Document:

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                                                                   Exhibit 10.01

                                 ACUSPHERE, INC.
                                 1994 STOCK PLAN

     1.   PURPOSE. The purpose of the Acusphere, Inc. 1994 Stock Plan (the
"Plan") is to encourage key employees of Acusphere, Inc. (the "Company") and of
any present or future parent or subsidiary of the Company (collectively,
"Related Corporations") and other individuals who render services to the
Company, by providing opportunities to participate in the ownership of the
Company and its future growth through (a) the grant of options which qualify as
"incentive stock options" ("ISOs") under Section 422(b) of the Internal Revenue
Code of 1986, as amended (the "Code"); (b) the grant of options which do not
qualify as ISOs ("Non-Qualified Options"); (c) awards of stock in the Company
("Awards"); and (d) opportunities to make direct purchases of stock in the
Company ("Purchases"). Both ISOs and Non-Qualified Options are referred to
hereafter individually as an "Option" and collectively as "Options." Options,
Awards and authorizations to make Purchases are referred to hereafter
collectively as "Stock Rights." As used herein, the terms "parent" and
"subsidiary" mean "parent corporation" and "subsidiary corporation,"
respectively, as those terms are defined in Section 424 of the Code.

     2.   ADMINISTRATION OF THE PLAN.

          A.   BOARD OR COMMITTEE ADMINISTRATION. The Plan shall be administered
     by the Board of Directors of the Company (the "Board") or by a committee
     appointed by the Board (the "Committee"); provided that the Plan shall be
     administered to the extent required by Rule 16b-3 promulgated under the
     Securities Exchange Act of 1934 or any successor provision ("Rule 16b-3"),
     by a disinterested administrator or administrators within the meaning of
     Rule 16b-3. Hereinafter, all references in this Plan to the "Committee"
     shall mean the Board if no Committee has been appointed. Subject to
     ratification of the grant or authorization of each Stock Right by the Board
     (if so required by applicable state law), and subject to the terms of the
     Plan, the Committee shall have the authority to (i) determine to whom (from
     among the class of employees eligible under paragraph 3 to receive ISOs)
     ISOs shall be granted, and to whom (from among the class of individuals and
     entities eligible under paragraph 3 to receive Non-Qualified Options and
     Awards and to make Purchases) Non-Qualified Options, Awards and
     authorizations to make Purchases may be granted; (ii) determine the time or
     times at which Options or Awards shall be granted or Purchases made; (iii)
     determine the purchase price of shares subject to each Option or Purchase,
     which prices shall not be less than the minimum price specified in
     paragraph 6; (iv) determine whether each Option granted shall be an ISO or
     a Non-Qualified Option; (v) determine (subject to paragraph 7) the time or
     times when each Option shall become exercisable and the duration of the
     exercise period; (vi) determine whether restrictions such as repurchase
     options are to be imposed on shares subject to Options, Awards and
     Purchases and the nature of such restrictions, if any, and (vii) interpret
     the Plan and prescribe and rescind rules and regulations relating to it. If
     the Committee determines to issue a Non-Qualified Option, it shall take
     whatever actions it deems necessary, under Section 422 of the Code and the

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     regulations promulgated thereunder, to ensure that such Option is not
     treated as an ISO. The interpretation and construction by the Committee of
     any provisions of the Plan or of any Stock Right granted under it shall be
     final unless otherwise determined by the Board. The Committee may from time
     to time adopt such rules and regulations for carrying out the Plan as it
     may deem advisable. No member of the Board or the Committee shall be liable
     for any action or determination made in good faith with respect to the Plan
     or any Stock Right granted under it.

          B.   COMMITTEE ACTIONS. The Committee may select one of its members as
     its chairman, and shall hold meetings at such time and places as it may
     determine. A majority of the Committee shall constitute a quorum and acts
     of a majority of the members of the Committee at a meeting at which a
     quorum is present, or acts reduced to or approved in writing by all the
     members of the Committee, shall be the valid acts of the Committee. From
     time to time the Board may increase the size of the Committee and appoint
     additional members thereof, remove members (with or without cause) and
     appoint new members in substitution therefor, fill vacancies however
     caused, or remove all members of the Committee and thereafter directly
     administer the Plan.

          C.   GRANT OF STOCK RIGHTS TO BOARD MEMBERS. Subject to the provisions
     of the first sentence of paragraph 2(A) above, if applicable, Stock Rights
     may be granted to members of the Board. All grants of Stock Rights to
     members of the Board shall in all other respects be made in accordance with
     the provisions of this Plan applicable to other eligible persons. Members
     of the Board who either (i) are eligible to receive grants of Stock Rights
     pursuant to the Plan or (ii) have been granted Stock Rights may vote on any
     matters affecting the administration of the Plan or the grant of any Stock
     Rights pursuant to the Plan, except that no such member shall act upon the
     granting to himself of Stock Rights, but any such member may be counted in
     determining the existence of a quorum at any meeting of the Board during
     which action is taken with respect to the granting to such member of Stock
     Rights.

     3.   ELIGIBLE EMPLOYEES AND OTHERS. ISOs may be granted only to employees
of the Company or any Related Corporation. Non-Qualified Options, Awards and
authorizations to make Purchases may be granted to any employee, officer or
director (whether or not also an employee) or consultant of the Company or any
Related Corporation. The Committee may take into consideration a recipient's
individual circumstances in determining whether to grant a Stock Right. The
granting of any Stock Right to any individual or entity shall neither entitle
that individual or entity to, nor disqualify him from, participation in any
other grant of Stock Rights.

     4.   STOCK. The stock subject to Stock Rights shall be authorized but
unissued shares of Common Stock of the Company, par value $.01 per share (the
"Common Stock"), or shares of Common Stock reacquired by the Company in any
manner. The aggregate number of shares which may be issued pursuant to the Plan
is 1,385,458, subject to adjustment as provided in paragraph 13. If any Stock
Right granted under the Plan shall expire or terminate for any reason without
having been exercised in full or shall cease for any reason to be exercisable in
whole or

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in part, the unpurchased shares subject to such Stock Right shall again be
available for grants of Stock Rights under the Plan.

     5.   GRANTING OF STOCK RIGHTS. Stock Rights may be granted under the Plan
at any time after March 7, 1994 and prior to March 7, 2004. The date of grant of
a Stock Right under the Plan will be the date specified by the Committee at the
time it grants the Stock Right; provided, however, that such date shall not be
prior to the date on which the Committee acts to approve the grant.

     6.   MINIMUM OPTION PRICE; ISO LIMITATIONS.

          A.   PRICE FOR NON-QUALIFIED OPTIONS, AWARDS AND PURCHASES. The
     exercise price per share specified in the agreement relating to each
     Non-Qualified Option granted, and the purchase price per share of stock
     granted in any Award or authorized as a Purchase, under the Plan shall in
     no event be less than the minimum legal consideration required therefor
     under the laws of Delaware or the laws of any jurisdiction in which the
     Company or its successors in interest may be organized.

