EXHIBIT 99.03

                            STOCK PURCHASE AGREEMENT

         STOCK PURCHASE AGREEMENT (this "Agreement"), dated as of August 1,
2002, by and between Cepheid a California corporation (the "Company"), and the
investor named on the signature page hereof (the "Investor").

                                   WITNESSETH

         WHEREAS, the Company has filed with the Securities and Exchange
Commission (the "Commission") the Registration Statement (as defined below)
relating to the offer and sale from time to time of the Company's securities,
including shares of its Common Stock, no par value ("Common Stock");

         WHEREAS, the Company is offering for sale shares of its Common Stock
(the "Offered Shares") pursuant to the Registration Statement; and

         WHEREAS, the Investor desires to purchase from the Company shares of
Common Stock on the terms and conditions set forth herein.

         NOW, THEREFORE, in consideration of the recitals (which are deemed to
be a part of this Agreement), mutual covenants, representations, warranties and
agreements contained herein and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto
agree as follows:

   1.   Definitions. As used herein, the following terms have the meanings
        indicated:

         "Person" shall mean any individual, partnership, limited liability
         company, joint venture, firm, corporation, association, trust or other
         enterprise or any government or political subdivision or any agency,
         department or instrumentality thereof.

         "Prospectus" shall mean the final base prospectus dated May 29, 2002
         forming a part of the Registration Statement. References herein to the
         term "Prospectus" as of any date shall mean such prospectus, as amended
         or supplemented to such date, including by the Prospectus Supplement
         (as defined below), and including all documents incorporated by
         reference therein as of such date.

         "Prospectus Supplement" shall mean the supplement to the Prospectus
         dated July 31, 2002 relating to the sale of the Offered Shares.

         "Registration Statement" shall mean the registration statement on Form
         S-3 (File No. 333-75596), including a prospectus, relating to the offer
         and sale of certain of the Company's securities, including its Common
         Stock, which was declared effective by the Commission on May 29, 2002.
         References herein to the term "Registration Statement" as of any date
         shall mean such registration statement, as amended or supplemented to
         such date, including all documents incorporated by reference therein as
         of such date.

2.       Purchase of Common Stock. Subject and pursuant to the terms and
         conditions set forth in this Agreement, the Company agrees that it will
         issue and sell to the Investor and the Investor agrees that it will
         purchase from the Company the number of Offered Shares set forth on
         Schedule I attached hereto (the "Investor Shares") at the price per
         share of Common Stock (the "Per Share


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         Purchase Price") set forth on Schedule I hereto. The aggregate purchase
         price for the Investor Shares (the "Aggregate Purchase Price") is set
         forth on Schedule I hereto. The closing of the purchase and sale of the
         Investor Shares will be on the date set forth on Schedule I hereto, or
         such other date as the parties may agree upon in writing (the
         "Closing").

3.  Deliveries at Closing.


          (a)  Deliveries by the Investor. At the Closing, the Investor shall
               deliver to the Company the following:

                  (1)      the Aggregate Purchase Price by wire transfer of
                           immediately available funds to an account designated
                           by the Company as set forth on Schedule I hereto,
                           which funds will be delivered to the Company in
                           consideration of the Investor Shares issued at the
                           Closing.

          (b)  Deliveries by the Company. At the Closing, the Company shall
               deliver to the Investor the following:

                  (1)      the Investor Shares through The Depository Trust
                           Company DWAC system to the account that the Investor
                           has specified in writing to the Company; and

                  (2)      the Prospectus Supplement and the Prospectus.

4.  Representations, Warranties, Covenants and Agreements.

         (a)      Investor Representations, Warranties and Covenants. The
                  Investor represents, warrants and agrees as follows:

                  (1)      The Investor has received and reviewed copies of the
                           Registration Statement and the Prospectus, including
                           all documents incorporated by reference therein and
                           amendments thereto, and understands that no Person
                           has been authorized to give any information or to
                           make any representations that were not contained in
                           the Registration Statement and the Prospectus, and
                           the Investor has not relied on any such other
                           information or representations in making a decision
                           to purchase the Investor Shares. The Investor hereby
                           consents to receiving delivery of the Registration
                           Statement, the Prospectus and the Prospectus
                           Supplement, including all documents incorporated by
                           reference therein and amendments thereto, by
                           electronic mail. The Investor understands that an
                           investment in the Company involves a high degree of
                           risk for the reasons, among others, set forth under
                           the caption "RISK FACTORS" in the Prospectus and the
                           Prospectus Supplement and the documents incorporated
                           by reference in the Prospectus and the Prospectus
                           Supplement.

