EXHIBIT 5.1
                                                                     -----------


                                September 8, 2003


Genelabs Technologies, Inc.
505 Penobscot Drive
Redwood City, CA 94063

                           Re:      Genelabs Technologies, Inc.
                                    Registration Statement on Form S-3.
                                    -----------------------------------

                  We have acted as special counsel to Genelabs Technologies,
Inc., a California corporation (the "Company"), in connection with the
preparation of the Registration Statement on Form S-3 (such Registration
Statement being hereinafter referred to as the "Registration Statement") filed
by the Company with the Securities and Exchange Commission (the "Commission")
with respect to the registration under the Securities Act of 1933, as amended
(the "Act"), of (i) the Company's (a) senior debt securities and subordinated
debt securities (collectively, the "Debt Securities"), which may be issued
pursuant to indentures (as amended or supplemented, the "Indentures"), between
the Company and the trustee (the "Trustee"), (b) shares of Preferred Stock (the
"Preferred Stock"); (c) shares of Common Stock (the "Common Stock"); and (d)
Warrants to purchase shares of the Company's Common Stock (the "Warrants").

                  This opinion is being furnished in accordance with the
requirements of Item 601(b)(5) of Regulation S-K under the Act.

                  In connection with this opinion, we have examined originals or
copies, certified or otherwise identified to our satisfaction, of (i) the
Registration Statement; (ii) forms of the Indentures filed as an exhibit to the
Registration Statement; (iii) the Amended and Restated Articles of Incorporation
(the "Articles of Incorporation") and the Amended and Restated Bylaws (the
"Bylaws") of the Company as currently in effect; (iv) a specimen certificate
representing the Common Stock; (v) the form of Warrant filed as an exhibit to
the Registration Statement; and (vi) certain resolutions of the Board of
Directors of the Company relating to the transactions contemplated by the
Registration Statement, the Trusts and related matters (the "Board
Resolutions"). We have also examined originals or copies, certified or otherwise
identified to our satisfaction, of such other documents, certificates and
records as we have deemed necessary or appropriate as a basis for the opinions
set forth herein.

                  In our examination, we have assumed the legal capacity of all
natural persons, the genuineness of all signatures, the authenticity of all
documents submitted to us as originals, the conformity to original documents of
all documents submitted to us as certified or photostatic copies and the
authenticity of the originals of such latter documents. In making our
examination of documents executed by parties other than the Company, we have
assumed that such parties had the power, corporate or other, to enter into and
perform all obligations thereunder and have also assumed the due authorization
by all requisite action, corporate or other, and execution and delivery by such
parties of such documents and the validity and binding effect thereof on such
parties.

                  As to any facts material to the opinions expressed herein that
we have not independently established or verified, we have relied upon oral or
written statements and representations of officers and other representatives of
the Company.

                  We do not express any opinion as to the laws of any
jurisdiction other than the laws of the States of California and New York.

                  Based upon and subject to the limitations, qualifications,
exceptions and assumptions set forth herein, we are of the opinion that:

                  1. With respect to any series of Debt Securities (the "Offered
Debt Securities"), when (i) the applicable Indenture has been duly authorized
executed and delivered by the Trustee, as qualified to act under the Trust
Indenture Act of 1939; (ii) the authorized officers of the Company have taken
all necessary corporate action to fix and determine the terms of the Offered
Debt Securities in accordance with the Board Resolutions; (iii) the terms of the
Offered Debt Securities and of their issuance and sale have been duly
established in conformity with the Indenture so as not to violate any applicable
law, the Articles of Incorporation or Bylaws, or result in a default under or
breach of any agreement or instrument binding upon the Company, and so as to
comply with any requirement or restriction imposed by any court or governmental
body having jurisdiction over the Company; (iv) the applicable Indenture has
been duly executed and delivered by the Company; and (v) the Offered Debt
Securities have been duly executed and authenticated in accordance with the
terms of the Indenture and duly delivered to the purchasers thereof upon payment
of the agreed-upon consideration therefor, the issuance and sale of the Offered
Debt Securities will have been duly authorized, and the Offered Debt Securities
will be valid and binding obligations of the Company entitled to the benefits of
the Indenture and enforceable against the Company in accordance with their
terms, except to the extent that (x) enforcement thereof may be limited by (1)
bankruptcy, insolvency, reorganization, fraudulent transfer, moratorium or
similar laws now or hereinafter in effect relating to or affecting the
enforcement of creditors' rights generally, (2) general principles of equity
(regardless of whether enforceability is considered in a proceeding at law or in
equity), and (3) governmental authority to limit, delay or prohibit the making
of payments outside the United States and (y) any waiver with respect to usury
laws.