          B.   PRICE FOR ISOS. The exercise price per share specified in the
     agreement relating to each ISO granted under the Plan shall not be less
     than the fair market value per share of Common Stock on the date of such
     grant. In the case of an ISO to be granted to an employee owning stock
     possessing more than ten percent (10%) of the total combined voting power
     of all classes of stock of the Company or any Related Corporation, the
     price per share specified in the agreement relating to such ISO shall not
     be less than one hundred ten percent (110%) of the fair market value per
     share of Common Stock on the date of grant. For purposes of determining
     stock ownership under this paragraph, the rules of Section 424(d) of the
     Code shall apply.

          C.   $100,000 ANNUAL LIMITATION ON ISO VESTING. Each eligible employee
     may be granted Options treated as ISOs only to the extent that, in the
     aggregate under this Plan and all incentive stock option plans of the
     Company and any Related Corporation, ISOs do not become exercisable for the
     first time by such employee during any calendar year with respect to stock
     having a fair market value (determined at the time the ISOs were granted)
     in excess of $100,000. The Company intends to designate any Options granted
     in excess of such limitation as Non-Qualified Options.

          D.   DETERMINATION OF FAIR MARKET VALUE. If, at the time an Option is
     granted under the Plan, the Company's Common Stock is publicly traded,
     "fair market value" shall be determined as of the last business day for
     which the prices or quotes discussed in this sentence are available prior
     to the date such Option is granted and shall mean (i) the average (on that
     date) of the high and low prices of the Common Stock on the principal
     national securities exchange on which the Common Stock is traded, if the
     Common Stock is then traded on a national securities exchange; or (ii) the
     last reported sale price (on that date) of the Common Stock on the Nasdaq
     National Market, if the Common Stock is not then traded on a national
     securities exchange; or (iii) the closing bid price (or average of bid
     prices) last

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     quoted (on that date) by an established quotation service for
     over-the-counter securities, if the Common Stock is not reported on the
     Nasdaq National Market. If the Common Stock is not publicly traded at the
     time an Option is granted under the Plan, "fair market value" shall mean
     the fair value of the Common Stock as determined by the Committee after
     taking into consideration all factors which it deems appropriate,
     including, without limitation, recent sale and offer prices of the Common
     Stock in private transactions negotiated at arm's length.

     7.   OPTION DURATION. Subject to earlier termination as provided in
paragraphs 9 and 10 or in the agreement relating to such Option, each Option
shall expire on the date specified by the Committee, but not more than (i) ten
years from the date of grant in the case of Options generally and (ii) five
years from the date of grant in the case of ISOs granted to an employee owning
stock possessing more than ten percent (10%) of the total combined voting power
of all classes of stock of the Company or any Related Corporation, as determined
under paragraph 6(B). Subject to earlier termination as provided in paragraphs 9
and 10, the term of each ISO shall be the term set forth in the original
instrument granting such ISO, except with respect to any part of such ISO that
is converted into a Non-Qualified Option pursuant to paragraph 16.

     8.   EXERCISE OF OPTION. Subject to the provisions of paragraphs 9 through
12, each Option granted under the Plan shall be exercisable as follows:

          A.   VESTING. The Option shall either be fully exercisable on the date
     of grant or shall become exercisable thereafter in such installments as the
     Committee may specify.

          B.   FULL VESTING OF INSTALLMENTS. Once an installment becomes
     exercisable it shall remain exercisable until expiration or termination of
     the Option, unless otherwise specified by the Committee.

          C.   PARTIAL EXERCISE. Each Option or installment may be exercised at
     any time or from time to time, in whole or in part, for up to the total
     number of shares with respect to which it is then exercisable.

          D.   ACCELERATION OF VESTING. The Committee shall have the right to
     accelerate the date that any installment of any Option becomes exercisable;
     provided that the Committee shall not, without the consent of an optionee,
     accelerate the permitted exercise date of any installment of any Option
     granted to any employee as an ISO (and not previously converted into a
     Non-Qualified Option pursuant to paragraph 16) if such acceleration would
     violate the annual vesting limitation contained in Section 422(d) of the
     Code, as described in paragraph 6(C).

     9.   TERMINATION OF EMPLOYMENT. Unless otherwise specified in the agreement
relating to such ISO, if an ISO optionee ceases to be employed by the Company
and all Related Corporations other than by reason of death or disability as
defined in paragraph 10, no further installments of his or her ISOs shall become
exercisable, and his or her ISOs shall terminate on the earlier of (a) ninety
(90) days after the date of termination of his or her employment, or (b)

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their specified expiration dates, except to the extent that such ISOs (or
unexercised installments thereof) have been converted into Non-Qualified Options
pursuant to paragraph 16. For purposes of this paragraph 9, employment shall be
considered as continuing uninterrupted during any bona fide leave of absence
(such as those attributable to illness, military obligations or governmental
service) provided that the period of such leave does not exceed 90 days or, if
longer, any period during which such optionee's right to reemployment is
guaranteed by statute. A bona fide leave of absence with the written approval of
the Committee shall not be considered an interruption of employment under this
paragraph 9, provided that such written approval contractually obligates the
Company or any Related Corporation to continue the employment of the optionee
after the approved period of absence. ISOs granted under the Plan shall not be
affected by any change of employment within or among the Company and Related
Corporations, so long as the optionee continues to be an employee of the Company
or any Related Corporation. Nothing in the Plan shall be deemed to give any
grantee of any Stock Right the right to be retained in employment or other
service by the Company or any Related Corporation for any period of time.

     10.  DEATH; DISABILITY.

          A.   DEATH. If an ISO optionee ceases to be employed by the Company
     and all Related Corporations by reason of his or her death, any ISO owned
     by such optionee may be exercised, to the extent otherwise exercisable on
     the date of his death, by his estate, personal representative or
     beneficiary who has acquired the ISO by will or by the laws of descent and
     distribution, until the earlier of (i) the specified expiration date of the
     ISO or (ii) 180 days from the date of the optionee's death.

          B.   DISABILITY. If an ISO optionee ceases to be employed by the
     Company and all Related Corporations by reason of his or her disability,
     such optionee shall have the right to exercise any ISO held by him or her
     on the date of termination of employment, for the number of shares for
     which he or she could have exercised it on that date, until the earlier of
     the specified expiration date of the ISO or or 180 days from the date of
     the termination of the optionee's employment. For the purposes of the Plan,
     the term "disability" shall mean "permanent and total disability" as
     defined in Section 22(e)(3) of the Code or any successor statute.

     11.  ASSIGNABILITY. No Stock Right shall be assignable or transferable by
the grantee except by will, by the laws of descent and distribution or, in the
case of Non-Qualified Options only, pursuant to a valid domestic relations
order. Except as set forth in the previous sentence, during the lifetime of a
grantee each Stock Right shall be exercisable only by such grantee.

