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                                                                   Exhibit 10.03
                                 ACUSPHERE, INC.

                        2003 EMPLOYEE STOCK PURCHASE PLAN

ARTICLE 1 - PURPOSE.

      This 2003 Employee Stock Purchase Plan (the "Plan") is intended to
encourage stock ownership by all eligible employees of Acusphere, Inc. (the
"Company"), a Delaware corporation, and its participating subsidiaries (as
defined in Article 17) so that they may share in the growth of the Company by
acquiring or increasing their proprietary interest in the Company. The Plan is
designed to encourage eligible employees to remain in the employ of the Company
and its participating subsidiaries. The Plan is intended to constitute an
"employee stock purchase plan" within the meaning of Section 423(b) of the
Internal Revenue Code of 1986, as amended (the "Code"). Purchase options are to
be granted under the Plan only to employees of the Company or its subsidiaries
as provided in Article 3.

ARTICLE 2 - ADMINISTRATION OF THE PLAN.

      The Plan may be administered by a committee appointed by the Board of
Directors of the Company (the "Committee"). The Committee shall consist of not
less than two members of the Company's Board of Directors. The Board of
Directors may from time to time remove members from, or add members to, the
Committee. Vacancies on the Committee, howsoever caused, shall be filled by the
Board of Directors. The Committee may select one of its members as Chairperson,
and shall hold meetings at such times and places as it may determine. Acts by a
majority of the Committee, or acts reduced to or approved in writing by a
majority of the members of the Committee, shall be the valid acts of the
Committee.

      The interpretation and construction by the Committee of any provisions of
the Plan or of any purchase option granted under it shall be final, unless
otherwise determined by the Board of Directors. The Committee may from time to
time adopt such rules and regulations for carrying out the Plan as it may deem
best, provided that any such rules and regulations shall be applied on a uniform
basis to all employees under the Plan. No member of the Board of Directors or
the Committee shall be liable for any action or determination made in good faith
with respect to the Plan or any purchase option granted under it.

      In the event the Board of Directors fails to appoint or refrains from
appointing a Committee, the Board of Directors shall have all power and
authority to administer the Plan. In such event, the word "Committee" wherever
used herein shall be deemed to mean the Board of Directors.

ARTICLE 3 - ELIGIBLE EMPLOYEES.

      All employees of the Company or any of its participating subsidiaries
whose customary employment is more than 20 hours per week and for more than five
months in any calendar

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year shall be eligible to receive purchase options under the Plan to purchase
common stock of the Company, and all eligible employees shall have the same
rights and privileges hereunder. Persons who are eligible employees on the first
business day of any Payment Period (as defined in Article 5) shall receive their
purchase options as of such day. Persons who become eligible employees after any
date on which purchase options are granted under the Plan shall be granted
purchase options on the first day of the next succeeding Payment Period on which
purchase options are granted to eligible employees under the Plan. In no event,
however, may an employee be granted a purchase option if such employee,
immediately after the purchase option was granted, would be treated as owning
stock possessing five percent or more of the total combined voting power or
value of all classes of stock of the Company or of any parent corporation or
subsidiary corporation, as the terms "parent corporation" and "subsidiary
corporation" are defined in Section 424(e) and (f) of the Code. For purposes of
determining stock ownership under this paragraph, the rules of Section 424(d) of
the Code shall apply, and stock which the employee may purchase under
outstanding purchase options shall be treated as stock owned by the employee.

ARTICLE 4 - STOCK SUBJECT TO THE PLAN.

      The stock subject to the purchase options under the Plan shall be shares
of the Company's authorized but unissued common stock, par value $0.01 per share
(the "Common Stock"), or shares of Common Stock reacquired by the Company,
including shares purchased in the open market. The aggregate number of shares
which may be issued pursuant to the Plan is one million four hundred thousand
(1,400,000), subject to adjustment as provided in Article 12. If any purchase
option 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 in part, the unpurchased shares subject thereto shall again be
available under the Plan.

ARTICLE 5 - PAYMENT PERIOD AND PURCHASE OPTIONS.

