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                                                                   Exhibit 10.11

                             MASTER LEASE AGREEMENT

COMDISCO, INC. - LESSOR

MASTER LEASE AGREEMENT DATED MAY 1, 1995 BY AND BETWEEN COMDISCO, INC.
("LESSOR") AND ACUSPHERE, INC. ("LESSEE").

IN CONSIDERATION OF THE MUTUAL AGREEMENTS DESCRIBED BELOW, THE PARTIES AGREE AS
FOLLOWS (ALL CAPITALIZED TERMS ARE DEFINED IN SECTION 14.19):

1.   PROPERTY LEASED.

     Lessor leases to Lessee all of the Equipment described on each Schedule. In
the event of a conflict, the terms of a Schedule prevail over this Master Lease.

2.   TERM.

     On the Commencement Date, Lessee will be deemed to accept the Equipment,
will be bound to its rental obligations for each item of Equipment and the term
of a Schedule will begin and continue through the Initial Term and thereafter
until terminated by either party upon prior written notice received during the
Notice Period. No termination may be effective prior to the expiration of the
Initial Term.

3.   RENT AND PAYMENT.

     Rent is due and payable in advance, in immediately available funds, on the
first day of each Rent interval to the payee and at the location specified in
Lessor's invoice. Interim Rent is due and payable when invoiced. If any payment
is not made when due, Lessee will pay interest at the Overdue Rate. Upon
Lessee's execution of each Schedule, Lessee will pay Lessor the Advance
specified on the Schedule. The Advance will be credited towards the final Rent
payment if Lessee is not then in default. No interest will be paid on the
Advance.

4.   SELECTION; WARRANTY AND DISCLAIMER OF WARRANTIES.

     4.1  SELECTION. Lessee acknowledges that it has selected the Equipment and
disclaims any reliance upon statements made by the Lessor.

     4.2  WARRANTY AND DISCLAIMER OF WARRANTIES. Lessor warrants to Lessee that,
so long as Lessee is not in default, Lessor will not disturb Lessee's quiet and
peaceful possession, and unrestricted use of the Equipment. To the extent
permitted by the manufacturer, Lessor assigns to Lessee during the term of the
Schedule any manufacturer's warranties for the Equipment. LESSOR MAKES NO OTHER
WARRANTY, EXPRESS OR IMPLIED AS TO ANY MATTER WHATSOEVER, INCLUDING, WITHOUT
LIMITATION, THE MERCHANTABILITY OF THE EQUIPMENT OR ITS FITNESS FOR A PARTICULAR
PURPOSE. Lessor is not responsible for any liability, claim, loss, damage or
expense of any kind (including strict liability in tort) caused by the Equipment
except for any loss or damage caused by the negligent acts of Lessor. In no
event is Lessor responsible for special, incidental or consequential damages.

5.   TITLE; RELOCATION OR SUBLEASE; AND ASSIGNMENT.

     5.1  TITLE. Lessee holds the Equipment subject and subordinate to the
rights of the Owner, Lessor, any Assignee and any Secured Party. Lessee
authorizes Lessor, as Lessee's agent, to prepare, execute and file in Lessee's
name precautionary Uniform Commercial Code financing statements showing the
interest of the Owner, Lessor, and any Assignee or Secured Party in the
Equipment and to insert serial numbers in Schedules as appropriate. Lessee will,
at its expense, keep the Equipment free and clear from any liens or encumbrances
of any kind (except any caused by Lessor) and will indemnify and hold Lessor,
Owner, any Assignee and Secured Party harmless from and against any loss caused
by Lessee's failure to do so.

     5.2  RELOCATION OR SUBLEASE. Upon prior written consent, Lessee may
relocate Equipment to any location within the continental United States provided
(i) the Equipment will not be used by an entity exempt from federal income tax,
(ii) all additional costs (including any administrative fees, additional taxes
and insurance coverage) are reconciled and promptly paid by Lessee.

     Lessee may sublease the Equipment upon the reasonable consent of the Lessor
and the Secured Party. Such consent to sublease will be granted if: (i) Lessee
meets the relocation requirements set out above, (ii) the sublease is expressly
subject and subordinate to the terms of this schedule, (iii) Lessee assigns its
rights in the sublease to Lessor and the Secured Party as additional collateral
and security, (iv) Lessee's obligation to maintain and insure the Equipment is
not altered, (v) all financing statements required to continue the Secured
Party's prior perfected security interest are filed, and (vi) the sublease is
not to a leasing entity affiliated with the manufacturer of the Equipment
described on the Schedule. Lessor acknowledges Lessee's right to sublease for a
term which extends beyond the expiration of the Initial Term. If Lessee
subleases the Equipment for a term extending beyond the expiration of such
Initial Term of the applicable Schedule, Lessee will remain obligated upon the
expiration of the Initial Term to return such Equipment, or, at Lessor's sole

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discretion to (i) return Like Equipment or (ii) negotiate a mutually acceptable
lease extension or purchase. If the parties cannot mutually agree upon the terms
of an extension or purchase, the term of the Schedule will extend upon the
original terms and conditions until terminated pursuant to Section 2.