     12.  TERMS AND CONDITIONS OF OPTIONS. Options shall be evidenced by
instruments (which need not be identical) in such forms as the Committee may
from time to time approve. Such instruments shall conform to the terms and
conditions set forth in paragraphs 6 through 11 hereof and may contain such
other provisions as the Committee deems advisable which are not inconsistent
with the Plan, including restrictions applicable to shares of Common Stock
issuable upon exercise of Options. The Committee may specify that any
Non-Qualified Option shall be

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subject to the restrictions set forth herein with respect to ISOs, or to such
other termination and cancellation provisions as the Committee may determine.
The Committee may from time to time confer authority and responsibility on one
or more of its own members and/or one or more officers of the Company to execute
and deliver such instruments. The proper officers of the Company are authorized
and directed to take any and all action necessary or advisable from time to time
to carry out the terms of such instruments.

     13.  ADJUSTMENTS. Upon the occurrence of any of the following events, an
optionee's rights with respect to Options granted to such optionee hereunder
shall be adjusted as hereinafter provided, unless otherwise specifically
provided in the written agreement between the optionee and the Company relating
to such Option:

          A.   STOCK DIVIDENDS AND STOCK SPLITS. If the shares of Common Stock
     shall be subdivided or combined into a greater or smaller number of shares
     or if the Company shall issue any shares of Common Stock as a stock
     dividend on its outstanding Common Stock, the number of shares of Common
     Stock deliverable upon the exercise of Options shall be appropriately
     increased or decreased proportionately, and appropriate adjustments shall
     be made in the purchase price per share to reflect such subdivision,
     combination or stock dividend.

          B.   CONSOLIDATIONS OR MERGERS. If the Company is to be consolidated
     with or acquired by another entity in a merger, sale of all or
     substantially all of the Company's assets or otherwise (an "Acquisition"),
     the Committee or the board of directors of any entity assuming the
     obligations of the Company hereunder (the "Successor Board"), shall, as to
     outstanding Options, either (i) make appropriate provision for the
     continuation of such Options by substituting on an equitable basis for the
     shares then subject to such Options either (a) the consideration payable
     with respect to the outstanding shares of Common Stock in connection with
     the Acquisition, (b) shares of stock of the surviving corporation or (c)
     such other securities as the Successor Board deems appropriate, the fair
     market value of which shall not materially exceed the fair market value of
     the shares of Common Stock subject to such Options immediately preceding
     the Acquisition; or (ii) upon written notice to the optionees, provide that
     all Options must be exercised, to the extent then exercisable, within a
     specified number of days of the date of such notice, at the end of which
     period the Options shall terminate; or (iii) terminate all Options in
     exchange for a cash payment equal to the excess of the fair market value of
     the shares subject to such Options (to the extent then exercisable) over
     the exercise price thereof.

          C.   RECAPITALIZATION OR REORGANIZATION. In the event of a
     recapitalization or reorganization of the Company (other than in connection
     with a transaction described in subparagraph B above) pursuant to which
     securities of the Company or of another corporation are issued with respect
     to the outstanding shares of Common Stock, an optionee upon exercising an
     Option shall be entitled to receive for the purchase price paid upon such
     exercise the securities he would have received if he had exercised his
     Option prior to such recapitalization or reorganization.

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          D.   MODIFICATION OF ISOS. Notwithstanding the foregoing, any
     adjustments made pursuant to subparagraphs A, B or C with respect to ISOs
     shall be made only after the Committee, after consulting with counsel for
     the Company, determines whether such adjustments would constitute a
     "modification" of such ISOs (as that term is defined in Section 424 of the
     Code) or would cause any adverse tax consequences for the holders of such
     ISOs. If the Committee determines that such adjustments made with respect
     to ISOs would constitute a modification of such ISOs or would cause adverse
     tax consequences to the holders, it may refrain from making such
     adjustments.

          E.   DISSOLUTION OR LIQUIDATION. In the event of the proposed
     dissolution or liquidation of the Company, each Option will terminate
     immediately prior to the consummation of such proposed action or at such
     other time and subject to such other conditions as shall be determined by
     the Committee.

          F.   ISSUANCES OF SECURITIES. Except as expressly provided herein, no
     issuance by the Company of shares of stock of any class, or securities
     convertible into shares of stock of any class, shall affect, and no
     adjustment by reason thereof shall be made with respect to, the number or
     price of shares subject to Options. No adjustments shall be made for
     dividends paid in cash or in property other than securities of the Company.

          G.   FRACTIONAL SHARES. No fractional shares shall be issued under the
     Plan and the optionee shall receive from the Company cash in lieu of such
     fractional shares.

          H.   ADJUSTMENTS. Upon the happening of any of the events described in
     subparagraphs A, B or C above, the class and aggregate number of shares set
     forth in paragraph 4 hereof that are subject to Stock Rights which
     previously have been or subsequently may be granted under the Plan shall
     also be appropriately adjusted to reflect the events described in such
     subparagraphs. The Committee or the Successor Board shall determine the
     specific adjustments to be made under this paragraph 13 and, subject to
     paragraph 2, its determination shall be conclusive.

     14.  MEANS OF EXERCISING OPTIONS. An option (or any part or installment
thereof) shall be exercised by giving written notice to the Company at its
principal office address, or to such transfer agent as the Company shall
designate. Such notice shall identify the Option being exercised and specify the
number of shares as to which such Option is being exercised, accompanied by full
payment of the purchase price therefor either (a) in United States dollars in
cash or by check, (b) at the discretion of the Committee, through delivery of
shares of Common Stock having a fair market value equal as of the date of the
exercise to the cash exercise price of the Option, (c) at the discretion of the
Committee, by delivery of the grantee's personal recourse note bearing interest
payable not less than annually at no less than 100% of the lowest applicable
Federal rate, as defined in Section 1274(d) of the Code, (d) at the discretion
of the Committee and consistent with applicable law, through the delivery of an
assignment to the Company of a sufficient amount of the proceeds from the sale
of the Common Stock acquired upon exercise of the Option and an authorization to
the broker or selling agent to pay that amount to the Company, which sale shall
be at the participant's direction at the time of exercise, or (e) at the
discretion of

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the Committee, by any combination of (a), (b), (c) and (d) above. If the
Committee exercises its discretion to permit payment of the exercise price of an
ISO by means of the methods set forth in clauses (b), (c), (d) or (e) of the
preceding sentence, such discretion shall be exercised in writing at the time of
the grant of the ISO in question. The holder of an Option shall not have the
rights of a shareholder with respect to the shares covered by such Option until
the date of issuance of a stock certificate to such holder for such shares.
Except as expressly provided above in paragraph 13 with respect to changes in
capitalization and stock dividends, no adjustment shall be made for dividends or
similar rights for which the record date is before the date such stock
certificate is issued.