      The first Payment Period during which payroll deductions will be
accumulated under the Plan shall commence on the effective date of the
registration statement on Form S-1 registering the shares to be offered in the
initial public offering of the Common Stock (the "Offering") and shall end on
February 29, 2004 (the "First Payment Period"). For the remainder of the
duration of the Plan, Payment Periods shall consist of the six-month periods
commencing on September 1 and March 1 and ending on the last days of February
and August of each calendar year.

      Twice each year, on the first business day of each Payment Period, the
Company will grant to each eligible employee who is then a participant in the
Plan a purchase option to purchase on the last day of such Payment Period, at
the Option Price hereinafter provided for, a maximum of 2,500 shares, on
condition that such employee remains eligible to participate in the Plan
throughout the remainder of such Payment Period. The participant shall be
entitled to exercise the purchase option so granted only to the extent of the
participant's accumulated payroll deductions on the last day of such Payment
Period. If the participant's accumulated payroll deductions on the last day of
the Payment Period would enable the participant to purchase more than 2,500
shares except for the 2,500-share limitation, the excess of the amount of the
accumulated payroll deductions over the aggregate purchase price of the 2,500
shares shall be

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promptly refunded to the participant by the Company, without interest. The
Option Price per share for each Payment Period shall be the lesser of (i) 85% of
the average market price of the Common Stock on the first business day of the
Payment Period and (ii) 85% of the average market price of the Common Stock on
the last business day of the Payment Period, in either event rounded up to the
nearest cent. The foregoing limitation on the number of shares subject to
purchase option and the Option Price shall be subject to adjustment as provided
in Article 12.

      For purposes of the Plan, the term "average market price" on any date
means (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 average of the closing bid and asked prices
last 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; or (iv) if the Common Stock is not publicly traded, the fair
market 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. Notwithstanding the foregoing, the
"average market price" of Common Stock on the first business day of the First
Payment Period shall equal the price per share at which the Common Stock is sold
to the underwriters in the Offering, without regard to any applicable discounts
or commissions provided to such underwriters.

      For purposes of the Plan, the term "business day" means a day on which
there is trading on the NASDAQ National Market or the aforementioned national
securities exchange, whichever is applicable pursuant to the preceding
paragraph; and if neither is applicable, a day that is not a Saturday, Sunday or
legal holiday in the Commonwealth of Massachusetts.

      No employee shall be granted a purchase option which permits the
employee's right to purchase stock under the Plan, and under all other Section
423(b) employee stock purchase plans of the Company and any parent or subsidiary
corporations, to accrue at a rate which exceeds $25,000 of fair market value of
such stock (determined on the date or dates that purchase options on such stock
were granted) for each calendar year in which such purchase option is
outstanding at any time. The purpose of the limitation in the preceding sentence
is to comply with Section 423(b)(8) of the Code. If the participant's
accumulated payroll deductions on the last day of the Payment Period would
otherwise enable the participant to purchase Common Stock in excess of the
Section 423(b)(8) limitation described in this paragraph, the excess of the
amount of the accumulated payroll deductions over the aggregate purchase price
of the shares actually purchased shall be promptly refunded to the participant
by the Company, without interest.

ARTICLE 6 - EXERCISE OF PURCHASE OPTION.

      Each eligible employee who continues to be a participant in the Plan on
the last day of a Payment Period shall be deemed to have exercised his or her
purchase option on such date and shall be deemed to have purchased from the
Company such number of full shares of Common

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Stock reserved for the purpose of the Plan as the participant's accumulated
payroll deductions on such date will pay for at the Option Price, subject to the
2,500-share limit of the purchase option and the Section 423(b)(8) limitation
described in Article 5. If the individual is not a participant on the last day
of a Payment Period, he or she shall not be entitled to exercise his or her
purchase option. Only full shares of Common Stock may be purchased under the
Plan. Unused payroll deductions remaining in a participant's account at the end
of a Payment Period by reason of the inability to purchase a fractional share
shall be carried forward to the next Payment Period.

ARTICLE 7 - AUTHORIZATION FOR ENTERING THE PLAN.

      An employee may elect to enter the Plan by filling out, signing and
delivering to the Company an authorization:

                  A.       Stating the percentage to be deducted regularly from
      the employee's pay;

                  B.       Authorizing the purchase of stock for the employee in
      each Payment Period in accordance with the terms of the Plan; and

                  C.       Specifying the exact name or names in which stock
      purchased for the employee is to be issued as provided under Article 11
      hereof.

