September 19, 1997


                  [STRADLING, YOCCA, CARLSON & RAUTH LETTEREAD]

                               September 19, 1997


SONUS Pharmaceuticals, Inc.
22026 20th Avenue, S.E., Suite 102
Bothell, Washington  98021

        Re:    Registration Statement on Form S-8

Gentlemen:

               At your request, we have examined the form of Registration
Statement on Form S-8 (the "Registration Statement") being filed by SONUS
Pharmaceuticals, Inc., a Delaware corporation (the "Company"), with the
Securities and Exchange Commission in connection with the registration under the
Securities Act of 1933, as amended, of an additional 774,810 shares of the
Company's common stock, $.001 par value ("Common Stock"), issuable under the
Company's Incentive Stock Option, Nonqualified Stock Option and Restricted Stock
Purchase Plan - 1991 (the "Plan").

               We have examined the proceedings heretofore taken and are
familiar with the additional proceedings proposed to be taken by the Company in
connection with the authorization, issuance and sale of the securities referred
to above.

               Based on the foregoing, it is our opinion that the 774,810 shares
of Common Stock to be issued under the Plan against full payment in accordance
with the respective terms and conditions of the Plan will be legally and validly
issued, fully paid and nonassessable.

               We consent to the use of this opinion as an exhibit to the
Registration Statement.


                                Very truly yours,

                                STRADLING, YOCCA, CARLSON & RAUTH

                                /s/ Stradling, Yocca, Carlson & Rauth


EXHIBIT 5.1