     15.  TERM AND AMENDMENT OF PLAN. This Plan was adopted by the Board on
March 7, 1994, subject, with respect to the validation of ISOs granted under the
Plan, to approval of the Plan by the stockholders of the Company at the next
Meeting of Stockholders or, in lieu thereof, by written consent. If the approval
of stockholders is not obtained prior to March 7, 1995, any grants of ISOs under
the Plan made prior to that date will be rescinded. The Plan shall expire at the
end of the day on March 7, 2004 (except as to Options outstanding on that date).
Subject to the provisions of paragraph 5 above, Options may be granted under the
Plan prior to the date of stockholder approval of the Plan. The Board may
terminate or amend the Plan in any respect at any time, except that, without the
approval of the stockholders obtained within 12 months before or after the Board
adopts a resolution authorizing any of the following actions: (a) the total
number of shares that may be issued under the Plan may not be increased (except
by adjustment pursuant to paragraph 13); (b) the benefits accruing to
participants under the Plan may not be materially increased; (c) the
requirements as to eligibility for participation in the Plan may not be
materially modified; (d) the provisions of paragraph 3 regarding eligibility for
grants of ISOs may not be modified; (e) the provisions of paragraph 6(B)
regarding the exercise price at which shares may be offered pursuant to ISOs may
not be modified (except by adjustment pursuant to paragraph 13); (f) the
expiration date of the Plan may not be extended; and (g) the Board may not take
any action which would cause the Plan to fail to comply with Rule 16b-3. Except
as otherwise provided in this paragraph 15, in no event may action of the Board
or stockholders alter or impair the rights of a grantee, without such grantee's
consent, under any Option previously granted to such grantee.

     16.  CONVERSION OF ISOS INTO NON-QUALIFIED OPTIONS. The Committee, at the
written request or with the written consent of any optionee, may in its
discretion take such actions as may be necessary to convert such optionee's ISOs
(or any installments or portions of installments thereof) that have not been
exercised on the date of conversion into Non-Qualified Options at any time prior
to the expiration of such ISOs, regardless of whether the optionee is an
employee of the Company or a Related Corporation at the time of such conversion.
Such actions may include, but shall not be limited to, extending the exercise
period or reducing the exercise price of the appropriate installments of such
ISOs. At the time of such conversion, the Committee (with the consent of the
optionee) may impose such conditions on the exercise of the resulting
Non-Qualified Options as the Committee in its discretion may determine, provided
that such conditions shall not be inconsistent with this Plan. Nothing in the
Plan shall be deemed to give any optionee the right to have such optionee's ISOs
converted into Non-Qualified Options, and no such conversion shall occur until
and unless the Committee takes appropriate action.

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     17.  APPLICATION OF FUNDS. The proceeds received by the Company from the
sale of shares pursuant to Options granted and Purchases authorized under the
Plan shall be used for general corporate purposes.

     18.  NOTICE TO COMPANY OF DISQUALIFYING DISPOSITION. By accepting an ISO
granted under the Plan, each optionee agrees to notify the Company in writing
immediately after he makes a Disqualifying Disposition (as described in Sections
421, 422 and 424 of the Code and regulations thereunder) of any stock acquired
pursuant to the exercise of ISOs granted under the Plan. A Disqualifying
Disposition is generally any disposition occurring on or before the later of (a)
the date two years following the date the ISO was granted or (b) the date one
year following the date the ISO was exercised.

     19.  WITHHOLDING OF ADDITIONAL INCOME TAXES. Upon the exercise of a
Non-Qualified Option, the grant of an Award, the making of a Purchase of Common
Stock for less than its fair market value, the making of a Disqualifying
Disposition (as defined in paragraph 18), the vesting or transfer of restricted
stock or securities acquired on the exercise of an Option hereunder, or the
making of a distribution or other payment with respect to such stock or
securities, the Company may withhold taxes in respect of amounts that constitute
compensation includible in gross income. The Committee in its discretion may
condition (i) the exercise of an Option, (ii) the grant of an Award, (iii) the
making of a Purchase of Common Stock for less than its fair market value, or
(iv) the vesting or transferability of restricted stock or securities acquired
by exercising an Option, on the grantee's making satisfactory arrangement for
such withholding. Such arrangement may include payment by the grantee in cash or
by check of the amount of the withholding taxes or, at the discretion of the
Committee, by the grantee's delivery of previously held shares of Common Stock
or the withholding from the shares of Common Stock otherwise deliverable upon
exercise of a Option shares having an aggregate fair market value equal to the
amount of such withholding taxes.

     20.  GOVERNMENTAL REGULATION. The Company's obligation to sell and deliver
shares of the Common Stock under this Plan is subject to the approval of any
governmental authority required in connection with the authorization, issuance
or sale of such shares.

     Government regulations may impose reporting or other obligations on the
Company with respect to the Plan. For example, the Company may be required to
send tax information statements to employees and former employees that exercise
ISOs under the Plan, and the Company may be required to file tax information
returns reporting the income received by grantees of Options in connection with
the Plan.

     21.  GOVERNING LAW. The validity and construction of the Plan and the
instruments evidencing Options shall be governed by the laws of Delaware, or the
laws of any jurisdiction in which the Company or its successors in interest may
be organized.
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                  REGISTER OF AMENDMENTS TO THE 1994 STOCK PLAN

March 29, 1995 by Written Consent of the Stockholders:

Section 4 was amended to increase the number of authorized shares from 573,528
to 532,359 shares.

March 26, 1996 by Written Consent of the Stockholders:

Section 4 was amended to increase the number of authorized shares from 532,359
to 568,520 shares.

May 30, 1996 by Written Consent of the Stockholders:

Section 4 was amended to increase the number of authorized shares from 568,520
to 851,346 shares.

August 21, 1997 by Written Consent of the Stockholders:

Section 4 was amended to increase the number of authorized shares from 851,346
to 1,385,458 shares.

March 30, 1999 by Written Consent of the Stockholders:

Section 4 was amended to increase the number of authorized shares from 1,385,458
to 1,985,458 shares.

March 1, 2001 by Written Consent of the Stockholders:

Section 4 was amended to increase the number of authorized shares from 1,985,458
to 3,985,458 shares.

June 14, 2001, by Written Consent of the Stockholders:

Section 4 was amended to increase the number of authorized shares from 3,985,458
to 6,051,977 shares.