                  (2)      The Investor acknowledges that it has sole
                           responsibility for its own due diligence
                           investigation and its own investment decision, and
                           that in connection with its investigation of the
                           accuracy of the information contained or incorporated
                           by reference in the Registration Statement, the
                           Prospectus and the Prospectus Supplement and its
                           investment decision, the Investor has not relied on
                           any representation or information not set forth in
                           this Agreement, the Registration Statement, the
                           Prospectus or the Prospectus Supplement, on the
                           selling agent (William Blair & Company, L.L.C.) or
                           any Person affiliated with the selling agent, or on
                           the fact that any other Person has decided to invest
                           in the Offered Shares.

                  (3)      The execution and delivery of this Agreement by the
                           Investor and the performance of this Agreement and
                           the consummation by the Investor of the transactions
                           contemplated hereby have been duly authorized by all
                           necessary


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                           (corporate, in the case of a corporation) action of
                           the Investor, and this Agreement, when duly executed
                           and delivered by the Investor, will constitute a
                           valid and legally binding instrument, enforceable in
                           accordance with its terms against the Investor,
                           except as enforcement hereof may be limited by the
                           effect of any applicable bankruptcy, insolvency,
                           reorganization or similar laws or court decisions
                           affecting enforcement of creditors' rights generally
                           and except as enforcement hereof is subject to
                           general principles of equity (regardless of whether
                           enforcement is considered in a proceeding in equity
                           or at law).

                  (4)      No state, federal or foreign regulatory approvals,
                           permits, licenses or consents or other contractual or
                           legal obligations are required for the Investor to
                           enter into this Agreement or purchase the Investor
                           Shares.

(b)      Company Representations, Warranties and Covenants. The Company hereby
         represents, warrants and agrees as follows:

         (1)      The Company has been duly incorporated and is validly existing
                  as a corporation in good standing under the laws of the State
                  of California, with power and authority (corporate and other)
                  to own its properties and conduct its business as described in
                  the Prospectus, and has been duly qualified as a foreign
                  corporation for the transaction of business and is in good
                  standing under the laws of each other jurisdiction in which it
                  owns or leases properties or conducts any business so as to
                  require such qualification, except for such jurisdictions
                  wherein the failure to be so qualified and in good standing
                  would not individually or in the aggregate have a material
                  adverse effect on the business, results of operations or
                  financial condition of the Company and its subsidiaries taken
                  as a whole (a "Material Adverse Effect"); and each subsidiary
                  of the Company has been duly incorporated and is validly
                  existing as a corporation in good standing under the laws of
                  its jurisdiction of incorporation, with power and authority
                  (corporate and other) to own its properties and conduct its
                  business as described in the Prospectus, and has been duly
                  qualified as a foreign corporation for the transaction of
                  business and is in good standing under the laws of each other
                  jurisdiction in which it owns or leases properties or conducts
                  any business so as to require such qualification, except for
                  such jurisdictions wherein the failure to be so qualified and
                  in good standing would not individually or in the aggregate
                  have a Material Adverse Effect.

         (2)      The execution, delivery and performance of this Agreement by
                  the Company and the consummation by the Company of the
                  transactions contemplated hereby have been duly authorized by
                  all necessary corporate action of the Company and the
                  Agreement has been duly executed and delivered by the Company;
                  and this Agreement, when duly executed and delivered by the
                  Investor, will constitute a valid and legally binding
                  instrument of the Company enforceable in accordance with its
                  terms, except as enforcement hereof may be limited by the
                  effect of any applicable bankruptcy, insolvency,
                  reorganization or similar laws or court decisions affecting
                  enforcement of creditors' rights generally and except as
                  enforcement hereof is subject to general principles of equity
                  (regardless of whether enforcement is considered in a
                  proceeding in equity or at law).

         (3)      The Investor Shares have been duly authorized by the Company,
                  and when issued and delivered by the Company against payment
                  therefor as contemplated hereby, the Investor Shares will be
                  validly issued, fully paid and nonassessable,


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                  and will conform to the description of the Common Stock
                  contained in the Prospectus.

