<PAGE>

                                                                   EXHIBIT 10.54

                           SONUS PHARMACEUTICALS, INC.
                          22026 20TH AVENUE, SUITE 201
                            BOTHELL, WASHINGTON 98021

                                   May 1, 2003

Michael B. Stewart, M.D.
c/o Sonus Pharmaceuticals, Inc.
22026 20th Avenue SE
Bothell, Washington  98021

Re: Change In Control Agreement

Dear Michael:

         In consideration of your continued employment with Sonus
Pharmaceuticals, Inc., a Delaware corporation (the "Company"), this letter
agreement ( the "Agreement") sets forth the compensation and benefits you will
be entitled to receive in the event your employment terminates in connection
with a change in control of the Company under the conditions described below.
This Agreement takes effect on the date set forth above.

1.       TERMINATION OF EMPLOYMENT.

         1.1.     During the term of this Agreement, you will be entitled to the
benefits provided in Section 2 of this Agreement in the event (A) a Change in
Control has occurred; and (B) (i) you terminate your employment with the Company
for Good Reason within 12 months following the Change of Control, or (ii) the
Company terminates your employment for reasons other than Cause, Disability, or
your death within 12 months following the Change of Control, provided you
fulfill your obligations under this Agreement.

         1.2      For purposes of this Agreement, the term "Change in Control"
shall mean (i) a sale of fifty percent (50%) or more of the outstanding shares
of common stock of the Company; (ii) a sale of all or substantially all of the
assets of the Company, or (iii) a merger, consolidation or reorganization
whereby the stockholders of the Company immediately prior to the consummation of
such merger, consolidation or reorganization own less than fifty percent (50%)
of the outstanding shares of common stock immediately following the consummation
of the merger, consolidation or reorganization.

         1.3.     For purposes of this Agreement, the term "Good Reason" shall
mean any of the following, if done without your consent:

                  1.3.1.   A substantial diminution in your duties and
responsibilities to a level substantially beneath that of your duties and
responsibilities at the outset of your employment under

<PAGE>

Michael B. Stewart, M.D.
May 1, 2003
Page 2

this Agreement other than actions that are not taken in bad faith and are
remedied by the Company within thirty days after written notice by you;

                  1.3.2.   A reduction by the Company in your current annual
base salary unless such reduction is attributable to an across the board salary
reduction for all of management personnel of the Company and then only if the
percentage of your reduction is (i) not greater than 20%, and (ii) no greater
than that of the other management personnel;

                  1.3.3.   The Company requires the relocation of your base of
employment outside the Seattle, Washington metropolitan area;

                  1.3.4.   A material breach by the Company of any of the terms
and provisions of this Agreement, which is not cured within 30 days of written
notice by you of such breach; or

                  1.3.5.   the failure of the Company to obtain a satisfactory
agreement from any successor in a Change of Control to assume and agree to
perform this Agreement, as contemplated in Section 6 hereof.

         1.4      For purposes of this Agreement, the term "Cause" shall mean
any of the following: (i) your willful and continued failure or refusal to
perform your duties with the Company; (b) your willfully engaging in gross
misconduct injurious to the Company; (c) your being convicted or pleading guilty
or nolo contendere to any misdemeanor involving moral turpitude or to any
felony; (d) your having materially breached any provision of this Agreement, or
any agreement concerning confidentiality or ownership of inventions with the
Company and failed to cure such breach to the reasonable satisfaction of the
Company within thirty (30) days following written notice of breach, if such cure
is possible.

         1.5.     For purposes of this Agreement, the term "Disability" shall
mean your inability to perform the essential functions of your position due to
any physical or mental illness even with reasonable accommodation to the extent
required by law, for any period of six months in the aggregate during any twelve
months, provided the Company has given you a written demand to return to your
fill time duties.

         1.6      Any termination of employment by you or by the Company
pursuant to this Agreement shall be communicated by written Notice of
Termination indicating the termination provision in this Agreement relied upon,
if any. For purposes of this Agreement, the "Date of Termination" shall mean the
date specified in the Notice of Termination which shall not be earlier than ten
(10) business days after the date on the Notice of Termination is given.