April 11, 2003, by Written Consent of the Stockholders:

Section 4 was amended to increase the number of authorized shares from 6,051,977
to 6,591,977 shares.<PAGE>

                                                                   Exhibit 10.04

                              AMENDED AND RESTATED

                            STOCKHOLDERS' AGREEMENT

     THIS AGREEMENT, made as of the 24th day of January, 1994, by and among
Polymers for Medicine, Inc., a Delaware corporation (the "Company"), and Robert
S. Langer ("Langer"), Sherri C. Oberg ("Oberg"), Harry R. Allcock ("Allcock"),
Walter Levison ("Levison") and Richard L. Kronenthal ("Kronenthal")
(collectively, the "Stockholders" and individually, a "Stockholder"), amends and
restates the Stockholders' Agreement, dated October 29, 1993, as amended by
Amendment No. 1, dated November 18, 1993 (the "Original Agreement") by and among
the Company, Langer, Oberg, Allcock and Levison.

     WHEREAS, pursuant to the Original Agreement, Langer, Oberg, Allcock and
Levison made provision for certain arrangements regarding the outstanding stock
of the Company held by them;

     WHEREAS, Kronenthal has acquired shares of the Company's Common Stock, and
the Stockholders and the Company desire that such shares be covered by
restrictions and other arrangements similar to those contained in the Original
Agreement; and

     WHEREAS, the Langer, Oberg, Allcock, Levison and the Company desire to
amend and restate the Original Agreement in its entirety as set forth in this
Agreement.

     NOW, THEREFORE, in consideration of the mutual promises hereinafter set
forth and of other good and valuable consideration, the receipt and sufficiency
of which is hereby acknowledged, the parties hereto, intending to be legally
bound, hereby agree as follows:

     1.   CERTAIN DEFINED TERMS. As used in this Agreement, the following terms
shall have the following respective meanings:

          (a) "Stock" shall mean and include all shares of Common Stock and all
other securities of the Company which may be issued in exchange for or in
respect of shares of Common Stock (whether by way of stock split, stock
dividend, combination, reclassification, reorganization, or any other means).

          (b) "Shares" shall mean and include all shares of Stock now owned or
hereafter acquired by any Stockholder. For purposes of this Agreement, all of
the Stock which a Stockholder has a right to acquire from the Company upon the
conversion, exercise or exchange of any of the securities of the Company then
owned by such Stockholder shall be deemed to be Shares then owned by such
Stockholder.

<PAGE>

                                     - 2 -

          (c) "Vesting Shares" shall mean the shares of Common Stock held by
each Stockholder on the date hereof and any Shares acquired in the future in
respect of such Shares by reason of any stock split, stock dividend,
recombination or similar event.

          (d) "Unvested Shares" shall mean Vesting Shares which have not yet
become Vested Shares under paragraph (e) below.

          (e) "Vested Shares" shall mean, as to each Stockholder, the following
percentages of the Vesting Shares held by such Stockholder on the following
dates:

With respect to each Stockholder other than Kronenthal:

On or after the date          --     2.08%
hereof but prior to                  for each complete
July 1, 1997                         month during which the
                                     Stockholder is employed
                                     by, a consultant to, or
                                     a director of the
                                     Company after July 1,
                                     1993; and

On or after July 1, 1997      --     100%; and

With respect to Kronenthal:

On or after the date          --     2.08%
hereof but prior to                  for each complete
February 1, 1998                     month during which the
                                     Stockholder (or a
                                     corporation wholly-owned by
                                     him) is employed by,
                                     a consultant to, or
                                     a director of the
                                     Company after the date
                                     hereof; and

On or after February 1, 1998  --     100%.

;PROVIDED HOWEVER, that no additional Vesting Shares shall become Vested Shares
after the date upon which such Stockholder ceases to be employed by, a
consultant to or a director of the Company or any of its subsidiaries except as
provided in Section 5(a); and, FURTHER PROVIDED, that if, while any of a
Stockholder's shares remain Unvested Shares, (i) there occurs (A) a sale of all
or substantially all of the Company's assets, or (B) a consolidation, merger,
tender offer or sale of outstanding stock in each case in which there is a
change in control of at least 51% of the Company's outstanding capital stock (an
"Acquisition"), whether such Acquisition takes place as the result of a single
transaction or group of related transactions with a single acquiror or with more
than one related acquirors, and (ii) within one year of the date of the
Acquisition (or last

<PAGE>

                                     - 3 -

transaction in the case of a related group of transactions which together shall
constitute an Acquisition) the employment, consulting or directorship of such
Stockholder with the Company is terminated other than as a result of the
voluntary action of such Stockholder or the death or disability of such
Stockholder, then all Unvested Shares held by such Stockholder shall immediately
become fully vested as of the date upon which such employment, consulting or
directorship shall cease.

     2.   PROHIBITED TRANSFERS. No Stockholder shall sell, assign, transfer,
pledge, hypothecate, mortgage, encumber or dispose of all or any of his Shares
except to the Company or as expressly provided in this Agreement.
Notwithstanding the foregoing, a Stockholder may transfer all or any of his
Shares (other than Unvested Shares) (i) by way of gift to any member of his
family or to any trust for the benefit of any such family member or such
Stockholder, provided that any such transferee shall agree in writing with the
Company, as a condition to such transfer, to be bound by all of the provisions
of this Agreement to the same extent as if such transferee were the Stockholder,
or (ii) by will or the laws of descent and distribution, in which event each
such transferee shall be bound by all of the provisions of this Agreement to the
same extent as if such transferee were the Stockholder. As used herein, the word
"family" shall include any spouse, lineal ancestor or descendant, brother or
sister.

     3.   RIGHT OF FIRST REFUSAL ON DISPOSITIONS.

          (a) If at any time any Stockholder desires to sell for cash or cash
equivalents all or any portion of his Shares (other than Unvested Shares)
pursuant to a bona fide offer from a third party (the "Proposed Transferee"),
such selling Stockholder shall submit a written offer (the "Offer") to sell such
Shares (the "Offered Shares") to the Company and the other Stockholders on terms
and conditions, including price, not less favorable to the Company and the other
Stockholders than those on which the selling Stockholder proposes to sell such
Offered Shares to the Proposed Transferee. The Offer shall disclose the identity
of the Proposed Transferee, the Offered Shares proposed to be sold, the total
number of Shares (other than Unvested Shares) owned by the selling Stockholder,
the terms and conditions, including price, of the proposed sale, and any other
material facts relating to the proposed sale. The Offer shall further state that
the Company and the other Stockholders may acquire, in accordance with the
provisions of this Agreement, all or any portion of the Offered Shares for the
price and upon the other terms and conditions, including deferred payment (if
applicable), set forth therein. The Company may assign its right to purchase the
Offered Shares by delivering written notice to the selling Stockholder.

<PAGE>

                                     - 4 -

          (b) If the Company elects not to purchase all or any portion of the
Offered Shares (the Offered Shares not purchased by the Company are hereinafter
referred to as the "Remaining Offered Shares"), each other Stockholder shall
have the absolute right to purchase that number of Remaining Offered Shares as
shall be equal to the number of Remaining Offered Shares multiplied by a
fraction, the numerator of which shall be the number of Shares then owned by
such participating other Stockholder and the denominator of which shall be the
aggregate number of Shares then owned by all of the participating other
Stockholders. (The amount of Remaining Offered Shares that each participating
other Stockholder is entitled to purchase under this Section 3(b) shall be
referred to as its "Pro Rata Fraction" ).