     No relocation or sublease will relieve Lessee from any of its obligations
under this Master Lease and the relevant Schedule.

     5.3  ASSIGNMENT BY LESSOR. The terms and conditions of each Schedule have
been fixed by Lessor in order to permit Lessor to sell and/or assign or transfer
its interest or grant a security interest in each Schedule and/or the Equipment
to a Secured Party or Assignee. In that event, the term Lessor will mean the
Assignee and any Secured Party. However, any assignment, sale, or other transfer
by Lessor will not relieve Lessor of its obligations to Lessee and will not
materially change Lessee's duties or materially increase the burdens or risks
imposed on Lessee. The Lessee consents to and will acknowledge such assignments
in a written notice given to Lessee. Lessee also agrees that:

     (a)  The Secured Party will be entitled to exercise all of Lessor's rights,
          but will not be obligated to perform any of the obligations of Lessor.
          The Secured Party will not disturb Lessee's quiet and peaceful
          possession and unrestricted use of the Equipment so long as Lessee is
          not in default and the Secured Party continues to receive all Rent
          payable under the Schedule; and

     (b)  Lessee will pay all Rent and all other amounts payable to the Secured
          Party, despite any defense or claim which it has against Lessor.
          Lessee reserves its right to have recourse directly against Lessor for
          any defense or claim;

     (c)  Subject to and without impairment of Lessee's leasehold rights in the
          Equipment, Lessee holds the Equipment for the Secured Party to the
          extent of the Secured Party's rights in that Equipment.

6.   NET LEASE; TAXES AND FEES.

     6.1  NET LEASE. Each Schedule constitutes a net lease. Lessee's obligation
to pay Rent and all other amounts is absolute and unconditional and is not
subject to any abatement, reduction, set-off, defense, counterclaim,
interruption, deferment or recoupment for any reason whatsoever.

     6.2  TAXES AND FEES. Lessee will pay when due or reimburse Lessor for all
taxes, fees or any other charges (together with any related interest or
penalties not arising from the negligence of Lessor) accrued for or arising
during the term of each Schedule against Lessor, Lessee or the Equipment by any
governmental authority (except only Federal, state and local taxes on the
capital or the net income of Lessor). Lessor will file all personal property tax
returns for the Equipment and pay all property taxes due. Lessee will reimburse
Lessor for property taxes within thirty (30) days of receipt of an invoice.

7.   CARE, USE AND MAINTENANCE; ATTACHMENTS AND RECONFIGURATIONS; AND INSPECTION
     BY LESSOR.

     7.1  CARE, USE AND MAINTENANCE. Lessee will maintain the Equipment in good
operating order and appearance, protect the Equipment from deterioration, other
than normal wear and tear, and will not use the Equipment for any purpose other
than that for which it was designed. If commercially available, Lessee will
maintain in force a standard maintenance contract with the manufacturer of the
Equipment, or another party acceptable to Lessor, and will provide Lessor with a
complete copy of that contract. If Lessee has the Equipment maintained by a
party other than the manufacturer, Lessee agrees to pay any costs necessary for
the manufacturer to bring the Equipment to then current release, revision and
engineering change levels, and to re-certify the Equipment as eligible for
manufacturer's maintenance at the expiration of the lease term. The lease term
will continue upon the same terms and conditions until recertification has been
obtained.

     7.2  ATTACHMENTS AND RECONFIGURATIONS. Upon receiving the prior written
consent of Lessor, Lessee may reconfigure and install Attachments on the
Equipment. In the event of such a Reconfiguration or Attachment, Lessee will,
upon return of the Equipment, at its expense, restore the Equipment to the
original configuration specified on the Schedule in accordance with the
manufacturer's specifications and in the same operating order, repair and
appearance as when installed (normal wear and tear excluded). If any parts of
the Equipment are removed during a Reconfiguration or Attachment, Lessor may
require Lessee to provide additional security, satisfactory to the Lessor, in
order to ensure performance of Lessee's obligations set forth in this
subsection. Neither Attachments nor parts installed on Equipment in the course
of Reconfiguration will be accessions to the Equipment.

     7.3  INSPECTION BY LESSOR. Upon request, Lessee, during reasonable business
hours and subject to Lessee's security requirements, will make the Equipment and
its related log and maintenance records available to Lessor for inspection.

