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                                                                 EXHIBIT 10.33

                                 PROMISSORY NOTE

     FOR VALUE RECEIVED, on the Maturity Date, as such term is defined in
Section 1.1 below, ACUSPHERE, INC., a Delaware business corporation with its
chief executive office and principal place of business presently at 500 Arsenal
Street, Watertown, MA 02472 ("BORROWER") promises to pay to the order of
MASSACHUSETTS DEVELOPMENT FINANCE AGENCY, a body politic and corporate created
by Chapter 289 of The Acts of 1998 and established under Massachusetts General
Laws Chapter 23G as amended, ("LENDER") at its principal offices at 160 Federal
Street, Boston, MA 02110, or at such other place as the holder of this note may
from time to time designate in writing, the principal sum of TWO MILLION DOLLARS
($2,000,000.00) or such lesser amount advanced by Lender pursuant to Section 1.1
below, or so much thereof then remaining unpaid, in lawful money of the United
States with interest at the rate or rates set forth below, until fully paid.
Borrower further agrees to pay upon demand made after the occurrence and during
the continuance of an Event of Default, as such term is defined below, all
costs, including reasonable attorneys' fees reasonably incurred in the
collection of Borrower's obligations and the defense, preservation, enforcement
or protection of Lender's rights and remedies under this Note, or in the
foreclosure of any mortgage or security interest now or hereafter securing the
same or in any proceedings to otherwise enforce or protect upon an Event of
Default Lender's rights and remedies under this Note or any security therefor.
Interest on this Note shall be computed on the basis of a year of three hundred
sixty (360) days and actual days elapsed.

     1.0.     FUNDING; TERM; INTEREST RATE; PAYMENTS.

              1.1.    FUNDING; TERM. Borrower may request one (1) advance of up
     to the entire principal amount of this Note upon Lender's receipt from
     Borrower of those documents and satisfaction of those conditions precedent
     specified in that certain letter agreement by and among Borrower and Lender
     dated August 16, 2004 (the "Funding Requirements"), or upon the waiver of
     any such Funding Requirements, as determined in the Lender's sole
     discretion. Provided the Funding Requirements have been satisfied and no
     Event of Default exists on the date Lender receives such request for an
     advance and no event or circumstance exists on such date which with the
     passage time, or notice, or both would result in an Event of Default, the
     Lender shall advance the full requested amount within three (3) business
     days of such date (the "FUND DATE"). The term of this Note shall commence
     on the Fund Date and shall mature on the last day of the 120th calendar
     month following the Fund Date (the "MATURITY DATE").

              1.2.    PAYMENTS OF PRINCIPAL AND INTEREST. No payments shall be
     due and payable during the first twenty-four (24) months of the term of
     this Note (the "DEFERRAL PERIOD"). Thereafter, subject to the adjustment in
     payment provided in Section 1.4 below, payments of principal and interest
     at the rate provided in Section 1.3 below shall be made commencing on the
     first day of the calendar month next following the twenty-five (25) month
     anniversary of the Fund Date (the "PAYMENT START DATE") and continuing on
     the first day of each successive month thereafter through and including the
     Maturity Date at which time all remaining principal and accrued interest
     shall be paid. Each such payment of principal shall be equal to the
     aggregate outstanding Adjusted Principal Amount (hereinafter defined)
     divided by the number of monthly payments then remaining such that the
     Adjusted Principal Amount shall fully amortize over the balance of the term
     of this Note in equal installments. Each such payment of accrued interest
     shall be based on the rate provided in Section 1.3 (or, if applicable,
     Section 1.4) and shall be paid in arrears.

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              1.3.    INTEREST RATE. So long as no Event of Default (hereafter
     defined) has occurred and is continuing (but subject to applicable cure or
     grace periods), and subject to the terms hereof, the principal outstanding
     hereunder from time to time shall bear interest at the following rates:

              (a) from the Fund Date until the Payment Start Date, representing
     the Deferral Period, simple interest on the outstanding principal amount of
     this Note shall accrue at a rate of five percent (5%) per annum (herein,
     the "ACCRUED INTEREST AMOUNT"); and

              (b) beginning on the Payment Start Date, simple interest on the
     outstanding principal amount of this Note plus the outstanding Accrued
     Interest Amount shall accrue at a rate of five percent (5%) per annum
     (based upon a three hundred and sixty (360) day year and actual days
     elapsed). The sum of the principal of this Note and the Accrued Interest
     Amount at any time then outstanding shall be referred to herein as the
     "ADJUSTED PRINCIPAL AMOUNT."

              1.4.    ADDITIONAL INTEREST AMOUNT, PAYMENT AND ADJUSTMENT TO
     INTEREST RATE.

              (a) Upon the achievement by Borrower of EBITDA (calculated in the
     manner set forth in Section 1.4(c) below) greater than $10,000 during any
     complete twelve-month fiscal year prior to the Maturity Date, an Additional
     Interest Amount, as defined below, shall be calculated in respect of the
     outstanding principal amount of this Note for a period (the "ADDITIONAL
     INTEREST COMPUTATION PERIOD") commencing on the Fund Date and ending on the
     Additional Interest Payment Date (defined below). The "ADDITIONAL INTEREST
     AMOUNT" shall be equal to the difference between (i) the aggregate interest
     amount that would have accrued on the outstanding principal amount of this
     Note during the Additional Interest Computation Period at an annual
     interest rate equal to nine percent (9%) based upon a three hundred and
     sixty (360) day year and actual days elapsed, and (ii) the aggregate amount
     of interest due and payable to Lender hereunder (whether or not paid)
     during the same period pursuant to Sections 1.3 (a) and (b) of this Note.
     The Additional Interest Amount shall be paid to Lender in a lump sum on the
     due date (the "ADDITIONAL INTEREST PAYMENT DATE") of the regularly
     scheduled monthly installment due hereunder next following Borrower's
     receipt of Lender's notice of the sum due as the Additional Interest Amount
     (such notice to be delivered no earlier than publication of the applicable
     audited financial statements as part of Borrower's Annual Report on Form
     10-K and no earlier than ten (10) days prior to any such monthly
     installment date), which Additional Interest Amount shall be paid together
     with such regularly scheduled monthly installment.