                  2. With respect to the shares of any series of Preferred Stock
(the "Offered Preferred Stock"), when (i) the Board of Directors of the Company
or an authorized committee thereof has taken all necessary corporate action to
fix and determine the terms of the Offered Preferred Stock in accordance with
the Board Resolutions, including the adoption of a Certificate of Determination
for such Preferred Stock in the form required by applicable law; (ii) such
Certificate of Determination has been duly filed with the Secretary of State of
the State of California; (iii) certificates representing the shares of the
Offered Preferred Stock have been manually signed by an authorized officer of
the transfer agent and registrar for the Offered Preferred Stock and registered
by such transfer agent and registrar, and delivered to the purchasers thereof;
and (iv) the Company receives consideration per share for the Offered Preferred
Stock in such amount as may be determined by the Board of Directors of the
Company, or an authorized committee thereof, in a form legally valid under
Section 409 of the California General Corporation Law ("CGCL"), the issuance and
sale of the shares of Offered Preferred Stock will have been duly authorized,
and such shares will be validly issued, fully paid and nonassessable.

                  3. With respect to the shares of Common Stock (the "Offered
Common Stock"), when (i) the Board of Directors of the Company or an authorized
committee thereof has taken all necessary corporate action to authorize the
issuance and sale of the Offered Common Stock in accordance with the Board
Resolutions; (ii) certificates representing the shares of the Offered Common
Stock in the form of the specimen certificates examined by us have been manually
signed by an authorized officer of the transfer agent and registrar for the
Common Stock and registered by such transfer agent and registrar, and delivered
to the purchasers thereof; and (iii) the Company receives consideration per
share of the Offered Common Stock in a form legally valid under Section 409 of
the CGCL, the issuance and sale of the shares of Offered Common Stock, will have
been duly authorized, and such Offered Common Stock will be validly issued,
fully paid and nonassessable.

                  4. With respect to the Warrant and the shares of Common Stock
issued upon exercise thereof (the "Warrant Common Stock"), when (i) the Board of
Directors of the Company or an authorized committee thereof has taken all
necessary corporate action to authorize the issuance and sale of the Warrant and
the Warrant Common Stock in accordance with the Board Resolutions; (ii)
certificates representing the Warrant and the shares of the Warrant Common Stock
in the form of the Warrant and the specimen certificates examined by us have
been manually signed by an authorized officer of the transfer agent and
registrar for the Warrant and the Common Stock and registered by such transfer
agent and registrar, and delivered to the purchasers thereof; (iii) the Company
receives consideration for the Warrant in a form legally valid under Section 409
of the CGCL, and (iv) with respect to the Warrant Common Stock, the Warrant has
been exercised in accordance with its terms and the Company has received the
consideration provided thereunder, the issuance and sale of the Warrant and,
upon exercise thereof, the shares of Warrant Common Stock, will have been duly
authorized, and such Warrant and such shares of Warrant Common Stock will be
validly issued, fully paid and nonassessable.

                  We hereby consent to the filing of this opinion with the
Commission as an exhibit to the Registration Statement. We also consent to the
reference to our firm under the caption "Legal Matters" in the Registration
Statement. In giving this consent, we do not thereby admit that we are included
in the category of persons whose consent is required under Section 7 of the Act
or the rules and regulations of the Commission.

                         Very truly yours,


                  /s/ Skadden, Arps, Slate, Meagher & Flom LLP