8.   REPRESENTATIONS AND WARRANTIES OF LESSEE. Lessee hereby represents,
warrants and covenants that with respect to the Master Lease and each Schedule
executed hereunder:

     (a)  The Lessee is a corporation duly organized and validly existing in
          good standing under the laws of the jurisdiction of its incorporation,
          is duly qualified to do business in each jurisdiction (including the
          jurisdiction where the Equipment is, or is to be, located) where its
          ownership or lease of property or the conduct of its business requires
          such qualification; and has full corporate power and authority to

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          hold property under the Master Lease and each Schedule and to enter
          into and perform its obligations under such Lease.

     (b)  The execution and delivery by the Lessee of the Master Lease and each
          Schedule and its performance thereunder have been duly authorized by
          all necessary corporate action on the part of the Lessee, and the
          Master Lease and each Schedule are not inconsistent with the Lessee's
          Certificate of Incorporation or Bylaws, do not contravene any law or
          governmental rule, regulation or order applicable to it, do not and
          will not contravene any provision of, or constitute a default under,
          any indenture, mortgage, contract or other instrument to which it is a
          party or by which it is bound, and the Master Lease and each Schedule
          constitute legal, valid and binding agreements of the Lessee,
          enforceable in accordance with their terms.

     (c)  There are no actions, suits, proceedings or patent claims pending or,
          to the knowledge of the Lessee, threatened against or affecting the
          Lessee in any court or before any governmental commission, board or
          authority which, if adversely determined, will have a material adverse
          effect on the ability of the Lessee to perform its obligations under
          the Master Lease and each Schedule.

     (d)  The Equipment is personal property and when subjected to use by the
          Lessee will not be or become fixtures under applicable law.

     (e)  The Lessee has no material liabilities or obligations, absolute or
          contingent (individually or in the aggregate), except the liabilities
          and obligations of the Lessee as set forth in the Financial Statements
          and liabilities and obligations which have occurred in the ordinary
          course of business, and which have not been, in any case or in the
          aggregate, materially adverse to Lessee's going business.

     (f)  To the best of the Lessee's knowledge, the Lessee owns, possesses, has
          access to, or can become licensed on reasonable terms under all
          patents, patent applications, trademarks, trade names, inventions,
          franchises, licenses, permits, computer software and copyrights
          necessary for the operations of its business as now conducted, with no
          known infringement of, or conflict with, the rights of others.

     (g)  All material contracts, agreements and instruments to which the Lessee
          is a party are in full force and effect in all material respects, and
          are valid, binding and enforceable by the Lessee in accordance with
          their respective terms, subject to the effect of applicable bankruptcy
          and other similar laws affecting the rights of creditors generally,
          and rules of law concerning equitable remedies.

9.   DELIVERY AND RETURN OF EQUIPMENT.

     Lessee hereby assumes the full expense of transportation and in-transit
insurance to Lessee's premises and installation thereat of the Equipment. Upon
termination (by expiration or otherwise) of each Schedule, Lessee shall,
pursuant to Lessor's instructions and at Lessee's full expense (including,
without limitation, expenses of transportation and in-transit insurance), return
the Equipment to Lessor in the same operating order, repair, condition and
appearance as when received, less normal depreciation and wear and tear. Lessee
shall return the Equipment to Lessor at its address set forth herein or at such
other address within the continental United States as directed by Lessor,
provided, however, that Lessee's expense shall be limited to the cost of
returning the equipment to Lessor's address as set forth herein. During the
period subsequent to receipt of a notice under Section 2, Lessor may demonstrate
the Equipment's operation in place and Lessee will supply any of its personnel
as may reasonably be required to assist in the demonstrations.

10.  LABELING.

     Upon request, Lessee will mark the Equipment indicating Lessor's interest.
Lessee will keep all Equipment free from any other marking or labeling which
might be interpreted as a claim of ownership.

11.  INDEMNITY.

     Lessee will indemnify and hold Lessor, any Assignee and any Secured Party
harmless from and against any and all claims, costs, expenses, damages and
liabilities, including reasonable Attorneys' fees, arising out of the ownership
(for strict liability in tort only), selection, possession, leasing, operation,
control, use, maintenance, delivery, return or other disposition of the
Equipment. However, Lessee is not responsible to a party indemnified hereunder
for any claims, costs, expenses, damages and liabilities occasioned by the
negligent acts of such indemnified party. Lessee agrees to carry bodily injury
and property damage liability insurance during the term of the Master Lease in
amounts and against risks customarily insured against by the Lessee on equipment
owned by it. Any amounts received by Lessor under that insurance will be
credited against Lessee's obligations under this Section.

