EXHIBIT 5.1

                                  [LETTERHEAD]

November 19, 2002

Human BioSystems
1127 Harker Avenue
Palo Alto, California
94301

Re:  Human BioSystems Registration Statement on Form S-8 4,881,988 shares of
     Common Stock Issuable pursuant to Stock Option Plans

Gentlepersons:

        We are counsel to Human BioSystems, a California corporation, (the
"Company").  We have assisted the Company in its preparation of a Registration
Statement on Form S-8 (the "Registration Statement") under the Securities Act of
1933, as amended (the "Securities Act"), registering 4,881,988 shares of common
stock, no par value, of the Company (the "Common Stock") issuable pursuant to
the terms and conditions of the Company's 2001 Stock Option Plan, 1998 Statutory
Incentive Stock Option Plan and 1998 Non-Statutory Stock Option Plan
(collectively, the "Plans").

        In rendering this opinion, we have considered such questions of law and
examined such statutes and regulations, corporate records, certificates and
other documents and have made such other examinations, searches and
investigations as we have considered necessary.  In such examinations we have
assumed the genuineness of all signatures and the authenticity of all documents
submitted to us as originals and the conformity to original documents of all
documents submitted to us as certified or as photocopies or telecopies.  We have
not made an independent examination of the laws of any jurisdiction other than
California and the federal laws of the United States, and we do not express or
imply any opinions in respect to the laws of any other jurisdiction.  The
opinions expressed herein are based on legislation and regulations in effect on
the date hereof.

        Based on and subject to the foregoing, we are of the opinion that the
Common Stock, when issued pursuant to the terms of the Plans, will be duly and
validly issued, fully paid and nonassessable shares of Common Stock.

        We hereby consent to the filing of this opinion as an Exhibit to the
Registration Statement.  This consent is not to be construed as an admission
that we are a person whose consent is required to be filed with the Registration
Statement under the provisions of the Securities Act.

                                                Very truly yours,

                                        /s/ SILICON VALLEY LAW GROUP
                                        ----------------------------
                                            SILICON VALLEY LAW GROUP