnities. Assignor shall indemnify, defend and hold harmless
Assignee from and against all claims, liabilities, damages, losses, costs and
expenses resulting from a breach or default of the obligations of the tenant
under the Lease arising or occurring before the Effective Date or relating to
Assignor's use and occupancy of the
<PAGE>
Premises before the Effective Date. Assignee shall indemnify, defend and hold
harmless Assignor from and against all claims, liabilities, damages, losses,
costs and expenses resulting from a breach or default of the obligations of the
tenant under the Lease arising or occurring on or after the Effective Date or
relating to Assignee's use or occupancy of the Premises on or after the
Effective Date.

         3. (a) Delivery. On the Effective Date Assignor shall deliver the
Premises to Assignee and Assignee shall accept the Premises in its "as is"
condition on the date of the walk through of the Premises by Assignor and
Assignee on January 2, 2002, maintained from that date until the Effective Date
as required under the Lease, with the work described in Exhibit C completed on
or before the Effective Date, and free of tenants and occupants. Assignor will
provide Assignee with a so-called decommissioning letter with respect to the
Premises, if necessary. Assignor shall complete the Hazardous Materials removal
in accordance with Exhibit B. Assignor shall perform the foregoing obligations
at Assignor's sole cost and expense, and in compliance with all federal state
and local laws, rules, regulations and ordinances, any decommissioning or
decontamination requirements imposed by any licenses or permits maintained by
Assignor in connection with the conduct of its business in the Premises, and the
terms and conditions of the Lease as affected by this Assignment.

         (b) Property. Prior to the Effective Date, Assignor will remove
Assignor's property located in the Premises including, but not limited to,
furniture such as tables and chairs, computers, refrigerators, freezers,
humidity chambers, light chambers, incubators, two laminar flow hoods,
autoclave, dishwasher, chromatography systems (liquid and gas), mixing tanks,
dryboxes, chemicals, gas tanks and coulter counters. At least six (6) chemical
fume hoods will remain at the Premises on the Effective Date. In connection with
the removal of the property listed above, Assignor will perform the work, set
forth on Exhibit C. Assignor and Assignee shall do a final walk through prior to
the Effective Date to verify that the Assignor has complied with its obligations
pursuant to this section and Exhibit C.

         4. Rent Adjustment. If any payments of Annual Fixed Rent, Additional
Rent or other charges due under the Lease relate to a period which includes time
both before and after the Effective Date, any such payment shall be prorated
according to the fractions of the total number of days in such period that
occur, respectively, before and after the Effective Date, unless another method
of allocation is more equitable, in the reasonable opinion of both Assignor and
Assignee, in which case the more equitable method will be used. Assignor shall
pay the prorated portion (or if another method is more equitable, its share
under that method) of any such payment relating to the fractional period before
the Effective Date, and Assignee shall pay the prorated portion (or if another
method is more equitable, its share under that method) of any such payment
relating to the fractional period on and after the Effective Date. If the
Effective Date occurs on a date other than the first day of a calendar month,
Assignor shall pay to Landlord all Annual Fixed Rent, Additional Rent and other
charges due under the Lease for the calendar month in which the Effective Date
occurs, and Assignee shall reimburse Assignor the amount of such monthly payment
attributable on a per diem basis to the


                                       2
<PAGE>
period from the Effective Date to the end of such calendar month. Such amount
shall be due to Assignor from Assignee on the Effective Date.

         Assignor shall be responsible for reimbursing Landlord for any costs
incurred by Landlord in connection with this Assignment, in accordance with the
terms of the Lease.

         5. Security Deposit. Assignor does not hereby assign, and hereby
retains all of its rights and interest in the Security Deposit held by Landlord
under the Lease, and to the extent required under Section 11.11 of the Lease,
Landlord shall pay to Assignor the Security Deposit after the termination of the
Lease as amended. Assignee has no liability to Assignor for the Security
Deposit.