12.  RISK OF LOSS.

     Effective upon delivery and until the Equipment is returned, Lessee
relieves Lessor of responsibility for all risks of physical damage to or loss or
destruction of the Equipment. Lessee will carry casualty insurance for each item
of Equipment in an amount not less than the Casualty Value. All policies for
such insurance will name the Lessor and any Secured Party as additional insured
and as loss payee, and will provide for at least thirty (30) days prior written
notice to the Lessor of cancellation or expiration, and will insure Lessor's

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interests regardless of any breach or violation by Lessee of any representation,
warranty or condition contained in such policies and will be primary without
right of contribution from any insurance effected by Lessor. Upon the execution
of any Schedule, the Lessee will furnish appropriate evidence of such insurance
acceptable to Lessor.

     Lessee will promptly repair any damaged item of Equipment unless such
Equipment has suffered a Casualty Loss. Within fifteen (15) days of a Casualty
Loss, Lessee will provide written notice of that loss to Lessor and Lessee will,
at Lessor's option, either (a) replace the item of Equipment with Like Equipment
and marketable title to the Like Equipment will automatically vest in Lessor or
(b) pay the Casualty Value and after that payment and the payment of all other
amounts due and owing, Lessee's obligation to pay further Rent for the item of
Equipment will cease.

13.  DEFAULT, REMEDIES AND MITIGATION.

     13.1 DEFAULT. The occurrence of any one or more of the following Events of
Default constitutes a default under a Schedule:

     (a)  Lessee's failure to pay Rent or other amounts payable by Lessee when
          due if that failure continues for five (5) days after written notice;
          or

     (b)  Lessee's failure to perform any other term or condition of the
          Schedule or the material inaccuracy of any representation or warranty
          made by the Lessee in the Schedule or in any document or certificate
          furnished to the Lessor hereunder if that failure or inaccuracy
          continues for ten (10) days after written notice; or

     (c)  An assignment by Lessee for the benefit of its creditors, the failure
          by Lessee to pay its debts when due, the insolvency of Lessee, the
          filing by Lessee or the filing against Lessee of any petition under
          any bankruptcy or insolvency law or for the appointment of a trustee
          or other officer with similar powers, the adjudication of Lessee as
          insolvent, the liquidation of Lessee, or the taking of any action for
          the purpose of the foregoing; or

     (d)  The occurrence of an Event of Default under any Schedule or other
          agreement between Lessee and Lessor or its Assignee or Secured Party.

     13.2 REMEDIES. Upon the occurrence of any of the above Events of Default,
Lessor, at its option, may:

     (a)  enforce Lessee's performance of the provisions of the applicable
          Schedule by appropriate court action in law or in equity;

     (b)  recover from Lessee any damages and or expenses, including Default
          Costs;

     (c)  with notice and demand, recover all sums due and accelerate and
          recover the present value of the remaining payment stream of all Rent
          due under the defaulted Schedule (discounted at the same rate of
          interest at which such defaulted Schedule was discounted with a
          Secured Party plus any prepayment fees charged to Lessor by the
          Secured Party or, if there is no Secured Party, then discounted at 6%)
          together with all Rent and other amounts currently due as liquidated
          damages and not as a penalty;

     (d)  with notice and process of law and in compliance with Lessee's
          security requirements, Lessor may enter on Lessee's premises to remove
          and repossess the Equipment without being liable to Lessee for damages
          due to the repossession, except those resulting from Lessor's, its
          assignees', agents' or representatives' negligence; and

     (e)  pursue any other remedy permitted by law or equity.

     The above remedies, in Lessor's discretion and to the extent permitted by
law, are cumulative and may be exercised successively or concurrently.

     13.3 MITIGATION. Upon return of the Equipment pursuant to the terms of
Section 13.2, Lessor will use its best efforts in accordance with its normal
business procedures (and without obligation to give any priority to such
Equipment) to mitigate Lessor's damages as described below. EXCEPT AS SET FORTH
IN THIS SECTION, LESSEE HEREBY WAIVES ANY RIGHTS NOW OR HEREAFTER CONFERRED BY
STATUTE OR OTHERWISE WHICH MAY REQUIRE LESSOR TO MITIGATE ITS DAMAGES OR MODIFY
ANY OF LESSOR'S RIGHTS OR REMEDIES STATED HEREIN. Lessor may sell, lease or
otherwise dispose of all or any part of the Equipment at a public or private
sale for cash or credit with the privilege of purchasing the Equipment. The
proceeds from any sale, lease or other disposition of the Equipment are defined
as either:

     (a)  if sold or otherwise disposed of, the cash proceeds less the Fair
          Market Value of the Equipment at the expiration of the Initial Term
          less the Default Costs; or

     (b)  if leased, the present value (discounted at three points over the
          prime rate as referenced in the Wall Street Journal at the time of the
          mitigation) of the rentals for a term not to exceed the Initial Term,
          less the Default Costs.