          (c) The participating other Stockholders shall have a right of
oversubscription such that if any participating other Stockholder fails to
accept the Offer as to its Pro Rata Fraction, the participating other
Stockholders shall, among them, have the right to purchase up to the balance of
the Remaining Offered Shares not so purchased. Such right of oversubscription
may be exercised by a participating other Stockholder by accepting the Offer as
to more than its Pro Rata Fraction. If, as a result thereof, such
oversubscriptions exceed the total number of Remaining Offered Shares available
in respect of such oversubscription privilege, the oversubscribing participating
other Stockholders shall be cut back with respect to their oversubscriptions on
a pro rata basis in accordance with their respective Pro Rata Fractions or as
they may otherwise agree among themselves.

          (d) If the Company or any other Stockholder desires to purchase all or
any portion of the Offered Shares, the Company, its assignee or said other
Stockholder shall communicate in writing its election to purchase to the selling
Stockholder, which communication shall state the number of Offered Shares the
Company, its assignee or said participating other Stockholder desires to
purchase and shall be delivered in person or mailed to the selling Stockholder
at the address set forth in accordance with Section 10 below within ten days of
the date the Offer was made. Such communication shall, when taken in conjunction
with the Offer, be deemed to constitute a valid, legally binding and enforceable
agreement for the sale and purchase of such Offered Shares. Sales of the Offered
Shares to be sold to the Company or participating other Stockholders pursuant to
this Section 3 shall be made at the offices of the Company on the 20th day
following the date the Offer was made (or if such 20th day is not a business
day, then on the next succeeding business day). Such sales shall be effected by
the selling Stockholder's delivery to the Company or participating other
Stockholder of a certificate or certificates evidencing the Offered Shares to be
purchased by it, duly endorsed for transfer to the Company or participating

<PAGE>

                                     - 5 -

other Stockholder, as the case may be, against payment to the selling
Stockholder of the purchase price therefor by the Company or said participating
other Stockholder, as the case may be.

          (e) If the Company and the other Stockholders do not purchase all of
the Offered Shares, the Offered Shares not so purchased may be sold by the
selling Stockholder at any' time within 45 days after the date the Offer was
made to the Company and the other Stockholders, subject to the provisions of
Sections 4 and 5. Any such sale shall be to the Proposed Transferee, at not less
than the price and upon other terms and conditions, if any, not more favorable
to the Proposed Transferee than those specified in the Offer. Any Offered Shares
not sold within such 45-day period shall continue to be subject to the
requirements of a prior offer pursuant to this Section 3. If Offered Shares are
sold pursuant to this Section 3 to any purchaser who is not a party to this
Agreement, the Offered Shares so sold shall no longer be subject to any of the
restrictions imposed by this Agreement and shall no longer be entitled to any of
the benefits conferred by this Agreement

          (f) The Stockholders' right of refusal provided in this Section 3
shall not apply with respect to sales of Shares to the Company.

     4.   RIGHT OF PARTICIPATION IN SALES.

          (a) If at any time a Stockholder desires to sell all or any portion of
the Shares (other than Unvested Shares) owned by him to any person or entity
(the "Purchaser"), each of the other Stockholders shall have the right to sell
to the Purchaser, as a condition to such sale by the selling Stockholder, at the
same price per share and on the same terms and Conditions as involved in such
sale by the selling Stockholder, the same percentage of the Shares (other than
Unvested Shares) owned by such other Stockholder as the Shares (other than
Unvested Shares) to be sold by the selling Stockholder to the Purchaser
represents with respect to the Shares (other than Unvested Shares) owned by the
selling Stockholder immediately prior to the sale of any of his Shares (other
than Unvested Shares) to the Purchaser.

          (b) Each other Stockholder wishing to so participate in any sale under
this Section 4 shall notify the selling Stockholder in writing of such intention
as soon as practicable after such other Stockholder's receipt of the Offer
pursuant to Section 3, and in any event within ten days after the date the Offer
was made. "Such notification shall be delivered in person or mailed to the
selling Stockholder at the address set forth in accordance with Section 10
below.

          (c) The selling Stockholder and each participating other Stockholder
shall sell to the Purchaser all, or at the option of the Purchaser, any portion
of the Shares proposed to be

<PAGE>

                                     - 6 -

sold by them at not less than the price and upon other terms and conditions, if
any, not more favorable to the Purchaser than those in the Offer provided by the
selling Stockholder under Section 3 above; PROVIDED, HOWEVER, that any purchase
of less than all of such Shares by the Purchaser shall be made from the selling
Stockholder and each participating other Stockholder pro rata based upon the
relative amount of the Shares (other than Unvested Shares) that the selling
Stockholder and each participating other Stockholder is otherwise entitled to
sell pursuant to Section 4(a).

          (d) If Shares are sold pursuant to this Section 4 to any purchaser who
is not a party to this Agreement, the Shares so sold shall no longer be subject
to any of the restrictions imposed by this Agreement and shall no longer be
entitled to any of the benefits conferred by this Agreement.

          (e) The right to participate in sales provided by this Section 4 shall
not apply with respect to sales of Shares (a) to the Company or (b) other
Stockholders pursuant to Section 3.

     5.   OPTION OF COMPANY UPON. TERMINATION OF EMPLOYMENT, ETC.

          (a) If a Stockholder shall for any reason, including, without
limitation, death, disability or involuntary removal with or without cause,
cease to be employed in any capacity by, a consultant to or a director of the
Company or any of its subsidiaries, the Company may within 120 days from the
date upon which such relationships shall cease exercise its option under this
Section 5 to purchase from such Stockholder all of his Unvested Shares. In the
event a Stockholder ceases to be employed by reason of death or disability, 50%
of any Unvested Shares on the date of termination shall become Vested Shares for
purposes of this Section 5.

          (b) The purchase price of any Unvested Shares for which the Company
exercises its option under this Section 5 (the "Option Price") shall be $.01 per
share of Common Stock (such price being subject to equitable adjustment for any
stock split, stock dividend, combination of shares or the like and based upon
Common Stock or Common Stock equivalents).

          (c) If the Company desires to exercise its option to purchase, it
shall do so by communicating in writing its election to purchase to the
Stockholder, which communication shall state the number of Unvested Shares the
Company is electing to purchase and the Option Price and shall be delivered in
person or mailed to the Stockholder at the address set forth in accordance with
Section 10 below within the 120-day period provided for in pursuant to this
Section 5 shall be made at the offices of the Company on the 20th day following
the date of the Company's written election to purchase (or if such 20th day is
not a

<PAGE>

                                     - 7 -

business day, then on the next succeeding business day). Such sale shall be
effected by the Stockholder's delivery to the Company of a certificate or
certificates evidencing the Shares to be purchased by it, duly endorsed for
transfer to the Company, against payment to the Stockholder by the Company of
the applicable Option Price for each Share to be purchased by the Company.