2.       COMPENSATION UPON TERMINATION.

         2.1.     If your employment shall be terminated and you are entitled to
benefits under Section 1 of this Agreement then, except as provided in
Subsection 2.2, you shall receive the following benefits:

                  2.1.1.   the Company shall pay to you in a lump sum within ten
days following the Date of Termination (a) your base salary unpaid through the
Date of Termination at the rate in effect

<PAGE>

Michael B. Stewart, M.D.
May 1, 2003
Page 3

as of the time of Notice of Termination and (b) an amount equal to the value as
of the Date of Termination of the deferred portion of any bonus which has been
declared but is unpaid under any incentive compensation plan or program of the
Company then in effect;

                  2.1.2.   the Company shall pay to you as severance pay in a
lump sum within thirty days following the Date of Termination an amount equal to
your highest annual base salary in effect any time during the twelve (12) month
period prior to the Date of Termination; and

                  2.1.3.   the Company shall maintain in full force and effect,
for the continued benefit of you for one year after the Date of Termination, or,
if sooner, until you are employed in a full-time capacity by another employer,
all non-cash health and welfare plans and programs (excluding 401(k) or any
employee bonus plans and programs or retirement plans or programs) in which you
participated immediately prior to the Date of Termination provided that your
continued participation is permissible under the general terms and provisions of
such plans and programs. In the event that your participation in any such plan
or program is barred, the Company shall arrange to provide you with benefits
substantially similar to those which you are entitled to receive under such
plans and programs at no cost to you. At the end of the period of coverage, you
shall have the option to have assigned to you at no cost and with no
apportionment of prepaid premiums, any assignable insurance policy owned by the
Company and relating to specifically to you.

         2.2.     Notwithstanding Section 1, the respective obligations of, and
benefits afforded to, the Company and you as provided in this Section 2, shall
survive termination of this Agreement.

         2.3.     No compensation or benefits shall be due under this Agreement
in the event your employment is terminated by you or the Company in
circumstances other than those described in Section 1.1, including but not
limited to a termination by you for any reason other than Good Reason, a
termination by the Company for Cause, disability, or death, or any termination
that does not occur within twelve months following a Change in Control.

         2.4.     To the extent that any or all of the payments and benefits
provided for in this Agreement constitute "parachute payments" within the
meaning of Section 280G of the Internal Revenue Code (the "Code") and, but for
this Section 2.4 would be subject to the excise tax imposed by Section 4999 of
the Code, the aggregate amount of such payments and benefits shall be reduced
such that the present value thereof (as determined under the Code and applicable
regulations) is equal to 2.99 times the Executive's "base amount" (as defined in
the Code). The determination of any reduction of any payment or benefits under
Section 2 pursuant to the foregoing provision shall be made by a nationally
recognized public accounting firm chosen by the Company in good faith, and such
determination shall be conclusive and binding on the Company and you.

3.       OTHER BENEFITS.

         In the event you are entitled to any compensation or benefits under
this Agreement, you shall not be entitled to any other severance compensation or
benefits under any other policy or agreement with the Company.

<PAGE>

Michael B. Stewart, M.D.
May 1, 2003
Page 4

4.       PROPRIETARY INFORMATION AND UNFAIR COMPETITION.

         4.1      You acknowledge that in the course of your employment with the
Company, you will be entrusted with access to extensive confidential information
of the Company concerning its products and service, methods of manufacture,
research and development, know-how, patents, copyrights, trademarks, and other
proprietary data, as well as the identity, needs, and preferences of its
customers and prospects, all of which the Company considers its legally
protected trade secrets and intellectual property. You further acknowledge the
highly competitive nature of the business of the Company, and the fact that
unauthorized disclosure or use of such trade secrets and intellectual property
would be inevitable if you were to compete with the Company or solicit competing
business from its prospects and customers. You therefore agree as follows:

         4.2      Commencing on the Date of Termination, and ending one year
thereafter (the "Non-Compete Period"), you will not provide goods or services to
or become an employee, owner (except for passive investments of not more than
three percent of the outstanding shares of, or any other equity interest in, any
company or entity listed or traded on a national securities exchange or in an
over-the-counter securities market), officer, agent, consultant, advisor or
director of any firm or person in any geographic area which competes in the
"Business". For purposes of this Agreement, the term "Business" shall mean the
research, design, development, manufacture, sale or distribution of drug
delivery products using the Company's Tocosol(TM) technology.

         4.3      During the Non-Compete Period, you will not directly or
indirectly induce any employee of the Company or any of its affiliates to engage
in any activity in which you are prohibited from engaging by paragraph 5.1
above, or to terminate such employee's employment with the Company, or any of
its affiliates, and will not directly or indirectly employ or offer employment
to any person who was employed by the Company or any of its affiliates unless
such person shall cease to be employed by the Company or any of its affiliates
for a period of at least 12 months; provided, however, that this provision shall
not apply to any person who is no longer an employee of the Company or any of
its affiliates as of a result of actions taken by the Company or its affiliates.