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     Any proceeds will be applied against liquidated damages and any other sums
due to Lessor from Lessee. However, Lessee is liable to Lessor for, and Lessor
may recover, the amount by which the proceeds are less than the liquidated
damages and other sums due to Lessor from Lessee.

14.  ADDITIONAL PROVISIONS.

     14.1 BOARD ATTENDANCE. Lessor or its duly appointed representative will
have the right to attend Lessee's corporate Board of Directors meetings and
Lessee will give Lessor reasonable notice in advance of any special Board of
Directors meeting, which notice will provide an agenda of the subject matter to
be discussed at such board meeting. Lessee will provide Lessor with a certified
copy of the minutes of each Board of Directors meeting within thirty (30) days
following the date of such meeting held during the term of this Lease.

     14.2 FINANCIAL STATEMENTS. Lessee will provide to Lessor the financial
statements specified in this Section, prepared in accordance with generally
accepted accounting principles, consistently applied (the "Financial
Statements"); provided, however, after the effective date of the initial
registration statement covering a public offering of Lessee's securities, the
term "Financial Statements" will be deemed to refer to only those statements
required by the Securities and Exchange Commission, to be provided no less
frequently than quarterly. Lessee will provide to Lessor (i) as soon as
practicable (within (30) days) after the end of each month, the same information
which Lessee provides to its Board of Directors, but which will include not less
than a monthly income statement, balance sheet and statement of cash flows,
certified by Lessee's Chief Executive or Financial Officer to be true and
correct; and (ii) as soon as practicable (and in any event within ninety (90)
days) after the end of each fiscal year, audited balance sheets as of the end of
such year (consolidated if applicable), and related statements of income or
loss, retained earnings or deficit and changes in the financial position and
capital structure of Lessee for such year, setting forth in comparative form the
corresponding figures for the preceding fiscal year, and accompanied by an audit
report and opinion of the independent certified public accountants selected by
Lessee. Lessee will promptly furnish to Lessor any additional information
(including but not limited to tax returns, income statements, balance sheets,
and names of principal creditors) as Lessor reasonably believes necessary to
evaluate Lessee's continuing ability to meet financial obligations.

     14.3 OBLIGATIONS TO LEASE ADDITIONAL EQUIPMENT. Upon notice to Lessee,
Lessor will not be obligated to lease any Equipment which would have a
commencement Date after said notice if: (i) Lessee is in default under this
Master Lease or any Schedule; (ii) Lessee is in default under any loan
agreement, the result of which would allow the lender or any secured party to
demand immediate payment of the indebtedness; (iii) there is a material adverse
change in Lessee's credit standing; or (iv) Lessor determines (in reasonable
good faith) that Lessee will be unable to perform its obligations under this
Master Lease.

     14.4 MERGER AND SALE PROVISIONS. Lessee will notify Lessor of any proposed
Merger at least sixty (60) days prior to the closing date. Lessor may, in its
discretion, either (i) consent to the assignment of the Master Lease and all
relevant Schedules to the successor entity, or (ii) terminate the Master Lease
and all relevant Schedules. If Lessor elects to consent to the assignment,
Lessee and its successor will sign the assignment documentation provided by
Lessor. If Lessor elects to consent to the assignment, Lessee and its successor
will sign the assignment documentation provided by Lessor. If Lessor elects to
terminate the Master Lease and all relevant Schedules, then Lessee will pay
Lessor all amounts then due and owing and a termination fee equal to the present
value (discounted at 6%) of the remaining Rent for the balance of the Initial
Term(s) of all Schedules, and will return the Equipment in accordance with
Section 9.

     14.5 ENTIRE AGREEMENT. This Master Lease and associated Schedules supersede
all other oral or written agreements or understandings between the parties
concerning the Equipment including, for example, purchase orders. ANY AMENDMENT
OF THIS MASTER LEASE OR A SCHEDULE, MAY ONLY BE ACCOMPLISHED BY A WRITING SIGNED
BY THE PARTY AGAINST WHOM THE AMENDMENT IS SOUGHT TO BE ENFORCED.

     14.6 NO WAIVER. No action taken by Lessor or Lessee will be deemed to
constitute a waiver of compliance with any representation, warranty or covenant
contained in this Master Lease or a Schedule. The waiver by Lessor or Lessee of
a breach of any provision of this Master Lease or a Schedule will not operate or
be construed as a waiver of any subsequent breach.

     14.7 BINDING NATURE. Each Schedule is binding upon, and inures to the
benefit of Lessor and its assigns. LESSEE MAY NOT ASSIGN ITS RIGHTS OR
OBLIGATIONS.