              (b) Beginning with the Additional Interest Payment Date and
     continuing thereafter for the remainder of the term of this Note, interest
     on the Adjusted Principal Amount shall accrue and be payable in arrears
     hereunder at the greater of (i) nine percent (9%) per annum, or (ii) the
     current Wall Street Journal consensus Prime Rate as such Prime Rate is
     published in THE WALL STREET JOURNAL ("WSJ") based upon a three hundred and
     sixty (360) day year and actual days elapsed. If, as and when such Prime
     Rate changes, the interest rate charged hereunder shall change accordingly
     without any requirement of prior notice to Borrower. In the event that the
     Prime Rate is no longer published by the WSJ, Lender may, in its sole
     discretion reasonably exercised, select any prime rate then published by
     one (1) of the largest ten banks (measured by total assets) in the United
     States. With each change in the interest rate required by this Section 1.4
     (b), the total installment of principal and interest due and payable
     hereunder shall be modified up or down, as the case may be, provided in
     either event the then outstanding Adjusted Principal Amount will fully
     amortize over the balance of the term of this Note.

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              (c) For purposes of this Note, "EBITDA" shall mean for any
     complete twelve-month fiscal year the sum of (i) net income (or loss) of
     Borrower for such period (excluding extraordinary gains and non-cash gains,
     including without limitation any one-time or lump sum license fees and
     development, milestone or similar payments made by any third party as part
     of a strategic partnership or similar arrangement), plus (ii) all interest
     expense of Borrower for such fiscal year, plus (iii) all charges against
     income of Borrower for such fiscal year for federal, state and local taxes,
     plus (iv) depreciation expenses for such fiscal year, plus (v) amortization
     expenses for such period, all determined in accordance with generally
     accepted accounting principles in the United States of America in effect
     from time to time applied on a consistent basis and with reference to the
     Borrower's audited financial statements with respect to such fiscal year.

     2.0.     DEFAULT RATE. To the extent allowed by applicable law, after the
occurrence of any Event of Default and during the continuation thereof (and
after giving effect to any applicable grace or cure periods), after the Maturity
Date, or after judgment has been rendered on this Note, all outstanding
principal and unpaid interest shall bear, until paid, interest at a rate per
annum equal to five (5%) percentage points greater than that which would
otherwise be applicable assessed retroactive to the date that the Event of
Default first occurs (the "DEFAULT RATE").

     3.0.     LATE CHARGE. If a regularly scheduled payment is ten (10) days or
more late, Borrower will be charged five percent (5%) of the unpaid portion of
the regularly scheduled payment or ten dollars ($10.00), whichever is greater.
If Lender demands payment of this Loan after the occurrence and during the
continuation of an Event of Default (after giving effect to any applicable grace
or cure periods), and Borrower does not pay the Loan within fifteen (15) days
after Lender's demand, Borrower will be charged either five percent (5%) of the
unpaid Adjusted Principal Amount plus accrued unpaid interest or ten dollars
($10.00), whichever is greater.

     4.0.     EXPENSES. Borrower further promises to pay to Lender, as incurred,
and as an additional part of the unpaid Adjusted Principal Amount, upon demand
made after the occurrence and during the continuance of an Event of Default all
costs, expenses and reasonable attorneys' fees reasonably incurred by Lender:
(a) in the protection, modification, collection, defense or enforcement of all
or part of this Note or any guaranty hereof; or (b) in the foreclosure or
enforcement of any mortgage or security interest which may now or hereafter
secure the debt hereunder, or (c) with respect to any action taken to protect,
defend, modify or sustain the lien of any such mortgage or security agreement;
or (d) with respect to any litigation or controversy arising from or connected
with this Note or any mortgage or security agreement or collateral which may now
or hereafter secure this Note; or (e) with respect to any act to protect defend,
modify, enforce or release any of its rights or remedies with regard to, or
otherwise effect collection of, any collateral which may now or in the future
secure this Note or with regard to or against Borrower or any endorser,
guarantor or surety of this Note.

     5.0      OPTIONAL PREPAYMENT. Borrower may at any time elect to prepay the
unpaid amount of this Note, or any part thereof, without penalty or premium;
provided, however, that, notwithstanding anything hereinto the contrary, in the
event that any Additional Interest Amount is due and payable pursuant to Section
1.4 hereof, any such prepayment shall first be applied to (i) the Additional
Interest Amount then owed, then to (i) any unpaid Expenses required by Section
4.0 above, then to (iii) Late Fees, if any is due, then to (iv) Default Rate
interest, if any is due, then to (iv) regularly accrued but unpaid interest
pursuant to Section 1.3 above, and then finally to (v) the Adjusted Principal
Amount.

     6.0.     DEFAULT. The happening of any of the following events or
conditions shall constitute an "EVENT OF DEFAULT" under this Note:

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              6.1.    Failure to make any payment of principal or interest on
     any sum due under this Note within five (5) days after the same shall be
     due and payable.

              6.2.    Failure by Borrower to observe or perform any material
     covenant contained herein or a material default or the occurrence of a
     material event of default in any agreement between Borrower and Lender in
     connection herewith, including that certain Leasehold Mortgage and Security
     Agreement by and between Borrower and Lender of even date herewith (the
     "MORTGAGE") beyond the applicable grace or cure period (or, if no such
     grace or cure period is specified, then beyond thirty (30) days following
     the occurrence of any such default or event of default).

              6.3.    Failure by Borrower to observe or perform any material
     covenant contained in that certain Commercial Building Lease by and between
     Borrower and 890 East LLC ("LANDLORD") of even or near date herewith,
     including all addenda and riders thereto (the "LEASE"), or a material
     default or the occurrence of a material event of default under the Lease
     beyond the applicable grace or cure period. A breach of a "material"
     covenant or a "material" default as provided in this Section 6.3 or 6.2
     above mean any breach and/or default of any covenant, term or condition of
     the Lease, this Note, the Mortgage, or other agreement between Borrower and
     Lender which in the Lender's good faith reasonable belief evidences an
     unacceptable decline in the Borrower's ability to fully perform its
     obligations under this Note.