         6. Consent/Condition Precedent. Assignor and Assignee hereby agree that
this Assignment, and the rights and obligations of Assignee and Assignor
hereunder, are subject to the condition precedent that Landlord consent to this
Assignment in writing.

         7. Effective Date/Null and Void. Within fifteen (15) days after the
Effective Date, Assignor and Assignee agree to sign jointly and deliver to each
other and Landlord copies of a letter stating the Effective Date, however,
failure to do so shall not affect the validity of this Assignment. If the
Effective Date has not occurred by February 28, 2002, this Assignment will be
null and void and without force or effect.

         8. Representations. Assignor represents and warrants to Assignee that
as of the date hereof (i) the Lease is in full force and effect and has not been
amended other than as hereinabove noted; (ii) neither Assignor nor, to the
knowledge of Assignor, Landlord, is in default under the Lease; (iii) Assignor
has not encumbered the Lease by any prior transfer, assignment or encumbrance;
and (iv) Assignor has not used any radioactive materials or biological materials
in the Premises; and (v) except with respect to Landlord defaults, that these
representations and warranties will also be true as of the Effective Date.

         9. Authority. Each of Assignor and Assignee warrants that it has the
right and authority to enter into this Assignment, that the person or persons
executing this instrument on its behalf are fully authorized to execute this
Assignment, and that this Assignment is the duly authorized act of such party.

         10. No Other Representations. Assignee acknowledges that Assignor has
made no representations and warranties concerning the Premises, its nature,
condition, usability or fitness for Assignee's purpose, except those herein
contained.

         11. Notice. Notices shall be sent in accordance with the manner
provided in Section 11.2 of the Lease, except that if intended for tenant under
the Lease, to Assignee at the address referenced in the first paragraph of this
Assignment,


                                       3
<PAGE>
With a copy to:   Partners HealthCare System, Inc.
                  55 Fruit Street
                  Boston, MA  02114
                  Attention:  Director of Real Estate Development

With a copy to:   Office of the General Counsel
                  Partners HealthCare System, Inc.
                  50 Staniford Street, Suite 1000
                  Boston, MA 02114

and if intended for Assignor after the Effective Date, at the following address:

                  Acusphere, Inc.
                  500 Arsenal Street
                  Watertown, MA
                  Attn:_President

With a copy to:   Testa, Hurwitz & Thibeault, LLP
                  125 High Street
                  Boston, MA  02110
                  Attn:  Real Estate Department

         12. Brokers. Assignor and Assignee represent and warrant to the other
that it has not dealt with any brokers other than Spaulding & Slye Colliers
International and McCall and Almy (the "Brokers") in connection with the
consummation of this Assignment. Assignor represents and warrants to Assignee
that no payments are due to Spaulding & Slye Colliers International. Assignee
shall be solely responsible for any payments due to McCall and Almy. Assignor
and Assignee each shall indemnify and hold harmless the other against any loss,
damage, claims or liabilities arising out of the failure of its representation,
breach of its warranty or failure to pay set forth in this Section.

         13. Successors and Assigns. This Assignment and the covenants contained
herein shall be binding upon and shall inure to the benefit of Assignor and
Assignee and their respective successors and assigns.

         14. Governing Law. This Assignment shall be governed by and construed
in accordance with the laws of the State in which the Premises is located,
excluding any conflict of laws principles that would cause the application of
laws of any other jurisdiction.

         15. Counterparts. This Assignment may be executed in one or more
counterparts, each of which shall be deemed an original and all such
counterparts shall constitute one and the same instrument.


                                       4
<PAGE>
         16. Not an Offer. The submission of an unsigned copy of this Assignment
to Assignee for Assignee's consideration does not constitute an offer to assign
the Lease. This Assignment shall become effective and binding only upon the
execution and delivery of this Assignment by Assignor and Assignee.

         IN WITNESS WHEREOF, Assignor and Assignee execute this Assignment under
seal as of January 17, 2002.