         4.4      During the Non-Compete Period, you will refrain from making
any statement which has the effect of demeaning the name or the business
reputation of the Company or its subsidiaries or affiliates, or any officer or
employee thereof, or which materially adversely effects the best interests
(economic or otherwise) of the Company, its subsidiaries or affiliates.

         4.5.     It is expressly understood and agreed that although you and
the Company consider the restrictions contained in this Section 5 to be
reasonable, if a final judicial determination is made by a court of jurisdiction
that the time or territory or any other restriction contained in this Agreement
is an unenforceable restriction against you, provisions of this Agreement shall
not be rendered void, but shall be deemed amended to apply to such maximum time
and territory and to such maximum extent as such court may judicially determine
or indicate to be enforceable. Alternatively, if any court of competent
jurisdiction finds that any restriction contained in this Agreement is
unenforceable, and such restriction cannot be amended so as to make it
enforceable, such finding shall not effect the enforceability of any of the
other restriction contained herein.

5.       MISCELLANEOUS.

<PAGE>

Michael B. Stewart, M.D.
May 1, 2003
Page 5

         Any payment required under this Agreement shall be subject to all
requirements of the law with regard to withholding, filing, making of reports
and the like, and the Company shall use its commercially reasonable best efforts
to satisfy promptly all such requirements. No provisions of this Agreement may
be modified, waived or discharged unless such waiver, modification or discharge
is agreed to in a writing signed by both parties. The validity, interpretation,
construction and performance of this Agreement shall be governed by the law of
the State of Delaware.

6.       SUCCESSORS AND ASSIGNMENT.

         This agreement and all of your rights thereunder shall inure to the
benefit of and be enforceable by your personal or legal representatives,
executors, administrators, successors, heirs, distributees, devisees and
legatees. Except as expressly provided in this Agreement, this Agreement is
personal to you and may not be assigned to you. If you should die while any
amounts would still be payable to you hereunder if you had continued to live,
all such amounts, unless otherwise provided herein, shall be paid in accordance
with the terms of this Agreement to your devisee, legatee, or other designee or,
if there be no such designee, to your estate. This Agreement shall be binding
upon any successor to the Company (whether direct or indirect, by purchase,
merger, consolidation or otherwise) to all or substantially all of the business
and/or assets of the Company.

7.       TERM OF AGREEMENT.

         This Agreement shall commence as of the date of this Agreement and
shall terminate on the earliest of (i) the termination of your employment by the
Company for Cause, Disability or death; (ii) your termination of employment
other than for Good Reason or (iii) your reaching age 65.

8.       NO GUARANTEE OF CONTINUED EMPLOYMENT.

         This Agreement is intended solely to provide you with certain
compensation and benefits in the event your employment terminates in the
circumstances described in Section 1.1. Nothing in this Agreement constitutes or
implies any specific term of employment. You acknowledge and agree that your
employment with the Company can be terminated by you or the Company at any time
with or without cause or prior warning. Nothing in this Agreement limits or
supercedes any other agreements between you and the Company concerning
confidentiality or ownership of intellectual property.

9.       MEDIATION

         In the event that the Company terminates you for Cause and you dispute
its right to do so or you claim that your are entitled to terminate your
employment for Good Reason and the Company disputes your right to do so, a
mediator acceptable to you and the Company will be appointed within ten (10)
days to assist in reaching a mutually satisfactory resolution but will have no
authority to issue a binding decision. Such mediation must be concluded within
60 days of the date of termination or claim to termination. Should such
mediation fail to reach an acceptable conclusion and you are successful in any
litigation or settlement that issues from such dispute, you shall be entitled to
receive from the Company all of the expenses incurred by you in connection with
any such dispute including reasonable attorney's fees.

<PAGE>

Michael B. Stewart, M.D.
May 1, 2003
Page 6

         If this Agreement is acceptable to you, kindly sign and return to the
Company the enclosed copy of this letter.

                                   Sincerely,

                                   Sonus Pharmaceuticals, Inc.

                                   /s/ Michael A. Martino
                                   -------------------------------------
                                   Micheal A. Martino
                                   President and Chief Executive Officer

AGREED AND ACCEPTED:

/s/ Michael B. Stewart M.D.
---------------------------
Michael B. Stewart, M.D.

Dated: May 15, 2003