EXHIBIT 99.01

                                 August 13, 2003

Cepheid
904 Caribbean Avenue
Sunnyvale, California, 94089-1189

Gentlemen/Ladies:

        At your request, we have examined the Registration Statement on Form S-3
(File Number 333-75596) (the "REGISTRATION STATEMENT") filed by Cepheid, a
California corporation (the "COMPANY"), with the Securities and Exchange
Commission (the "COMMISSION") on December 20, 2001, as subsequently supplemented
by the prospectuses filed with the Commission on July 16, 2002 and February 28,
2003, and the prospectus supplement applicable to the "Offering" (as defined
below), in connection with the registration under the Securities Act of 1933, as
amended, of an aggregate of up to $35,000,000 of the Company's debt securities,
preferred stock, shares of common stock or warrants to purchase debt securities,
preferred stock or common stock, as described under "Securities to be
Registered" in the Registration Statement (the "SECURITIES"). With the
prospectus and prospectus supplements which comprise part of the Registration
Statement, the Company may offer and sell the Securities from time to time on a
delayed or continuous basis.

        The Company currently proposes to sell up to an aggregate of 2,777,778
shares (the "TAKEDOWN SHARES") of the Company's Common Stock, no par value per
share (the "COMMON STOCK"), under the Registration Statement (the "OFFERING") to
an investor (the "INVESTOR") pursuant to a stock purchase agreement ("STOCK
PURCHASE AGREEMENT"), dated August 13, 2003, between the Company and the
Investor.

        In rendering this opinion, we have examined such matters of fact as we
have deemed necessary in order to render the opinion set forth herein, which
included examination of the following.

        (1)    the Company's Fifth Amended and Restated Articles of
               Incorporation, as amended by the Certificate of Determination for
               the Series A Junior Preferred Stock filed on September 30, 2002,
               certified by the California Secretary of State on August 7, 2003.

        (2)    the Company's Amended and Restated Bylaws, certified by the
               Company's Secretary on August 13, 2003.

        (3)    the Registration Statement, together with the Exhibits filed as a
               part thereof or incorporated therein by reference.



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        (4)    the prospectus comprising part of the Registration Statement, as
               supplemented on July 16, 2002 and February 28, 2003 (the "BASE
               PROSPECTUS"), and the accompanying prospectus supplement
               applicable to the Offering ("PROSPECTUS SUPPLEMENT").

        (5)    the resolutions of the Company's Board of Directors (the "BOARD")
               adopted at a meeting held on December 5, 2001 approving the
               filing of the registration statement, the resolutions of the
               Board adopted at a meeting held on July 23, 2003 establishing a
               pricing committee of the Board ("the "PRICING COMMITTEE") and
               approving the Stock Purchase Agreement and authorizing the
               issuance of common stock pursuant to the Registration Statement
               in an amount and at a price determined by the Pricing Committee.

         (6)   the resolutions of the Pricing Committee adopted at a meeting
               held August 12, 2003, approving the terms of the Offering,
               including the number of Takedown Shares to be offered and the
               price per share at which such Takedown Shares are to be offered
               in the Offering.

        (7)    a certificate from the Company's transfer agent of even date
               herewith verifying the number of the Company's issued and
               outstanding shares of capital stock as of August 5, 2003 and a
               list of option and warrant holders respecting the Company's
               capital and of any rights to purchase capital stock that was
               prepared by the Company and dated August 8, 2003 verifying the
               number of such issued and outstanding securities.

        (8)    a Management Certificate addressed to us and dated of even date
               herewith executed by the Company containing certain factual
               representations (the "MANAGEMENT CERTIFICATE").

        (9)    the Current Report on Form 8-K with which this opinion is filed
               as an exhibit.

        (10)   the Financial Advisor Agreement, dated August 13, 2003, by and
               between the Company and UBS Securities LLC (the "FINANCIAL
               ADVISOR AGREEMENT").

        (11)   the Stock Purchase Agreement.

        (12)   the form of certificate representing shares of Common Stock.

        In our examination of documents for purposes of this opinion, we have
assumed, and express no opinion as to, the authenticity and completeness of all
documents submitted to us as originals, the genuineness of all signatures on
original documents, the conformity to originals and completeness of all
documents submitted to us as copies, the legal capacity of all persons or
entities executing the same, the lack of any undisclosed termination,
modification, waiver or amendment to any documents reviewed by us, and the due
authorization, execution and delivery of all documents where authorization, due
execution and delivery are prerequisites to the effectiveness thereof. We have
also assumed that, if and to the extent that the Takedown Shares are issued in
certificated form, the certificates representing the Takedown Shares will be,
when



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Page 3

issued, in the form of the certificate reviewed by us and properly signed
by authorized officers of the Company or their agents.

        As to matters of fact relevant to this opinion, we have relied solely
upon our examination of the documents referred to above and have assumed the
current accuracy and completeness of the information included in the documents
referred to above and the representations and warranties made by representatives
of the Company to us, including but not limited to those set forth in the
Management Certificate. We have made no independent investigation or other
attempt to verify the accuracy of any of such information or to determine the
existence or non-existence of any other factual matters; however, we are not
aware of any facts that would cause us to believe that the opinions expressed
herein are not accurate.

        In connection with our opinion expressed below, we have assumed that, at
or prior to the time of the delivery of any of the Takedown Shares, there will
not have occurred any change in law affecting the validity of the Takedown
Shares.

        We are admitted to practice law in the State of California, and we
render this opinion only with respect to, and express no opinion herein
concerning the application or effect of the laws of any jurisdiction other than,
the existing laws of the United States of America and of the State of
California.

        Based upon the foregoing, it is our opinion that the Takedown Shares,
when issued, sold and delivered in the manner and for the consideration stated
in the Registration Statement, the Base Prospectus, and Prospectus Supplement
and pursuant to the terms of the Stock Purchase Agreement, will be validly
issued, fully paid and nonassessable.

        We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to all references to us, if any, in the
Registration Statement, the Base Prospectus and Prospectus Supplement
constituting a part thereof and any amendments thereto. This opinion is intended
solely for use in connection with the issuance and sale of Takedown Shares
subject to the Registration Statement and is not to be relied upon for any other
purpose. This opinion speaks as of the date first above written, and we assume
no obligation to advise you of any fact, circumstance, event or change in the
law or the facts that may hereafter be brought to our attention whether or not
such occurrence would affect or modify the opinions expressed herein.

                                            Very truly yours,

                                            FENWICK & WEST LLP

                                            By: /s/ Douglas N. Cogen
                                                --------------------------------
                                                Douglas N. Cogen, a Partner