EXHIBIT 5.1


                  [STRADLING YOCCA CARLSON & RAUTH LETTERHEAD]


                                February 6, 2002


Sonus Pharmaceuticals, Inc.
22026 20th Avenue S.E.
Bothell, Washington 98021

         Re:      Registration Statement on Form S-3

Ladies and Gentlemen:

         At your request, we have examined the Registration Statement on Form
S-3 to be filed by Sonus Pharmaceuticals, Inc., a Delaware corporation (the
"Company"), with the Securities and Exchange Commission (as may be amended or
supplemented, the "Registration Statement"), in connection with the registration
under the Securities Act of 1933 of 2,489,300 shares of Common Stock of the
Company, $.001 par value, (the "Securities"). The Securities may be sold from
time to time for the account of the selling stockholders set forth in the
Registration Statement.

         We have examined the proceedings heretofore taken and are familiar with
additional proceedings proposed to taken by you in connection with the
authorization, issuance and sale of the Securities.

         Based on the foregoing, and assuming that the full consideration for
the Securities has been received by the Company, it is our opinion that the
Securities, when issued and sold in the manner described in the Registration
Statement, will be legally issued, fully paid and nonassessable.

         We consent to the use of this opinion as an exhibit to the Registation
Statement and to the use of our name under the caption "Legal Matters" in the
Prospectus which is a part of the Registration Statement.

                                                 Very truly yours,

                                                 STRADLING YOCCA CARLSON & RAUTH

                                             /s/ Stradling Yocca Carlson & Rauth