              6.4     Failure of Borrower to exercise its option to extend the
     original term of the Lease for an additional five (5) years pursuant to and
     in accordance with the terms of Section 4 of the Lease, prior the
     expiration of the original term of the Lease.

              6.5.    Any representation or warranty made by Borrower herein or
     in any agreement executed in connection herewith, including the Mortgage,
     or any statement, certificate or other data furnished by Borrower in
     connection herewith or with such agreements, proves at any time to be
     incorrect in any material respect.

              6.6.    A judgment or judgments for the payment of money shall be
     rendered against Borrower in an amount, individually or in the aggregate,
     of at least two hundred fifty thousand dollars ($250,000.00), and any such
     judgment shall remain unsatisfied and in effect for any period of thirty
     (30) consecutive days without a stay of execution, and the Lender holds the
     good faith belief that such unsatisfied judgment or unstayed execution is
     materially adverse to the condition (financial or otherwise) of the
     Borrower or the Lender's collateral for this Note.

              6.7.    Borrower shall: (a) apply for or consent to the
     appointment of a receiver, trustee or liquidator of all or a substantial
     part of any of its assets; (b) admit in writing its inability to pay its
     debts as they mature; (c) file or permit the filing of any petition, case
     arrangement, reorganization, or the like under any insolvency or bankruptcy
     law, or the adjudication of it as a bankrupt, or the making of an
     assignment for the benefit of creditors or the consenting to any form or
     arrangement for the satisfaction, settlement or delay of debt or the
     appointment of a receiver for all or any part of its properties; or (d) any
     action shall be taken by Borrower for the purpose of effecting any of the
     foregoing.

              6.8.    An order, judgment or decree shall be entered, or a case
     shall be commenced, against Borrower, without its application, approval or
     consent by any court of competent jurisdiction, approving a petition or
     permitting the commencement of a case seeking reorganization or liquidation
     of Borrower or appointing a receiver, trustee or liquidator of Borrower, or
     of all or a substantial part of the assets of Borrower, and Borrower, by
     any act,

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     indicates its approval thereof, consent thereto, or acquiescence therein,
     or such order, judgment, decree or case shall continue unstayed and in
     effect for any period of sixty (60) consecutive days, or an order for
     relief in connection therewith shall be entered.

              6.9.    If Borrower shall dissolve or liquidate, or be dissolved
     or liquidated, or cease to legally exist, or merge or consolidate, or be
     merged or consolidated with or into any other corporation or entity.

              6.10.   Failure by Borrower to pay any other indebtedness or
     obligation, or if any such other indebtedness or obligation shall be
     accelerated, or if there exists any event of default under any instrument,
     document or agreement governing, evidencing or securing such other
     indebtedness or obligation, in any event, in an amount, individually or in
     the aggregate, of at least two hundred fifty thousand dollars
     ($250,000.00); and any such amount remains unpaid or any such indebtedness
     or obligations remain accelerated or any such event of default remains
     uncured, in each case, for any period of thirty (30) consecutive days; and
     the Lender holds the good faith belief that such unpaid indebtedness or
     event of default is materially adverse to the condition (financial or
     otherwise) of the Borrower or the Lender's collateral for this Note.

              Upon and after an Event of Default, the whole of said
indebtedness, both principal and interest, and including any other sums which
may become due under this Note, shall, at the option of the holder of this Note,
immediately become due and payable without presentment, demand, protest, notice
of protest, or other notice of dishonor of any kind, all of which are hereby
expressly waived by Borrower.

     7.0.     MAXIMUM PERMISSIBLE INTEREST RATE. Borrower shall not be obligated
to pay and Lender shall not collect interest at a rate higher than the maximum
permitted by law or the maximum that will not subject Lender to any civil or
criminal penalties. If, because of the acceleration of maturity the payment of
interest in advance or any other reason, Borrower is required, under the
provisions hereof, pursuant to the provisions of any other agreements,
instruments, documents, security agreements, mortgages, financing statements,
and supplements thereto and relating to the Loan, or entered into between
Borrower in favor of, or with, Lender, at any time, for any purpose (the "LOAN
DOCUMENTS") or otherwise, to pay interest at a rate in excess of such maximum
rate, the rate of interest under such provisions shall immediately and
automatically be reduced to such maximum rate and any payment made in excess of
such maximum rate shall be applied to principal outstanding hereunder or, if
received by applicable law, shall be returned to Borrower.

     8.0.     [RESERVED].

     9.0.     REPLACEMENT DOCUMENTS. Upon receipt of an affidavit of an officer
of Lender as to the loss, theft, destruction or mutilation of the Note or any
other security document(s), together with an agreement reasonably satisfactory
to the Borrower to indemnify the Borrower from any loss incurred by it in
connection therewith, and, in the case of any such loss, theft, destruction or
mutilation, upon surrender and cancellation of such Note or other document(s),
Borrower will issue, in lieu thereof, a replacement Note or other document(s) in
the same principal amount thereof and otherwise of like tenor.

     10.0     COMMITMENT LETTER. This Note contains the entire understanding of
the parties with respect to the matters contained herein and supercedes all
prior understandings and writings related thereto (including without limitation
that certain Commitment Letter executed by Lender and Borrower and dated May 12,
2004, which is superceded by this Note).

     11.0.    CONSENT TO JURISDICTION. Borrower hereby agrees that any state or
local court of the Commonwealth of Massachusetts or any United States District
Court for the District of Massachusetts or,

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at the option of Lender, any court in which Lender shall initiate legal or
equitable proceedings and which has subject matter jurisdiction over the matter
in controversy, shall have exclusive jurisdiction to hear and determine any
claims or disputes between Borrower and Lender pertaining directly or indirectly
to this Note or to any matter arising in connection with this Note.