Such authorization must be received by the Company before the first day of the
next succeeding Payment Period and shall take effect only if the employee is an
eligible employee on the first business day of such Payment Period, provided,
however, that with respect to the First Payment Period, a purchase option shall
be granted to each eligible employee and such authorization to participate in
the plan must be received no more than three weeks following the first day of
the First Payment Period.

      Unless a participant files a new authorization or withdraws from the Plan,
the deductions and purchases under the authorization the participant has on file
under the Plan will continue from one Payment Period to succeeding Payment
Periods as long as the Plan remains in effect.

      The Company will accumulate and hold for each participant's account the
amounts deducted from his or her pay. No interest will be paid on these amounts.

ARTICLE 8 - MAXIMUM AMOUNT OF PAYROLL DEDUCTIONS.

      An employee may authorize payroll deductions in an amount (expressed as a
whole percentage or fixed amount) not more than ten percent (10%) of the
employee's total compensation, including base pay or salary and any overtime,
bonuses or commissions.

ARTICLE 9 - CHANGE IN PAYROLL DEDUCTIONS.

      Deductions may not be increased or decreased during a Payment Period.
However, a participant may withdraw in full from the Plan.

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ARTICLE 10 - WITHDRAWAL FROM THE PLAN.

      A participant may withdraw from the Plan (in whole but not in part) at any
time prior to the last day of a Payment Period by delivering a withdrawal notice
to the Company.

      To re-enter the Plan, an employee who has previously withdrawn must file a
new authorization before the first day of the next Payment Period in which he or
she wishes to participate. The employee's re-entry into the Plan becomes
effective at the beginning of such Payment Period, provided that he or she is an
eligible employee on the first business day of the Payment Period.

ARTICLE 11 - ISSUANCE OF STOCK.

      Certificates for stock issued to participants shall be delivered as soon
as practicable after each Payment Period by the Company's transfer agent.
Certificates may be issued in paper or electronic form at the discretion of the
Company.

      Stock purchased under the Plan shall be issued only in the name of the
participant, or if the participant's authorization so specifies, in the name of
the participant.

ARTICLE 12 - ADJUSTMENTS.

      Upon the happening of any of the following described events subsequent to
the close of the Offering, a participant's rights under purchase options granted
under the Plan shall be adjusted as hereinafter provided:

                  A.       In the event that the shares of Common Stock shall be
      subdivided or combined into a greater or smaller number of shares or if,
      upon a reorganization, split-up, liquidation, recapitalization or the like
      of the Company, the shares of Common Stock shall be exchanged for other
      securities of the Company, each participant shall be entitled, subject to
      the conditions herein stated, to purchase such number of shares of Common
      Stock or amount of other securities of the Company as were exchangeable
      for the number of shares of Common Stock that such participant would have
      been entitled to purchase except for such action, and appropriate
      adjustments shall be made in the purchase price per share to reflect such
      subdivision, combination or exchange; and

                  B.       In the event the Company shall issue any of its
      shares as a stock dividend upon or with respect to the shares of stock of
      the class which shall at the time be subject to a purchase option
      hereunder, each participant upon exercising such a purchase option shall
      be entitled to receive (for the purchase price paid upon such exercise)
      the shares as to which the participant is exercising his or her purchase
      option and, in addition thereto (at no additional cost), such number of
      shares of the class or classes in which such stock dividend or dividends
      were declared or paid, and such amount of cash in lieu of fractional
      shares, as is equal to the number of shares thereof and the amount of cash
      in lieu of fractional shares, respectively, which the participant would
      have received if the participant had been the

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      holder of the shares as to which the participant is exercising his or her
      purchase option at all times between the date of the granting of such
      purchase option and the date of its exercise.

      Upon the happening of any of the foregoing events, the class and aggregate
number of shares set forth in Article 4 hereof which are subject to purchase
options which have been or may be granted under the Plan and the limitations set
forth in the second paragraph of Article 5 shall also be appropriately adjusted
to reflect the events specified in paragraphs A and B above. Notwithstanding the
foregoing, any adjustments made pursuant to paragraphs A or B shall be made only
after the Committee, based on advice of counsel for the Company, determines
whether such adjustments would constitute a "modification" (as that term is
defined in Section 424 of the Code). If the Committee determines that such
adjustments would constitute a modification, it may refrain from making such
adjustments.