     14.8 SURVIVAL OF OBLIGATIONS. All agreements, obligations including, but
not limited to those arising under Section 6.2, representations and warranties
contained in this Master Lease, any Schedule or in any document delivered in
connection with those agreements are for the benefit of Lessor and any Assignee
or Secured Party and survive the execution, delivery, expiration or termination
of this Master Lease.

     14.9 NOTICES. Any notice, request or other communication to either party by
the other will be given in writing and deemed received upon the earlier of
actual receipt or three days after mailing if mailed postage prepaid by regular
or airmail to Lessor (to the attention of "Lease Administrator") or Lessee, at
the address set out in the Schedule or, one day after it is sent by courier or
on the same day as sent via facsimile transmission, provided that the original
is sent by personal delivery or mail by the receiving party.

     14.10 APPLICABLE LAW. THIS MASTER LEASE HAS BEEN, AND EACH SCHEDULE WILL
HAVE BEEN MADE, EXECUTED AND DELIVERED IN THE STATE OF ILLINOIS AND WILL BE
GOVERNED AND CONSTRUED FOR ALL PURPOSES IN ACCORDANCE WITH THE LAWS OF THE STATE
OF ILLINOIS WITHOUT GIVING EFFECT TO CONFLICT OF LAW PROVISIONS. NO RIGHTS OR
REMEDIES

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REFERRED TO IN ARTICLE 2A OF THE UNIFORM COMMERCIAL CODE WILL BE CONFERRED ON
LESSEE UNLESS EXPRESSLY GRANTED IN THIS MASTER LEASE OR A SCHEDULE.

     14.11 SEVERABILITY. If any one or more of the provisions of this Master
Lease or any schedule is for any reason held invalid, illegal or unenforceable,
the remaining provisions of this Master Lease and any such Schedule will be
unimpaired, and the invalid, illegal or unenforceable provision replaced by a
mutually acceptable valid, legal and enforceable provision that is closest to
the original intention of the parties.

     14.12 COUNTERPARTS. This Master Lease and any Schedule may be executed in
any number of counterparts, each of which will be deemed an original, but all
such counterparts together constitute one and the same instrument. If Lessor
grants a security interest in all or any part of a Schedule, the Equipment or
sums payable thereunder, only that counterpart Schedule marked "Secured Party's
Original" can transfer Lessor's rights and all other counterparts will be marked
"Duplicate".

     14.13 NONSPECIFIED FEATURES AND LICENSES PRODUCTS. If the Equipment is
supplied from Lessor's inventory and contains any features not specified in the
Schedule, Lessee grants Lessor the right to remove any such features. Any
removal will be performed by the manufacturer or another party acceptable to
Lessee, upon the request of Lessor, at a time convenient to Lessee, provided
that Lessee will not unreasonably relay the removal of such features.

     Lessee will obtain no title to Licensed Products which will at all times
remain the property of the owner of the Licensed Products. A license from the
owner may be required and it is Lessee's responsibility to obtain any required
license before the use of the Licensed Products. Lessee agrees to treat the
Licensed Products as confidential information of the owner, to observe all
copyright restrictions, and not to reproduce or sell the Licensed Products.

     14.14 ADDITIONAL DOCUMENTS. Lessee will, upon execution of this Master
Lease and as may be requested thereafter, provide Lessor with a secretary's
certificate of incumbency and authority and any other documents reasonably
requested by Lessor. Upon the execution of each Schedule with a purchase price
in excess of $1,000,000, Lessee will provide Lessor with an opinion from
Lessee's counsel in a form acceptable to Lessor regarding the representations
and warranties in Section 8.

     14.15 ELECTRONIC COMMUNICATIONS. Each of the parties may communicate with
the other by electronic means under mutually agreeable terms.

     14.16 LESSOR'S RIGHT TO MATCH. Lessee's rights under Section 5.2 and 7.2
are subject to Lessor's right to match any sublease or upgrade proposed by a
third party. Lessee will provide Lessor with the terms of the third party offer
and Lessor will have three (3) business days to match the offer. Lessee will
obtain such upgrade from or sublease the Equipment to Lessor if Lessor has
timely matched the third party offer.

     14.17 LANDLORD/MORTGAGEE WAIVER. Lessee agrees to provide Lessor with a
Landlord/Mortgagee Waiver with respect to the Equipment. Such waiver shall be in
a form satisfactory to Lessor.

     14.18 EQUIPMENT PROCUREMENT CHARGES/PROGRESS PAYMENTS. Lessee hereby agrees
that Lessor shall not, by virtue of its entering into this Lease, be required to
remit any payments in any manufacturer or other third party until Lessee accepts
the Equipment subject to this Lease.

     14.19 DEFINITIONS.

ADVANCE - means the amount due to Lessor by Lessee upon Lessee's execution of
each Schedule.