     12.0.    WAIVERS. Borrower agrees that no delay or failure on the part of
the holder in exercising any power, privilege, remedy, option or right hereunder
shall operate as a waiver thereof or of any other power, privilege, remedy or
right; nor shall any single or partial exercise of any power, privilege, remedy,
option or right hereunder preclude any other or future exercise thereof or the
exercise of any other power, privilege, remedy, option or right. The rights and
remedies expressed herein are cumulative, and may be enforced successively,
alternately, or concurrently and are not exclusive of any rights or remedies
which holder may or would otherwise have under the provisions of all applicable
laws, and under the provisions of all agreements between Borrower and Lender.

     Borrower hereby waives presentment, demand, notice, protest and all other
demands and notices in connection with the delivery, acceptance, performance,
default or enforcement of this Note. Borrower hereby assents to any extension or
postponement of the time of payment or any other indulgence, to the addition or
release of any party or person primarily or secondarily liable, and to the
addition, release and/or substitution of all or any portion of any collateral
now or hereafter securing this Note.

     BORROWER AND LENDER MUTUALLY HEREBY KNOWINGLY, VOLUNTARILY AND
INTENTIONALLY WAIVE THE RIGHT TO A TRIAL BY JURY IN RESPECT OF ANY CLAIM BASED
HEREON, ARISING OUT OF, UNDER OR IN CONNECTION WITH THIS NOTE OR ANY OTHER
DOCUMENTS CONTEMPLATED TO BE EXECUTED IN CONNECTION HEREWITH OR ANY COURSE OF
CONDUCT, COURSE OF DEALING, STATEMENTS (WHETHER ORAL OR WRITTEN) OR ACTIONS OF
ANY PARTY. THIS WAIVER CONSTITUTES A MATERIAL INDUCEMENT FOR LENDER TO MAKE THE
LOAN AND ACCEPT THIS NOTE.

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     This Note is executed as a sealed instrument and shall be governed by and
construed in accordance with the laws of the Commonwealth of Massachusetts.

WITNESS:                                  BORROWER:

                                          ACUSPHERE, INC.

/s/ John F. Thero                         By: /s/ Sherri C. Oberg
-----------------------------------          -----------------------------------
    John F. Thero                         Name: Sherri C. Oberg
                                                Title: President and CEO
                                                Duly Authorized

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                                                                 Exhibit 10.34

                            MASTER SECURITY AGREEMENT
                dated as of April 16, 2004 ("AGREEMENT")

     THIS AGREEMENT is between GENERAL ELECTRIC CAPITAL CORPORATION (together
with its successors and assigns, if any, "SECURED PARTY") and ACUSPHERE, INC.
("DEBTOR"). Secured Party has an office at 401 Merritt 7 Suite 23, Norwalk, CT
06851-1177. Debtor is a corporation organized and existing under the laws of the
state of Delaware ("the State"). Debtor's mailing address and chief place of
business is 500 Arsenal Street, Watertown, MA 02472.

1.   CREATION OF SECURITY INTEREST.

     Debtor grants to Secured Party a security interest in and against all
property listed on any collateral schedule now or in the future annexed to or
made a part of this Agreement ("COLLATERAL SCHEDULE"), and in and against all
additions, attachments, accessories and accessions to such property, all
substitutions, replacements or exchanges therefor, and all insurance and/or
other proceeds thereof (all such property is individually and collectively
called the "COLLATERAL"). This security interest is given to secure the payment
and performance of all debts, obligations and liabilities of any kind whatsoever
of Debtor to Secured Party, now existing or arising in the future, including but
not limited to the payment and performance of certain Promissory Notes from time
to time identified on any Collateral Schedule (collectively "NOTES" and each a
"NOTE"), and any renewals, extensions and modifications of such debts,
obligations and liabilities (such Notes, debts, obligations and liabilities are
called the "INDEBTEDNESS").

2.   REPRESENTATIONS, WARRANTIES AND COVENANTS OF DEBTOR.

     Debtor represents, warrants and covenants as of the date of this Agreement
and as of the date of each Collateral Schedule that:

     (a) Debtor's exact legal name is as set forth in the preamble of this
Agreement and Debtor is, and will remain, duly organized, existing and in good
standing under the laws of the State set forth in the preamble of this
Agreement, has its chief executive offices at the location specified in the
preamble, and is, and will remain, duly qualified and licensed in every
jurisdiction wherever necessary to carry on its business and operations;

     (b) Debtor has adequate power and capacity to enter into, and to perform
its obligations under this Agreement, each Note and any other documents
evidencing, or given in connection with, any of the Indebtedness (all of the
foregoing are called the "DEBT DOCUMENTS");

     (c) This Agreement and the other Debt Documents have been duly authorized,
executed and delivered by Debtor and constitute legal, valid and binding
agreements enforceable in accordance with their terms, except to the extent that
the enforcement of remedies may be limited under applicable bankruptcy and
insolvency laws;

     (d) No approval, consent or withholding of objections is required from any
governmental authority or instrumentality with respect to the entry into, or
performance by Debtor of any of the Debt Documents, except any already obtained;

     (e) The entry into, and performance by, Debtor of the Debt Documents will
not (i) violate any of the organizational documents of Debtor or any judgment,
order, law or regulation applicable to Debtor, or (ii) result in any breach of
or constitute a default under any contract to which Debtor is a party, or result
in the creation of any lien, claim or encumbrance on any of Debtor's property
(except for liens in favor of Secured Party) pursuant to any indenture,
mortgage, deed of trust, bank loan, credit agreement, or other agreement or
instrument to which Debtor is a party;

     (f) There are no suits or proceedings pending in court or before any
commission, board or other administrative agency against or affecting Debtor
which could, in the aggregate, have a material adverse effect on Debtor, its
business or operations, or its ability to perform its obligations under the Debt
Documents, nor does Debtor have reason to believe that any such suits or
proceedings are threatened;

     (g) All financial statements delivered to Secured Party in connection with
the Indebtedness have been prepared in accordance with generally accepted
accounting principles, provided that those financial statements that are
unaudited are subject to normal year-end adjustments, which adjustments Debtor
does not

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expect to be material, and do not contain all footnotes required under generally
accepted accounting principles, and since the date of the most recent financial
statement, there has been no material adverse change in Debtors financial
condition;

     (h) The Collateral is not, and will not be, used by Debtor for personal,
family or household purposes;

