EXHIBIT 5.1
                          SILICON VALLEY LAW GROUP
                                 [LETTERHEAD]

May 14, 2004

Human BioSystems
1127 Harker Avenue
Palo Alto, California
94301

Re:     Human BioSystems Registration Statement on Form S-8

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 542,693  shares of common stock, no par
value, of the Company (the "Common Stock") issuable pursuant to the terms and
conditions of certain written agreements, concerning the conversion of debt, by
and between the Company and certain employees and consultants (collectively, the
"Agreements").

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 Agreements, will be duly and
validly issued, fully paid and nonassessable.

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
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                                                    SILICON VALLEY LAW GROUP