          (d) In addition to the other restrictions provided in this Agreement,
in no event shall a Stockholder transfer any Shares pursuant to any other
Section of this Agreement if, upon completing such transfer, such Stockholder
would be unable to meet his obligations (whether accrued or contingent) under
this Section 5.

     6.   TERM. Sections 3 and 4 of this Agreement shall terminate (a)
immediately prior to the consummation of the first firm commitment underwritten
public offering pursuant to an effective registration statement on Form S-1 (or
its then equivalent) under the Securities Act of 1933, as amended, pursuant to
which the net proceeds to the Company from the sale of the Stock is at least
$7,500,000 or (b) on the tenth anniversary of the date of this Agreement,
whichever occurs first. This Agreement shall terminate on the tenth anniversary
of the date of this Agreement.

     7.   FAILURE TO DELIVER SHARES. If any party hereto becomes obligated to
sell any Shares to another party under this Agreement and fails to deliver such
Shares in accordance with the terms of this Agreement, such other party may, at
its option, in addition to all other remedies it may have, send to such
defaulting party the purchase price for such Shares as is herein specified.
Thereupon, the Company upon written notice to such defaulting party, (a) shall
cancel on its books the certificate or certificates representing the Shares to
be sold and (b) shall issue, in lieu thereof, in the name of such other party, a
new certificate or certificates representing such Shares, and thereupon all of
the rights of the former holder in and to such Shares shall terminate.

     8.   SPECIFIC ENFORCEMENT. Each party hereto expressly agrees that the
other parties hereto will be irreparably damaged if this Agreement is not
specifically enforced. Upon a breach or threatened breach of the terms,
covenants and/or conditions of this Agreement by a party, any other party shall,
in addition to all other remedies, each be entitled to a temporary or permanent
injunction, without showing any actual damage, and/or a decree for specific
performance, in accordance with the provisions hereof.

     9.   LEGEND. Each certificate evidencing any of the Shares shall bear a
legend substantially as follows:

<PAGE>

                                     - 8 -

          "The shares represented by this certificate are subject to
          restrictions on transfer and may not be sold, exchanged, transferred,
          pledged, hypothecated or other- wise disposed of except in accordance
          with and subject to all the terms and conditions of a certain Amended
          and Restated Stockholders' Agreement dated as of January ,1994, a
          copy of which the Company will furnish to the holder of this
          certificate upon request and without charge."

     10.  NOTICES. Notices given hereunder shall be deemed to have been duly
given on the date of personal delivery or on the date of postmark if mailed by
certified or registered mail, return receipt requested, to the party being
notified at his or its address specified on the applicable signature page hereto
or such other address as the addressee may subsequently notify the other parties
of in writing.

     11.  ENTIRE AGREEMENT AND AMENDMENTS. The Company, Langer, Oberg, Allcock
and Levison agree that this Agreement amends and restates the Original Agreement
in its entirety and that the Original Agreement is hereby terminated and of no
further force or effect. This Agreement constitutes the entire agreement of the
parties with respect to the subject matter hereof and neither this Agreement nor
any provision hereof may be waived, modified, amended or terminated except by a
written agreement signed by the parties hereto; PROVIDED, HOWEVER, that
Stockholders owning at least two-thirds of the Shares owned by all Stockholders
may effect any such waiver, modification, amendment or termination on behalf of
all of the Stockholders. To the extent any term or other provision of any other
indenture, agreement or instrument by which any party hereto is bound conflicts
with this Agreement, this Agreement shall have precedence over such conflicting
term or provision.

     12.  GOVERNING LAW; SUCCESSORS AND ASSIGNS. This Agreement shall be
governed by the laws of the State of Delaware and shall be binding upon the
heirs, personal representatives, executors, administrators, successors and
assigns of the parties.

     13.  WAIVERS. No waiver of any breach or default hereunder shall be
considered valid unless in writing, and no such waiver shall be deemed a waiver
of any subsequent breach or default of the same or similar nature.

     14.  SEVERABILITY. If any provision of this Agreement shall be held to be
illegal, invalid or unenforceable, such illegality, invalidity or
unenforceability shall attach only to such provision and shall not in any
manner affect or render illegal, and this Agreement shall be carried out as if
any such illegal, invalid or unenforceable provision were not contained herein.

<PAGE>

                                     - 9 -

     15.  CAPTIONS. Captions are for convenience only and are not deemed to be
part of this Agreement.

     16.  CONTINUATION OF EMPLOYMENT. Nothing in this Agreement shall create an
obligation on the Company to continue a Stockholder's employment with the
Company.

     17.  COUNTERPARTS. This Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

                 [Rest of this page intentionally left blank.]

<PAGE>

                                     - 10 -

     IN WITNESS WHEREOF, this Agreement has been executed as of the date and
year first above written.

                                        COMPANY:

                                        POLYMERS FOR MEDICINE, INC.

                                        By: /s/ Sherri C. Oberg
                                            ----------------------------------
                                        Title: President & CEO
                                             ---------------------------------
                                        Address: 157 Bristol Road
                                                 Wellesley, MA 02181

                                        STOCKHOLDERS:

                                        /s/ Robert S. Langer
                                        -------------------------------------
                                        Robert S. Langer

                                        Address: 77 Lombard Street
                                                 Newton, MA 02158

                                        /s/ Sherri C. Oberg
                                        -------------------------------------
                                        Sherri C. Oberg

                                        Address: 157 Bristol Road
                                                 Wellesley, MA 02181

                                        /s/ Harry R. Allcock
                                        -------------------------------------
                                        Harry R. Allcock

                                        Address: 434 Kemmerer Road
                                                 State College, PA 16801

                                        /s/ Walter J. Levison
                                        -------------------------------------
                                        Walter J. Levison

                                        Address: Aegis Venture Funds
                                                 55 Old Bedford Rd
                                                 Lincoln MA 01773

                                        /s/ Richard L. Kronenthal
                                        -------------------------------------
                                        Richard L. Kronenthal

                                        Address: 33 Garwood Road
                                                 Fair Lawn, NJ 07410

<PAGE>

                                    AMENDMENT

     This is an Amendment of the Amended and Restated Stockholders' Agreement
dated as of January 24, 1994 by and among polymers for Medicine, Inc., a
Delaware corporation (the ,Company") and Robert S. Langer, Sherri C. Oberg,
Harry R. Allcock, Walter Levison and Richard L. Kronenthal (the ,Agreement")
pursuant to Section 11 thereof.