         (4)      The execution and delivery of this Agreement, the consummation
                  by the Company of the transactions herein contemplated and the
                  compliance by the Company with the terms hereof do not and
                  will not violate the Articles of Incorporation (as amended to
                  date) of the Company or the By-Laws (as amended to date) of
                  the Company, or result in a breach or violation of any of the
                  terms or provisions of, or constitute a default under, any
                  indenture, mortgage, deed of trust, loan agreement or other
                  agreement or instrument to which the Company or any of its
                  subsidiaries is a party or by which the Company or any of its
                  subsidiaries is bound or to which any of their properties or
                  assets are subject, or any applicable statute or any order,
                  judgment, decree, rule or regulation of any court or
                  governmental or regulatory agency or body having jurisdiction
                  over the Company or any of its subsidiaries or any of their
                  properties or assets, except where such breach, violation,
                  default or the failure to be in compliance would not
                  individually or in the aggregate have a Material Adverse
                  Effect or adversely affect the ability of the Company to
                  consummate the transactions contemplated hereby; and no
                  consent, approval, authorization, order, registration, filing
                  or qualification of or with any such court or governmental or
                  regulatory agency or body is required for the valid
                  authorization, execution, delivery and performance by the
                  Company of this Agreement, the issue of the Investor Shares or
                  the consummation by the Company of the other transactions
                  contemplated by this Agreement, except for such consents,
                  approvals, authorizations, registrations or qualifications as
                  may be required under federal or state securities or "blue
                  sky" laws or in connection with the listing of the Offered
                  Shares on the Nasdaq National Market.

         (5)      The Company meets the requirements for the use of Form S-3
                  under the Securities Act of 1933, as amended (the "Securities
                  Act"), for the primary issuance of securities. The
                  Registration Statement has been declared effective by the
                  Commission and at the time it became effective, and as of the
                  date hereof, the Registration Statement complied and complies
                  with Rule 415 under the Securities Act. No stop order
                  suspending the effectiveness of the Registration Statement has
                  been issued and no proceeding for that purpose has been
                  initiated or, to the Company's knowledge, threatened by the
                  Commission. On the effective date of the Registration
                  Statement, the Registration Statement and the Prospectus fully
                  conformed, and at the date of the Closing, the Registration
                  Statement and the Prospectus will fully conform, in all
                  material respects with the applicable provisions of the
                  Securities Act and the applicable rules and regulations of the
                  Commission thereunder; on the effective date of the
                  Registration Statement, the Registration Statement did not,
                  and at the date of the Closing, the Registration Statement
                  will not, contain an untrue statement of a material fact or
                  omit to state a material fact required to be stated therein or
                  necessary in order to make the statements therein not
                  misleading; on the effective date of the Registration
                  Statement, the Prospectus did not, and on the date the
                  Prospectus Supplement is filed with the Commission pursuant to
                  Rule 424(b) under the Securities Act and the date of the
                  Closing, the Prospectus will not, contain an untrue statement
                  of a material fact necessary in order to make the statements
                  therein, in the light of the circumstances under which they
                  were made, not misleading; and when filed with the Commission,
                  the documents incorporated by reference in the Registration
                  Statement and the Prospectus, taken as a whole, fully
                  conformed or will fully conform in all material respects



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                  with the applicable provisions of the Securities Exchange Act
                  of 1934, as amended (the "Exchange Act"), and the applicable
                  rules and regulations of the Commission thereunder.

         (6)      The consolidated financial statements and financial schedules
                  of the Company included or incorporated by reference in the
                  Registration Statement and the Prospectus have been prepared
                  in conformity with generally accepted accounting principles
                  (except, with respect to the unaudited consolidated financial
                  statements, for the footnotes and subject to customary audit
                  adjustments) applied on a consistent basis, are consistent in
                  all material respects with the books and records of the
                  Company, and accurately present in all material respects the
                  consolidated financial position, results of operations and
                  cash flow of the Company and its subsidiaries as of and for
                  the periods covered thereby.