ACUSPHERE, INC.                         THE GENERAL HOSPITAL CORPORATION

By: /s/ James R. Fitzgerald, Jr.        By: /s/ Sally Mason Boemer
   -----------------------------------     ---------------------------------
Name:  James R. Fitzgerald, Jr.         Name:  Sally Mason Boemer
Title: Senior Vice President            Title: Vice President, Finance
Date:  January 17, 2002                 Date:  January 9, 2002
Hereunto duly authorized                Hereunto duly authorized


                                       5
<PAGE>
                                    EXHIBIT A

                                      Lease


                                       6
<PAGE>
                                    EXHIBIT B

                               Hazardous Chemicals

I.       Assignor will take the following actions:

         (a)      Arrange for and cause the removal of all waste materials and
                  hazardous substances generated, acquired or otherwise handled
                  by Assignor during the Term from the Premises, including
                  without limitation wiping down bench tops, sinks, and other
                  horizontal surfaces with water and appropriate soaps or
                  cleansers.

         (b)      Retain a qualified environmental contractor to collect waste
                  materials and hazardous substances and to provide Assignor
                  with a receipt for said materials, and, as appropriate,
                  manifests for shipment and proper disposal.

         (c)      Provide Assignee and Landlord with copies of receipts and/or
                  manifests for removal and disposal of such waste materials and
                  hazardous substances removed pursuant to this Exhibit B.


                                       7
<PAGE>
                                    EXHIBIT C

                 WORK TO BE PERFORMED AND CONDITION OF PREMISES

GENERAL

Unless otherwise noted, Assignor shall have removed all of its furniture,
equipment and supplies (as further described in Section 3 (b) of the Assignment
and Assumption of Lease) and the Premises shall be broom clean. Any damage to
the Premises caused by such removal shall be repaired by Assignor including
spackling of any holes in the walls resulting from the removal of equipment,
furniture or personal effects. Notwithstanding the foregoing, Assignor shall not
be required to remove, and shall not remove, the HVAC and emergency generator
located on the roof of the Building, nor the panel and controls associated
therewith, which panel and controls are located in the Premises.

All chip tanks are to be emptied and cleaned and made ready by Assignor for
re-charging by Assignee.

All connections of the equipment to power, water or other systems shall be
stubbed at the equipment connection and left hanging in the space.

Assignor shall not remove any of the following items:

         1. Shelving attached to the walls
         2. Lab coat hooks
         3. Lab benches attached to the floor or wall
         4. Built-in cabinetry in the copy areas (off of Lab 2 and in the
            separate office area) and the conference room (in the separate
            office area)
         5. Fire extinguishers
         6. All existing snorkels to remain.

CLEAN ROOM

Hoist in ceiling of room to be removed.
One chemical fume hood to remain
Laminar flow hood to be removed

LAB 1
One chemical fume hood to remain.
All copper tubing connecting the gases to the equipment shall be removed.
The water filters will be removed from Lab 1. (These filters are associated with
the controlled humidity incubators and must stay with the incubators.)


                                       8
<PAGE>
LAB 2

Vent for halogenated waste shall remain. Assignor shall be responsible for the
removal of all chemicals.
One chemical fume hood to remain

LAB 4

Two chemical fume hoods to remain. (One exists (a walk in) and the other (a
benchtop hood) shall be re-installed by Assignor.)

LAB 5

Eye wash system to remain.
One chemical fume hood to remain.
In consideration of $5,500.00, to be paid by Assignee to Assignor on the
Effective Date, the de-ionized water system shall remain at the Premises and
upon receipt by Assignor of such amount, all right, title and interest therein
shall be conveyed from Assignor to Assignee. Landlord agrees that Assignee may,
but will not be required to, remove the de-ionized water system at the time of
termination of the Lease.
Dishwasher, autoclave, laminar containment hood shall be removed from the
Premises

Separate Office area - Conference Room

Two built in credenzas to remain
Projector screen to remain.

Separate Office area - Office in rear of space

Built-in desk to remain.  Shelving to remain.


                                       9