     (i) The Collateral is, and will remain, in good condition and repair and
Debtor will not be negligent in its care and use;

     (j) Debtor is, and will remain, the sole and lawful owner, and in
possession of, the Collateral, and has the sole right and lawful authority to
grant the security interest described in this Agreement;

     (k) The Collateral is, and will remain, free and clear of all liens, claims
and encumbrances of any kind whatsoever, except for (i) liens in favor of
Secured Party, (ii) liens for taxes or other governmental charges not yet due or
for taxes or other governmental charges being contested in good faith and which
do not involve, in the reasonable judgment of Secured Party, the imminent risk
of the sale, forfeiture or loss of any material portion of the Collateral, and
(iii) inchoate materialmen's, mechanic's, repairmen's and similar liens and
liens to secure payment of workers' compensation, employment insurance, or other
social security obligations of Debtor in the ordinary course of business arising
by operation of law in the normal course of business for amounts which are not
delinquent (all of such liens are called "PERMITTED LIENS"); and

     (l) Debtor is and will remain in full compliance with all laws and
regulations applicable to it including, without limitation, (i) if required,
ensuring that no person who owns a controlling interest in or otherwise controls
Debtor is or shall be (Y) listed on the Specially Designated Nationals and
Blocked Person List maintained by the Office of Foreign Assets Control ("OFAC"),
Department of the Treasury, and/or any other similar lists maintained by OFAC
pursuant to any authorizing statute, Executive Order or regulation or (Z) a
person designated under Section 1(b), (c) or (d) of Executive Order No. 13224
(September 23, 2001), any related enabling legislation or any other similar
Executive Orders, and (ii) compliance with all applicable Bank Secrecy Act
("BSA") laws, regulations and government guidance on BSA compliance and on the
prevention and detection of money laundering violations.

3.   COLLATERAL.

     (a) Until the declaration of any default, Debtor shall remain in possession
of the Collateral; except that Secured Party shall have the right to possess (i)
any chattel paper or instrument that constitutes a part of the Collateral, and
(ii) any other Collateral in which Secured Party's security interest may be
perfected only by possession. Secured Party may inspect any of the Collateral
during normal business hours after giving Debtor reasonable prior notice. If
Secured Party asks, Debtor will promptly notify Secured Party in writing of the
location of any Collateral.

     (b) Debtor shall (i) use the Collateral only in its trade or business, (ii)
maintain all of the Collateral in good operating order and repair, normal wear
and tear excepted, (iii) use and maintain the Collateral only in compliance with
manufacturers recommendations and all applicable laws, and (iv) keep all of the
Collateral free and clear of all liens, claims and encumbrances (except for
Permitted Liens).

     (c) Secured Party does not authorize and Debtor agrees it shall not (i)
part with possession of any of the Collateral (except to Secured Party or for
maintenance and repair), (ii) remove any of the Collateral from the continental
United States, or (iii) sell, rent, lease, mortgage, license, grant a security
interest in or otherwise transfer or encumber (except for Permitted Liens) any
of the Collateral.

     (d) Debtor shall pay promptly when due all taxes, license fees, assessments
and public and private charges levied or assessed on any of the Collateral, on
its use, or on this Agreement or any of the other Debt Documents. At its option,
Secured Party may discharge taxes, liens, security interests or other
encumbrances at any time levied or placed on the Collateral and may pay for the
maintenance, insurance and preservation of the Collateral and effect compliance
with the terms of this Agreement or any of the other Debt Documents. Debtor
agrees to reimburse Secured Party, on demand, all costs and expenses incurred by
Secured Party in connection with such payment or performance and agrees that
such reimbursement obligation shall constitute Indebtedness.

     (e) Debtor shall, at all times, keep accurate and complete records of the
Collateral, and Secured Party shall have the right to inspect and make copies of
all of Debtor's books and records relating to the Collateral during normal
business hours, after giving Debtor reasonable prior notice.

     (f) Debtor agrees and acknowledges that any third person who may at any
time possess all or any portion of the Collateral shall be deemed to hold, and
shall hold, the Collateral as the agent of, and as pledge holder for, Secured
Party. Secured Party may at any time give notice to any third person described
in the preceding sentence that such third person is holding the Collateral as
the agent of, and as pledge holder for, the Secured Party. Notwithstanding the
foregoing, Debtor may place Collateral with a third party contract manufacturer
provided that all parties enter into a mutually acceptable Tri-Party Agreement.

<Page>

4.   INSURANCE.

     (a) Debtor shall at all times bear the entire risk of any loss, theft,
damage to, or destruction of, any of the Collateral from any cause whatsoever.

     (b) Debtor agrees to keep the Collateral insured against loss or damage by
fire and extended coverage perils, theft, burglary, and for any or all
Collateral which are vehicles, for risk of loss by collision, and if requested
by Secured Party, against such other risks as Secured Party may reasonably
require. The insurance coverage shall be in an amount no less than the full
replacement value of the Collateral, and deductible amounts, insurers and
policies shall be acceptable to Secured Party. Debtor shall deliver to Secured
Party policies or certificates of insurance evidencing such coverage. Each
policy shall name Secured Party as a loss payee, shall provide for coverage to
Secured Party regardless of the breach by Debtor of any warranty or
representation made therein, shall not be subject to co-insurance, and shall
provide that coverage may not be canceled or altered by the insurer except upon
thirty (30) days prior written notice to Secured Party. Debtor appoints Secured
Party as its attorney-in-fact to make proof of loss, claim for insurance and
adjustments with insurers, and to receive payment of and execute or endorse all
documents, checks or drafts in connection with insurance payments. Secured Party
shall not act as Debtor's attorney-in-fact unless Debtor is in default. Proceeds
of insurance shall be applied, at the option of Secured Party, to repair or
replace the Collateral or to reduce any of the Indebtedness.

5.   REPORTS.

     (a) Debtor shall promptly notify Secured Party of (i) any change in the
name of Debtor, (ii) any change in the state of its incorporation, organization
or registration, (iii) any relocation of its chief executive offices, (iv) any
relocation of any material portion of the Collateral, (v) any material portion
of the Collateral being lost, stolen, missing, destroyed, materially damaged or
worn out, or (vi) any lien, claim or encumbrance other than Permitted Liens
attaching to or being made against any material portion of the Collateral.