      If the Company is to be consolidated with or acquired by another entity in
a merger, a 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, with respect to purchase options then outstanding under the Plan, either
(i) make appropriate provision for the continuation of such purchase options by
arranging for the substitution on an equitable basis for the shares then subject
to such purchase options either (a) the consideration payable with respect to
the outstanding shares of the Common Stock in connection with the Acquisition,
(b) shares of stock of the successor corporation, or a parent or subsidiary of
such 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 purchase options
immediately preceding the Acquisition; or (ii) terminate each participant's
purchase options in exchange for a cash payment equal to the excess of (a) the
fair market value on the date of the Acquisition, of the number of shares of
Common Stock that the participant's accumulated payroll deductions as of the
date of the Acquisition could purchase, at a purchase option price determined
with reference only to the first business day of the applicable Payment Period
and subject to the 2,500-share, Code Section 423(b)(8) and fractional-share
limitations on the amount of stock a participant would be entitled to purchase,
over (b) the result of multiplying such number of shares by such purchase option
price.

      The Committee or Successor Board shall determine the adjustments to be
made under this Article 12, and its determination shall be conclusive.

ARTICLE 13 - NO TRANSFER OR ASSIGNMENT OF EMPLOYEE'S RIGHTS.

      A purchase option granted under the Plan may not be transferred or
assigned and may be exercised only by the participant.

ARTICLE 14 - TERMINATION OF EMPLOYEE'S RIGHTS.

      Whenever a participant ceases to be an eligible employee because of
retirement, voluntary or involuntary termination, resignation, layoff,
discharge, death or for any other reason, his or her rights under the Plan shall
immediately terminate, and the Company shall promptly refund,

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without interest, the entire balance of his or her payroll deduction account
under the Plan. Notwithstanding the foregoing, eligible employment shall be
treated as continuing intact while a participant is on military leave, sick
leave or other bona fide leave of absence, for up to 90 days, or for so long as
the participant's right to re-employment is guaranteed either by statute or by
contract, if longer than 90 days.

ARTICLE 15 - TERMINATION AND AMENDMENTS TO PLAN.

      Unless terminated sooner as provided below, the Plan shall terminate on
July 31, 2013. The Plan may be terminated at any time by the Company's Board of
Directors but such termination shall not affect purchase options then
outstanding under the Plan. It will terminate in any case when all or
substantially all of the unissued shares of stock reserved for the purposes of
the Plan have been purchased. If at any time shares of stock reserved for the
purpose of the Plan remain available for purchase but not in sufficient number
to satisfy all then unfilled purchase requirements, the available shares shall
be apportioned among participants in proportion to the amount of payroll
deductions accumulated on behalf of each participant that would otherwise be
used to purchase stock, and the Plan shall terminate. Upon such termination or
any other termination of the Plan, all payroll deductions not used to purchase
stock will be refunded, without interest.

      The Committee or the Board of Directors may from time to time adopt
amendments to the Plan provided that, without the approval of the stockholders
of the Company, no amendment may (i) increase the number of shares that may be
issued under the Plan; (ii) change the class of employees eligible to receive
purchase options under the Plan, if such action would be treated as the adoption
of a new plan for purposes of Section 423(b) of the Code; or (iii) cause Rule
16b-3 under the Securities Exchange Act of 1934 to become inapplicable to the
Plan.

ARTICLE 16 - LIMITS ON SALE OF STOCK PURCHASED UNDER THE PLAN.

      The Plan is intended to provide shares of Common Stock for investment and
not for resale. The Company does not, however, intend to restrict or influence
any employee in the conduct of his or her own affairs. An employee may,
therefore, sell stock purchased under the Plan at any time the employee chooses,
subject to compliance with the Company's insider trading policy, as amended and
in effect from time to time, any applicable federal or state securities laws and
subject to any restrictions imposed under Article 21 to ensure that tax
withholding obligations are satisfied. THE EMPLOYEE ASSUMES THE RISK OF ANY
MARKET FLUCTUATIONS IN THE PRICE OF THE STOCK.