     The Agreement is hereby amended by deleting in its entirety Section 4
("Right of Participation in Sales")

     In all other respects, the Agreement will remain in full force an~ effect
as written.

     IN WITNESS WHEREOF, this Amendment has been executed as of March 7, 1994.

COMPANY:                                STOCKHOLDERS:

POLYMERS FOR MEDICINE, INC.

By: Sherri C. Oberg                     /s/ Robert S. Langer
   --------------------------           -----------------------------------
Title: President & CEO                  Robert S. Langer
       ----------------------
                                        Address: 77 Lombard Street
                                                 Newton, MA 02158

                                        /s/ Sherri C. Oberg
                                        -----------------------------------
                                        Sherri C. Oberg

                                        Address: 157 Bristol Road
                                                 Wellesley, MA 02181

                                        /s/ Harry R. Allcock
                                        -----------------------------------
                                        Harry R. Allcock

                                        Address: 434 Kemmerer Road
                                                 State College, PA 16801

                                        /s/ Walter J. Levison
                                        -----------------------------------
                                        Walter J. Levison

                                        Address: Aegis Venture Funds
                                                 One Cranberry Hill
                                                 Lexington, MA 02173

                                        -----------------------------------
                                        Richard L. Kronenthal

                                        Address: 33 Garwood. Road
                                                 Fair Lawn, NJ 07410

<PAGE>

                                                                       EXHIBIT A

                                 AMENDMENT NO. 2

     This is an Amendment No. 2 of the Amended and Restated Stockholders'
Agreement dated as of January 24, 1994, as amended on March 7, 1994, by and
among Acusphere, Inc., a Delaware corporation (the "Company") and Robert S.
Langer, Sherri C. Oberg, Harry K. Allcock, Walter Levison and Richard L.
Kronenthal (the "Agreement") pursuant to Section 10 thereof.

     1.   The Agreement is hereby amended by deleting the words "or hereafter
          acquired" from Section 1(b) of the Agreement.

     In all other respects, the Agreement will remain in full force and effect
as written.

     IN WITNESS WHEREOF, this Amendment No. 2 has been executed as of
September__, 1995.

                                        COMPANY:

                                        ACUSPHERE, INC.

                                        By: Sherri C. Oberg
                                           ---------------------------------
                                        Title: President & CEO
                                              ------------------------------
                                        Address: 38 Sidney Street
                                                 Cambridge, MA 02139

                                        STOCKHOLDERS:

                                        /s/ Robert S. Langer
                                        ------------------------------------
                                        Robert S. Langer

                                        Address: 77 Lombard Street
                                                 Newton, MA 02158

                                        /s/ Sherri C. Oberg
                                        ------------------------------------
                                        Sherri C. Oberg
                                        Address: 157 Bristol Road
                                                 Wellesley, MA 02181

<PAGE>

                                        ------------------------------------
                                        Harry R: Allcock

                                        Address: 434 Kemmerer Road
                                                 State College, PA 16801

                                        ------------------------------------
                                        Walter J. Levison

                                        Address: 175 E. Barehill Road
                                                 Harvard, MA 01451

                                        ------------------------------------
                                        Richard L. Kronenthal

                                        Address: 33 Garwood Road
                                                 Fair Lawn, NJ 07410

<PAGE>

                               AMENDMENT NO. 3 TO
                  AMENDED AND RESTATED STOCKHOLDERS' AGREEMENT

         This Amendment No. 3 dated as of December __, 2001 (this "Amendment No.
3") amends that certain Amended and Restated Stockholders' Agreement (the
"Stockholders' Agreement") dated as of January 24, 1994, as amended by Amendment
No. 1 to the Amended and Restated Stockholders' Agreement dated as of March 7,
1994 and Amendment No. 2 to the Amended and Restated Stockholders' Agreement
dated as of September __, 1995, by and among Acusphere, Inc., a Delaware
corporation (the "Company"), and Robert S. Langer, Sherri C. Oberg, Harry R.
Allcock, Walter Levison and Richard L. Kronenthal.

1.       Amendment.

         1.1. The last sentence of Section 2 of the Stockholders' Agreement
shall be deleted in its entirety and replaced with the following:

         "As used herein, the word "family" shall include any spouse, lineal
         ancestor or descendant, brother or sister, or lineal ancestor of a
         spouse."

2.       Miscellaneous.

         2.1. Effect. Except as amended hereby, the Stockholders' Agreement
shall remain in full force and effect.

         2.2. Defined Terms. All capitalized terms used but not specifically
defined herein shall have the same meanings given such terms in the
Stockholders' Agreement unless the context clearly indicates or dictates a
contrary meaning.

         2.3. Governing Law. This Amendment No. 3 shall be governed by the laws
of the State of Delaware and shall be binding upon the heirs, personal
representatives, executors, administrators, successors and assigns of the
parties.

         2.4. Counterparts. This Amendment may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

<PAGE>

         IN WITNESS WHEREOF, this Amendment No. 3 has been executed as the date
first above written.

                                             COMPANY:

                                             ACUSPHERE, INC.

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

                                             Sherri C. Oberg,
                                             President

                                             Address: 38 Sidney Street
                                                      Cambridge, MA  02139

                                             STOCKHOLDERS:

                                             /s/ Robert Langer
                                             -----------------------------------
                                             Robert S. Langer

                                             Address: 98 Montvald Road
                                                      Newton, MA  02459

                                             /s/ Sherri C. Oberg
                                             -----------------------------------
                                             Sherri C. Oberg

                                             Address: 157 Bristol Road
                                                      Wellesley, MA  02181

                                             -----------------------------------
                                             Harry R. Allcock

                                             Address: 434 Kemmerer Road
                                                      State College, PA  16801

                                             -----------------------------------
                                             Ann R. Levison

                                             Address: 175 E. Barehill Road
                                                      Harvard, MA  01451

<PAGE>

                                           -------------------------------------
                                           Richard L. Kronenthal

                                           Address: 33 Garwood Road
                                                    Fair Lawn, NJ  07410

                                           THE ALISON OBERG IRREVOCABLE
                                           TRUST - 2000

                                           -------------------------------------
                                           Name:  Mary C. Carroll, Trustee
                                           Address:  603 Winsford Road
                                                     Bryn Mawr, PA  19010

                                           -------------------------------------
                                           Name:  A. David Carroll, III, Trustee
                                             Address:  603 Winsford Road
                                                       Bryn Mawr, PA  19010

                                           THE ERIC OBERG IRREVOCABLE
                                           TRUST - 2000

                                           -------------------------------------
                                           Name:  Mary C. Carroll, Trustee
                                           Address:  603 Winsford Road
                                                     Bryn Mawr, PA  19010

                                           -------------------------------------
                                           Name:  A. David Carroll, III, Trustee
                                           Address:  603 Winsford Road
                                                     Bryn Mawr, PA 19010

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