     (b) Debtor will deliver to Secured Party financial statements as follows.
If Debtor is a privately held company, then Debtor agrees to provide monthly
financial statements, certified by Debtor's president or chief financial officer
including a balance sheet, statement of operations and cash flow statement
within 30 days of each month end and its complete audited annual financial
statements, certified by a recognized firm of certified public accountants,
within 120 days of fiscal year end or at such time as Debtor's Board of
Directors receives the audit. If Debtor is a publicly held company, then Debtor
agrees to provide quarterly unaudited statements and annual audited statements,
audited by a recognized firm of certified public accountants, within 10 days
after the statements are provided to the Securities and Exchange Commission
("SEC"). All such statements are to be prepared using generally accepted
accounting principles ("GAAP") provided that those financial statements that are
unaudited are subject to normal year-end adjustments, which adjustments Debtor
does not expect to be material, and do not contain all footnotes required under
generally accepted accounting principles, and, if Debtor is a publicly held
company, are to be in compliance with SEC requirements.

6.   FURTHER ASSURANCES.

     (a) Debtor shall, upon request of Secured Party, furnish to Secured Party
such further information, execute and deliver to Secured Party such documents
and instruments (including, without limitation, Uniform Commercial Code
financing statements) and shall do such other acts and things as Secured Party
may at any time reasonably request relating to the perfection or protection of
the security interest created by this Agreement or for the purpose of carrying
out the intent of this Agreement. Without limiting the foregoing, Debtor shall
cooperate and do all acts deemed necessary or advisable by Secured Party to
continue in Secured Party a perfected first security interest in the Collateral,
and shall obtain and furnish to Secured Party any subordinations, releases,
landlord waivers, lessor waivers, mortgagee waivers, or control agreements, and
similar documents as may be from time to time reasonably requested by, and in
form and substance satisfactory to, Secured Party.

     (b) Debtor authorizes Secured Party to file a financing statement and
amendments thereto describing the Collateral and containing any other
information required by the applicable Uniform Commercial Code. Debtor shall, if
any certificate of title be required or permitted by law for any of the
Collateral, obtain and promptly deliver to Secured Party such certificate
showing the lien of this Agreement with respect to the Collateral. Debtor
ratifies its prior authorization for Secured Party to file financing statements
and amendments thereto describing the Collateral and containing any other
information required by the Uniform Commercial Code if filed prior to the date
hereof.

     (c) Debtor shall indemnify and defend the Secured Party, its successors and
assigns, and their respective directors, officers and employees, from and
against all third party claims, actions and suits (including, without
limitation, related attorneys' fees) of any kind whatsoever arising, directly or
indirectly, in

<Page>

connection with any of the Collateral provided that such claim, action or suit
does not arise out of Secured Party's bad faith, willful misconduct, gross
negligence or breach of the Agreement.

7.   DEFAULT AND REMEDIES.

     (a) Debtor shall be in default under this Agreement and each of the other
Debt Documents if:

         (i)     Debtor breaches its obligation to pay when due any installment
or other amount due or coming due under any of the Debt Documents and fails to
cure the breach within ten (10) days;

         (ii)    Debtor, without the prior written consent of Secured Party,
attempts to or does sell, rent, lease, license, mortgage, grant a security
interest in, or otherwise transfer or encumber (except for Permitted Liens) any
of the Collateral;

         (iii)   Debtor breaches any of its insurance obligations under
Section 4;

         (iv)    Debtor breaches any of its other obligations under any of the
Debt Documents and fails to cure that breach within thirty (30) days after
written notice from Secured Party;

         (v)     Any warranty, representation or statement made by Debtor in any
of the Debt Documents or otherwise in connection with any of the Indebtedness
shall be false or misleading in any material respect when made;

         (vi)    Any material portion of the Collateral is subjected to
attachment, execution, levy, seizure or confiscation in any legal proceeding or
otherwise, or if any legal or administrative proceeding is commenced against
Debtor or any material portion of the Collateral, which in the good faith
judgment of Secured Party subjects any material portion of the Collateral to a
material risk of attachment, execution, levy, seizure or confiscation and no
bond is posted or protective order obtained to negate such risk;

         (vii)   Debtor breaches or is in default under any other agreement
between Debtor and Secured Party;

         (viii)  Debtor or any guarantor or other obligor for any of the
Indebtedness (collectively "GUARANTOR") dissolves, terminates its existence,
becomes insolvent or ceases to do business as a going concern;

         (ix)    If Debtor or any Guarantor is a natural person, Debtor or any
such Guarantor dies or becomes incompetent;

         (x)     A receiver is appointed for all or of any part of the property
of Debtor or any Guarantor, or Debtor or any Guarantor makes any assignment for
the benefit of creditors;

         (xi)    Debtor or any Guarantor files a petition under any bankruptcy,
insolvency or similar law, or any such petition is filed against Debtor or any
Guarantor and is not dismissed within sixty (60) days;

         (xii)   Debtor's improper and unauthorized filing of an amendment or
termination statement relating to a filed financing statement describing the
Collateral;

         (xiii)  There is a material adverse change in the Debtor's financial
condition as determined solely by Secured Party. Secured Party understands that
Debtor anticipates reporting continued losses and this alone shall not be
construed as a material adverse change. In addition, Secured Party understands
that Debtor anticipates the need to incur additional indebtedness. Such
additional indebtedness shall not be construed as a material adverse change in
and of itself so long as such debt is on commercially reasonable terms.

         (xiv)   Any Guarantor revokes or attempts to revoke its guaranty of any
of the Indebtedness or fails to observe or perform any covenant, condition or
agreement to be performed under any guaranty or other related document to which
it is a party;

         (xv)    Debtor is in default under any other material obligation for
(A) borrowed money, (B) the deferred purchase price of property or (C) payments
due under any lease agreement; or

<Page>

         (xvi) At any time during the term of this Agreement Debtor sells more
than 50% of its interest in the company to another corporation or business or
all or substantially all of its assets without Secured Party's prior written
consent, which such consent shall not be unreasonably withheld.