ASSIGNEE - means an entity to whom Lessor has sold or assigned its rights as
owner and Lessor of Equipment.

ATTACHMENT - means any accessory, equipment or device and the installation
thereof that does not impair the original function or use of the Equipment and
is capable of being removed without causing material damage to the Equipment and
is not an accession to the Equipment.

CASUALTY LOSS - means the irreparable loss or destruction of Equipment.

CASUALTY VALUE - means the greater of the aggregate Rent remaining to be paid
for the balance of the lease term or the Fair Market Value of the Equipment
immediately prior to the Casualty Loss. However, if a Casualty Value Table is
attached to the relevant Schedule its terms will control.

COMMENCEMENT CERTIFICATE - means the Lessor provided certificate which must be
signed by Lessee within ten (10) days of the Commencement Date as requested by
Lessor.

COMMENCEMENT DATE - is defined in each Schedule.

DEFAULT COSTS - means reasonable attorney's fees and remarketing costs resulting
from a Lessee default or Lessor's enforcement of its remedies.

EQUIPMENT - means the property described on a Schedule and any replacement of
that property required or permitted by this Master Lease or a Schedule but not
including any Attachment.

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EVENT OF DEFAULT - means the events described in Subsection 13.1.

FAIR MARKET VALUE - means the aggregate amount which would be obtainable in an
arm's length transaction between an informed and willing buyer/user and an
informed and willing seller under no compulsion to sell.

INITIAL TERM - means the period of time beginning on the first day of the first
full Rent Interval following the Commencement Date for all items of Equipment
and continuing for the number of Rent Intervals indicated on a Schedule.

INSTALLATION DATE - means the day on which Equipment is installed and qualified
for a commercially available manufacturer's standard maintenance contract or
warranty coverage, if available.

INTERIM RENT - means the pro-rata portion of Rent due for the period from the
Commencement Date through but not including the first day of the first full Rent
Interval included in the Initial Term.

LICENSED PRODUCTS - means any software or other licensed products attached to
the Equipment.

LIKE EQUIPMENT - means replacement Equipment which is lien free and of the same
model, type, configuration and manufacture as Equipment.

LIKE PART - means a substituted part which is lien free and of the same
manufacturer and part number as the removed part, and which when installed on
the Equipment will be eligible for maintenance coverage with the manufacturer of
the Equipment.

MERGER - means any consolidation or merger of the Lessee with or into any other
corporation or entity, any sale or conveyance of all or substantially all of the
assets of the Lessee to any other person or entity or any stock acquisition of
the Lessee by any other person or entity.

NOTICE PERIOD - means the time period described in a Schedule during which
Lessee may give Lessor notice of the termination of the term of that Schedule.

OVERDUE RATE - means the lesser of five percent (5%) of the payment due or the
maximum rate permitted by the law of the state where the Equipment is located.

OWNER - means the owner of Equipment.

RECONFIGURATION - means any change to Equipment that would upgrade or downgrade
the performance capabilities of the Equipment in any way.

RENT - means the rent, including Interim Rent, Lessee will pay for each item of
Equipment expressed in a Schedule either as a specific amount or an amount equal
to the amount which Lessor pays for an item of Equipment multiplied by a lease
rate factor plus all other amounts due to Lessor under this Master Lease or a
Schedule.

RENT INTERVAL - means a full calendar month or quarter as indicated on a
Schedule.

SCHEDULE - means an Equipment Schedule which incorporates all of the terms and
conditions of this Master Lease and, for purposes of Section 14.12, its
associated Commencement Certificate(s).

SECURED PARTY - means an entity to whom Lessor has granted a security interest
in a Schedule and related Equipment for the purpose of securing a loan.

     IN WITNESS WHEREOF, the parties hereto have executed this Master Lease on
or as of the day and year first above written.

ACUSPHERE, INC.                 COMDISCO, INC.
as Lessee                       as Lessor

By: /s/ Sherri C. Oberg         By: /s/ James Labe
    -------------------------       --------------------------------------------
    Title: President and CEO        Title: President, Comdisco Ventures Division

                                                                         3/18/95


                                       7
<PAGE>   8

                                   ADDENDUM TO
                 MASTER LEASE AGREEMENT DATED AS OF MAY 1, 1995
                       BETWEEN ACUSPHERE, INC., AS LESSEE
                          AND COMDISCO, INC., AS LESSOR


The undersigned hereby agree that the terms and conditions of the
above-referenced Master Lease are hereby modified and amended as follows:

(a)  SECTION 4.2, WARRANTY AND DISCLAIMER OF WARRANTIES.

     In line 2 after the word "default", add the words "under this Master Lease
     Agreement or the relevant Schedule".

(b)  SECTION 5.1, TITLE.

