EXHIBIT 5.1

OPINION OF COUNSEL

Snell & Wilmer LLP

600 Anton Boulevard

Suite 1400

Costa Mesa, California 92626-7689

TELEPHONE: (714) 427-7000

FACSIMILE: (714) 427-7799

December 12, 2005

Peregrine Pharmaceuticals, Inc.

14272 Franklin Avenue

Tustin, California 92780

Attention: Steven M. King, CEO

Re:Issuance of Shares Pursuant to S-8 Registration Statement

Dear Mr. King:

This letter relates to the issuance of up to 5,000,000 shares of common stock, $.001 par value (the “Shares”), of Peregrine Pharmaceuticals, Inc., a Delaware corporation (the “Company”) registered pursuant to that Registration Statement on Form S-8, filed with the Securities and Exchange Commission on December 12, 2005 (the “Registration Statement”). You have requested that we deliver to you an opinion as to whether the Shares will have been duly authorized, validly issued, and, when issued, will be fully paid and non-assessable shares of common stock of the Company. We have examined the Certificate of Incorporation, as amended, and such other corporate records, including the resolutions of the Company’s Board of Directors, and such other documents as we have deemed necessary in order to express the opinion set forth below. In our examination we have assumed the genuineness of all signatures and the authenticity of all documents submitted to us as originals and the conformity of all originals of all documents submitted to us as copies. As to questions of fact material to such opinion, we have relied upon statements and representations of the Company.

Our opinion is based on existing law that is subject to change either prospectively or retroactively. Relevant laws could change in a manner that could adversely affect the Company or its stockholders. We have no obligation to inform the Company of any such change in the law. We have not been requested to opine, and we have not opined, as to any issues other than those expressly set forth herein. This opinion extends only to questions relating to the validity of the Shares offered and sold under the Registration Statement. We express no opinion with respect to any other issue.

We are admitted to practice law in the State of California and our opinion is limited to federal law and the corporate laws of the State of California and the State of Delaware that affect such opinion. We express no opinion with respect to any other law or the laws of any other jurisdiction.

Based on our examination mentioned above, we are of the opinion that the Shares being registered to be sold pursuant to the Registration Statement are duly authorized and will be, when sold in the manner described in the Registration Statement and documents incorporated by reference thereto, legally and validly issued, and fully paid and non-assessable.

For purposes of rendering this opinion we have made such legal and factual inquiries as we have deemed necessary under the circumstances. Although we have not independently verified all of the facts relied upon for purposes hereof, nothing has come to our attention that has led us to believe that the facts are other than as stated herein, or that there exist other material facts not considered.

Our opinion contained herein is solely for the benefit of the Company and may be relied upon by the Company only in connection with the Registration Statement. In this regard, we hereby consent to the filing of this opinion, including this consent, as an exhibit to the Registration Statement.

     Very truly yours,

     /s/ Snell & Wilmer LLP