     (b) If Debtor is in default, the Secured Party, at its option, may declare
any or all of the Indebtedness to be immediately due and payable, without demand
or notice to Debtor or any Guarantor. The accelerated obligations and
liabilities shall bear interest (both before and after any judgment) until paid
in full at the lower of eighteen percent (18%) per annum or the maximum rate not
prohibited by applicable law.

     (c) During default, Secured Party shall have all of the rights and remedies
of a Secured Party under the Uniform Commercial Code, and under any other
applicable law. Without limiting the foregoing, Secured Party shall have the
right during Debtor's default to (i) notify any account debtor of Debtor or any
obligor on any instrument which constitutes part of the Collateral to make
payment to the Secured Party, (ii) with or without legal process, peaceably
enter any premises where the Collateral may be and take possession of and remove
the Collateral from the premises or store it on the premises, (iii) sell the
Collateral at public or private sale, in whole or in part, and have the right to
bid and purchase at said sale, or (iv) lease or otherwise dispose of all or part
of the Collateral, applying proceeds from such disposition to the obligations
then in default. If requested by Secured Party, Debtor shall promptly assemble
the Collateral and make it available to Secured Party at a place to be
designated by Secured Party which is reasonably convenient to both parties.
Secured Party may also render any or all of the Collateral unusable at the
Debtor's premises and may dispose of such Collateral on such premises without
liability for rent or costs. Any notice that Secured Party is required to give
to Debtor under the Uniform Commercial Code of the time and place of any public
sale or the time after which any private sale or other intended disposition of
the Collateral is to be made shall be deemed to constitute reasonable notice if
such notice is given to the last known address of Debtor at least ten (10) days
prior to such action.

     (d) Proceeds from any sale or lease or other disposition shall be applied:
first, to all costs of repossession, storage, and disposition including without
limitation attorneys', appraisers', and auctioneers' fees; second, to discharge
the obligations then in default; third, to discharge any other Indebtedness of
Debtor to Secured Party, whether as obligor, endorser, guarantor, surety or
indemnitor; fourth, to expenses incurred in paying or settling liens and claims
against the Collateral; and lastly, to Debtor, if there exists any surplus.
Debtor shall remain fully liable for any deficiency.

     (e) Debtor agrees to pay all reasonable attorneys' fees and other costs
incurred by Secured Party in connection with the enforcement, assertion, defense
or preservation of Secured Party's rights and remedies under this Agreement, or
if prohibited by law, such lesser sum as may be permitted. Debtor further agrees
that such fees and costs shall constitute Indebtedness.

     (f) Secured Party's rights and remedies under this Agreement or otherwise
arising are cumulative and may be exercised singularly or concurrently. Neither
the failure nor any delay on the part of the Secured Party to exercise any
right, power or privilege under this Agreement shall operate as a waiver, nor
shall any single or partial exercise of any right, power or privilege preclude
any other or further exercise of that or any other right, power or privilege.
SECURED PARTY SHALL NOT BE DEEMED TO HAVE WAIVED ANY OF ITS RIGHTS UNDER THIS
AGREEMENT OR UNDER ANY OTHER AGREEMENT, INSTRUMENT OR PAPER SIGNED BY DEBTOR
UNLESS SUCH WAIVER IS EXPRESSED IN WRITING AND SIGNED BY SECURED PARTY. A waiver
on any one occasion shall not be construed as a bar to or waiver of any right or
remedy on any future occasion.

     (g) DEBTOR AND SECURED PARTY UNCONDITIONALLY WAIVE THEIR RIGHTS TO A JURY
TRIAL OF ANY CLAIM OR CAUSE OF ACTION BASED UPON OR ARISING OUT OF THIS
AGREEMENT, ANY OF THE OTHER DEBT DOCUMENTS, ANY OF THE INDEBTEDNESS SECURED
HEREBY, ANY DEALINGS BETWEEN DEBTOR AND SECURED PARTY RELATING TO THE SUBJECT
MATTER OF THIS TRANSACTION OR ANY RELATED TRANSACTIONS, AND/OR THE RELATIONSHIP
THAT IS BEING ESTABLISHED BETWEEN DEBTOR AND SECURED PARTY. THE SCOPE OF THIS
WAIVER IS INTENDED TO BE ALL ENCOMPASSING OF ANY AND ALL DISPUTES THAT MAY BE
FILED IN ANY COURT. THIS WAIVER IS IRREVOCABLE. THIS WAIVER MAY NOT BE MODIFIED
EITHER ORALLY OR IN WRITING. THE WAIVER ALSO SHALL APPLY TO ANY SUBSEQUENT
AMENDMENTS, RENEWALS, SUPPLEMENTS OR MODIFICATIONS TO THIS AGREEMENT, ANY OTHER
DEBT DOCUMENTS, OR TO ANY OTHER DOCUMENTS OR AGREEMENTS RELATING TO THIS
TRANSACTION OR ANY RELATED TRANSACTION. THIS AGREEMENT MAY BE FILED AS A WRITTEN
CONSENT TO A TRIAL BY THE COURT.

8.   MISCELLANEOUS.

     (a) This Agreement, any Note and/or any of the other Debt Documents may be
assigned, in whole or in part, by Secured Party without notice to Debtor. Debtor
agrees that if Debtor receives written notice of an assignment from Secured
Party, Debtor will pay all amounts payable under any assigned Debt Documents to
such assignee or as instructed by Secured Party. Until Debtor receives written
notice of such assignment, Debtor may pay all amounts payable under the Debt
Documents to the Secured Party, who shall be solely responsible for forwarding
such payments to the assignee. Debtor also agrees to confirm in writing receipt
of the notice of assignment as may be reasonably requested by Secured Party or
assignee.

<Page>

     (b) All notices to be given in connection with this Agreement shall be in
writing, shall be addressed to the parties at their respective addresses set
forth in this Agreement (unless and until a different address may be specified
in a written notice to the other party), and shall be deemed given (i) on the
date of receipt if delivered in hand or by facsimile transmission, (ii) on the
next business day after being sent by express mail or overnight carrier, and
(iii) on the fourth business day after being sent by regular, registered or
certified mail. As used herein, the term "business day" shall mean and include
any day other than Saturdays, Sundays, or other days on which commercial banks
in New York, New York are required or authorized to be closed.