     In line 6 after the word "Lessor" in the parenthetical, add the words",
     owner or any assignee."

(c)  SECTION 5.2, RELOCATION OR SUBLEASE.

     In line 1 after the word "consent", add the words "of Lessor".

(d)  SECTION 5.3, ASSIGNMENT BY LESSOR.

     To the end of the first paragraph, add the words", in the event Lessor has
     granted a security interest in a Schedule and related Equipment to a
     Secured Party and has given notice thereof to the Lessee:".

     In line 3 of subsection (a) after the word "default", add the words "under
     this Master Lease Agreement or the relevant Schedule".

(e)  SECTION 6.2, TAXES AND FEES.

     In line 2 after the word "Lessor" in the parenthetical, add the words
     ", owner or any assignee"; in line 4 after the word "Lessor" in the
     parenthetical, add the words", owner or any assignee".

(f)  SECTION 8, REPRESENTATIONS AND WARRANTIES OF LESSEE.

     In Subsection (b), line 3, after the word "Schedule", delete the words "are
     not inconsistent with" and replace with the words "do not contravene"; in
     line 5 before the word "indenture", insert the word "material", in line 7
     after the word "enforceable", add the words "against Lessee".

     Delete Subsection (f) in its entirety and replace with the following:

     "Except as otherwise disclosed to Lessor, Lessee is not aware of any
     infringement of, or conflict with, the rights of others in regards to any
     patents, patent applications, trademarks, trade names, inventions,
     franchises, licenses, permits, computer software and/or copyrights
     necessary for the operation of its business as now conducted."

(h)  SECTION 9, DELIVERY AND RETURN OF EQUIPMENT.

     Delete second, third and fourth sentences in their entirety.

<PAGE>   9

(i)  SECTION 11, INDEMNITY.

     In line 6 after the word "acts', add the words", willful misconduct or bad
     faith".

(j)  SECTION 13.1, DEFAULT.

     In line 1 of Subsection (b) after the word "inaccuracy", add the words
     "when made".

     In line 4 of Subsection (c) after the word "powers", add the words "(which
     has not been dismissed or stayed within sixty (60) days)".

(k)  SECTION 13.3, REMEDIES.

     In line 4 of Section (d) after the word "negligence", add the words
     ", willful misconduct or bad faith,".

(l)  SECTION 13.2, MITIGATION.

     In lines 1 and 2 of Subsection (b), delete the words "three points over the
     prime rate as referenced in the Wall Street Journal at the time of the
     mitigation), replace with the words and number "six percent (6%)".

(m)  SECTION 14.1, BOARD ATTENDANCE.

     Add the following sentence to the end of Section 14.1: "Provided, however,
     the Board of Directors shall retain the right to meet in an executive
     session."

(n)  SECTION 14.2, FINANCIAL STATEMENTS.

     In line 10, delete the word and number "ninety (90)" and replace with the
     words and number "one hundred and twenty (120)"; in the next to last line,
     delete the word "believes" and replace with the words "requests as".

(o)  SECTION 14.3, OBLIGATION TO LEASE ADDITIONAL EQUIPMENT.

     In line 1 after the word "Upon", add the word "prior".

     In line 5, delete clause (iv) in its entirety and replace with the
     following:

     "(iv) Lessor determines (in reasonable good faith) that Lessee will be
     unable to perform its obligations under this Master Lease due to the loss
     of key employees/founders, Lessee's inability to secure necessary financing
     to continue operations, and/or extreme changes to existing business
     conditions."

(p)  SECTION 14.7, BINDING NATURE.

     At the beginning of the second sentence, add the words "Except as provided
     in Section 14.4,".

(q)  SECTION 14.8, SURVIVAL OF OBLIGATIONS.

     In the last line after the word "execution", delete the comma and add the
     word "or"; after the word "delivery", delete the words "expiration or
     termination"; Add a last sentence as follows: "The

                                      -2-
<PAGE>   10

     obligations of Sections 6.2, 9 and 11 shall survive the execution or
     termination of this Master Lease.

(r)  SECTION 14.16, LESSOR'S RIGHT TO MATCH.

     In line 2 after the word "party", add the words "as to Equipment that is
     currently on lease from Lessor to Lessee".

Except as amended hereby, all other terms and conditions of the Master Lease
Agreement remain in full force and effect.

This Addendum to Master Lease is executed this 24th day of November, 1999.

ACUSPHERE, INC.,                    COMDISCO, INC.,
AS LESSEE                           AS LESSOR

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

Title: President and CEO            Title: President, Comdisco Ventures Division
      ----------------------------        --------------------------------------

Date: 12/20/99                      Date: 1/6/00
     -----------------------------       ---------------------------------------


                                      -3-