ARTICLE 17 - PARTICIPATING SUBSIDIARIES.

      The term "participating subsidiary" shall mean any present or future
subsidiary of the Company, as that term is defined in Section 424(f) of the
Code, which is designated from time to time by the Board of Directors to
participate in the Plan. The Board of Directors shall have the power to make
such designation before or after the Plan is approved by the stockholders.

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ARTICLE 18 - OPTIONEES NOT STOCKHOLDERS.

      Neither the granting of a purchase option to an employee nor the
deductions from his or her pay shall constitute such employee a stockholder of
the shares covered by a purchase option until such shares have been actually
purchased by the employee.

ARTICLE 19 - APPLICATION OF FUNDS.

      The proceeds received by the Company from the sale of Common Stock
pursuant to purchase options granted under the Plan will be used for general
corporate purposes.

ARTICLE 20 - NOTICE TO COMPANY OF DISQUALIFYING DISPOSITION.

      By electing to participate in the Plan, each participant agrees to notify
the Company in writing immediately after the participant transfers Common Stock
acquired under the Plan, if such transfer occurs within two years after the
first business day of the Payment Period in which such Common Stock was
acquired. Each participant further agrees to provide any information about such
a transfer as may be requested by the Company or any subsidiary corporation in
order to assist it in complying with the tax laws. Such dispositions generally
are treated as "disqualifying dispositions" under Sections 421 and 424 of the
Code, which have certain tax consequences to participants and to the Company and
its participating subsidiaries.

ARTICLE 21 - WITHHOLDING OF ADDITIONAL INCOME TAXES.

      By electing to participate in the Plan, each participant acknowledges that
the Company and its participating subsidiaries are required to withhold taxes
with respect to the amounts deducted from the participant's compensation and
accumulated for the benefit of the participant under the Plan, and each
participant agrees that the Company and its participating subsidiaries may
deduct additional amounts from the participant's compensation, when amounts are
added to the participant's account, used to purchase Common Stock or refunded,
in order to satisfy such withholding obligations. Each participant further
acknowledges that when Common Stock is purchased under the Plan the Company and
its participating subsidiaries may be required to withhold taxes with respect to
all or a portion of the difference between the fair market value of the Common
Stock purchased and its purchase price, and each participant agrees that such
taxes may be withheld from compensation otherwise payable to such participant.
It is intended that tax withholding will be accomplished in such a manner that
the full amount of payroll deductions elected by the participant under Article 7
will be used to purchase Common Stock. However, if amounts sufficient to satisfy
applicable tax withholding obligations have not been withheld from compensation
otherwise payable to any participant, then, notwithstanding any other provision
of the Plan, the Company may withhold such taxes from the participant's
accumulated payroll deductions and apply the net amount to the purchase of
Common Stock, unless the participant pays to the Company, prior to the exercise
date, an amount sufficient to satisfy such withholding obligations. Each
participant further acknowledges that the Company and its participating
subsidiaries may be required to withhold taxes in connection with the
disposition of stock acquired under the Plan and agrees that the Company or any
participating subsidiary may take

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whatever action it considers appropriate to satisfy such withholding
requirements, including deducting from compensation otherwise payable to such
participant an amount sufficient to satisfy such withholding requirements or
conditioning any disposition of Common Stock by the participant upon the payment
to the Company or such subsidiary of an amount sufficient to satisfy such
withholding requirements.

ARTICLE 22 - GOVERNMENTAL REGULATIONS.

      The Company's obligation to sell and deliver shares of Common Stock under
the 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
identify shares of Common Stock issued under the Plan on its stock ownership
records and send tax information statements to employees and former employees
who transfer title to such shares.

ARTICLE 23 - GOVERNING LAW.

      The validity and construction of the Plan shall be governed by the laws of
Delaware, without giving effect to the principles of conflicts of law thereof.

ARTICLE 24 - APPROVAL OF BOARD OF DIRECTORS AND STOCKHOLDERS OF THE COMPANY.

      The Plan was adopted by the Board of Directors on July 30, 2003 and was
approved by the stockholders of the Company on August __, 2003.

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