     (c) Secured Party may correct patent errors and fill in all blanks in this
Agreement or in any Collateral Schedule consistent with the written agreement of
the parties.

     (d) Time is of the essence of this Agreement. This Agreement shall be
binding, jointly and severally, upon all parties described as the "Debtor" and
their respective heirs, executors, representatives, successors and assigns, and
shall inure to the benefit of Secured Party, its successors and assigns.

     (e) This Agreement and its Collateral Schedules constitute the entire
agreement between the parties with respect to the subject matter of this
Agreement and supersede all prior understandings (whether written, verbal or
implied) with respect to such subject matter. THIS AGREEMENT AND ITS COLLATERAL
SCHEDULES SHALL NOT BE CHANGED OR TERMINATED ORALLY OR BY COURSE OF CONDUCT, BUT
ONLY BY A WRITING SIGNED BY BOTH PARTIES. Section headings contained in this
Agreement have been included for convenience only, and shall not affect the
construction or interpretation of this Agreement.

     (f) This Agreement shall continue in full force and effect until all of the
Indebtedness has been indefeasibly paid in full to Secured Party or its
assignee. The surrender, upon payment or otherwise, of any Note or any of the
other documents evidencing any of the Indebtedness shall not affect the right of
Secured Party to retain the Collateral for such other Indebtedness as may then
exist or as it may be reasonably contemplated will exist in the future. This
Agreement shall automatically be reinstated if Secured Party is ever required to
return or restore the payment of all or any portion of the Indebtedness (all as
though such payment had never been made).

     (g) Debtor authorizes Secured Party to use its name, logo and/or trademark
without notice to or consent by Debtor, in connection with certain promotional
materials that Secured Party may disseminate to the public. The promotional
materials may include, but are not limited to, brochures, video tape, internet
website, press releases, advertising in newspaper and/or other periodicals,
lucites, and any other materials relating the fact that Secured Party has a
financing relationship with Debtor and such materials may be developed,
disseminated and used without Debtor's review. Nothing herein obligates Secured
Party to use Debtor's name, logo and/or trademark, in any promotional materials
of Secured Party.

     (h) THIS AGREEMENT AND THE RIGHTS AND OBLIGATIONS OF THE PARTIES HEREUNDER
SHALL IN ALL RESPECTS BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH, THE
INTERNAL LAWS OF THE STATE OF CONNECTICUT (WITHOUT REGARD TO THE CONFLICT OF
LAWS PRINCIPLES OF SUCH STATE), INCLUDING ALL MATTERS OF CONSTRUCTION, VALIDITY
AND PERFORMANCE, REGARDLESS OF THE LOCATION OF THE COLLATERAL.

          IN WITNESS WHEREOF, Debtor and Secured Party, intending to be legally
  bound hereby, have duly executed this Agreement in one or more counterparts,
  each of which shall be deemed to be an original, as of the day and year first
  aforesaid.

  SECURED PARTY:                                   DEBTOR:

  GENERAL ELECTRIC CAPITAL CORPORATION             ACUSPHERE, INC.

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

  Name: John Edel                           Name: Sherri C. Oberg
       --------------------------------          -------------------------------

  Title: SVP                                Title: President and CEO
        -------------------------------           ------------------------------

<Page>

                          EQUIPMENT CONCENTRATION RIDER

ACUSPHERE, INC. ("Customer"), on or before February 28, 2005 shall cause the
composition and mix of Equipment financed after April 16, 2004 under the
Master Security Agreement dated as of April 16, 2004 between Customer and
General Electric Capital Corporation to conform to and meet the following
concentration requirements (hereinafter "Concentration Requirements") for
each class of Equipment (hereinafter "Equipment Class") as identified and set
forth below. Customer herein represents and warrants that it shall maintain
each such Equipment Class and its respective Concentration Requirement from
and after such above referenced date and continuing thereafter to the end of
the term:

<Table>
<Caption>
     EQUIPMENT CLASS                            CONCENTRATION REQUIREMENT
     ---------------                            -------------------------
     <S>                                        <C>
     New Lab, Lab Support, Scientific
      and Manufacturing Equipment               Minimum of 70%

     New Computer Hardware, Software,
      Tenant Improvements and General
      Office Equipment                          Maximum of 30%
</Table>

Accepted and Agreed:

ACUSPHERE, INC.

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

Title: President and CEO
       -------------------------------

Date:
        -------------------------------

<Page>

                  COLLATERAL SCHEDULE NO. ____________________

THIS COLLATERAL SCHEDULE NO. ____________________ is annexed to and made a part
of that certain Master Security Agreement dated as of __________________________
between General Electric Capital Corporation, together with its successors and
assigns, if any, as Secured Party and Acusphere, Inc. as Debtor and describes
collateral in which Debtor has granted Secured Party a security interest in
connection with the Indebtedness (as defined in the Security Agreement)
including without limitation that certain Promissory Note dated
____________________ in the original principal amount of $____________________.

<Table>
<Caption>
QUANTITY     MANUFACTURER       SERIAL NUMBER       YEAR/MODEL AND TYPE OF EQUIPMENT
--------     ------------       -------------       --------------------------------
<S>          <C>                <C>                 <C>
</Table>

SEE EXHIBIT A ATTACHED HERETO AND MADE A PART HEREOF

and including all additions, attachments, accessories and accessions thereto,
and any and all substitutions, replacements or exchanges therefor, and all
insurance and/or other proceeds thereof.

 SECURED PARTY:                          DEBTOR:

 GENERAL ELECTRIC CAPITAL CORPORATION    ACUSPHERE, INC.

 By:                                      By:
    ---------------------------------        -----------------------------------

 Name:                                    Name:
      -------------------------------          ---------------------------------

 Title:                                   Title:
       ------------------------------           --------------------------------

 Date:                                    Date:
      -------------------------------          ---------------------------------

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