         (7)      Neither the Company nor any of its subsidiaries has sustained
                  since the date of the latest audited financial statements
                  included or incorporated by reference in the Prospectus any
                  material loss or interference with its business from fire,
                  explosion, flood or other calamity, whether or not covered by
                  insurance, or from any labor dispute or court or governmental
                  action, order or decree, otherwise than as disclosed in or
                  contemplated by the Prospectus; and, since the respective
                  dates as of which information is given in the Registration
                  Statement and the Prospectus, there has not been any material
                  change in the capital stock or long-term debt of the Company
                  or any of its subsidiaries, the Company and its subsidiaries
                  have not incurred any material liabilities or obligations,
                  direct or contingent, nor entered into any material
                  transactions not in the ordinary course of business and there
                  has not been any material adverse change in or affecting the
                  general affairs, management, financial position, stockholders'
                  equity or results of operations of the Company and its
                  subsidiaries considered as a whole, otherwise than as
                  disclosed or incorporated by reference in or contemplated by
                  the Prospectus.

         (8)      Other than as set forth or incorporated by reference in the
                  Prospectus, there are no legal, governmental or regulatory
                  proceedings pending to which the Company or any of its
                  subsidiaries is a party or of which any material property of
                  the Company or any of its subsidiaries is the subject which,
                  taking into account the likelihood of the outcome, the damages
                  or other relief sought and other relevant factors, would
                  individually or in the aggregate reasonably be expected to
                  have a Material Adverse Effect or adversely affect the ability
                  of the Company to consummate the transactions contemplated
                  hereby; to the best of the Company's knowledge, no such
                  proceedings are threatened or contemplated by governmental or
                  regulatory authorities or threatened by others.

         (9)      The Company together with its subsidiaries owns and possesses
                  all right, title and interest in and to, or has duly licensed
                  from third parties, all patents, patent rights, trade secrets,
                  inventions, know-how, trademarks, trade names, copyrights,
                  service marks and other proprietary rights ("Intellectual
                  Property") material to the business of the Company and each of
                  its subsidiaries taken as a whole. Neither the Company nor any
                  of its subsidiaries has received any notice of infringement,
                  misappropriation or conflict from any third party as to such
                  that has not been resolved or disposed of and to the Company's
                  knowledge, neither the Company nor any of its subsidiaries has
                  infringed, misappropriated or otherwise conflicted with
                  Intellectual Property of any third parties, which


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                  infringement, misappropriation or conflict would individually
                  or in the aggregate have a Material Adverse Effect.

         (10)     The conduct of the business of the Company and each of its
                  subsidiaries is in compliance in all respects with applicable
                  federal, state, local and foreign laws and regulations, except
                  where the failure to be in compliance would not individually
                  or in the aggregate have a Material Adverse Effect.

         (11)     The Company is not, and does not intend to conduct its
                  business in a manner in which it would become, an "investment
                  company" as defined in Section 3(a) of the Investment Company
                  Act of 1940, as amended.

         (12)     The Investor shall have no obligation with respect to any fees
                  incurred by the Company or any other Person (other than the
                  Investor, if the Investor has agreed in writing to pay such
                  fees) or with respect to any claims made by or on behalf of
                  other Persons for fees or commissions payable by the Company
                  to any broker, financial advisor or consultant, finder,
                  selling agent, investment banker, bank or other Person, that
                  may be due in connection with the transactions contemplated by
                  this Agreement. The Company shall indemnify and hold harmless
                  the Investor, its employees, officers, directors, trustees,
                  partners, or any affiliate of the Investor, from and against
                  any losses, claims, damages, costs (including the costs of
                  preparation and reasonable attorney's fees) and expenses
                  suffered in respect of such claimed or existing fees incurred
                  by the Company or any other Person (other than the Investor,
                  if the Investor has agreed in writing to pay such fees), as
                  such fees and expenses are incurred.

         (13)     Neither the Company nor to the Company's knowledge, any other
                  Person acting on its behalf has provided the Investor or its
                  agents or counsel with any information that the Company
                  believes constitutes material, non-public information.

5.       Conditions. The obligation of the Investor to purchase and acquire the
         Investor Shares hereunder shall be subject to the condition that all
         representations and warranties and other statements of the Company
         shall be true and correct as of and on each of the date of this
         Agreement and the date of the Closing, the condition that the Company
         shall have performed all of its obligations hereunder theretofore to be
         performed, and the following additional conditions:

               (a)  The Prospectus Supplement shall have been filed with the
                    Commission pursuant to Rule 424(b) under the Securities Act
                    within the applicable time period prescribed for such
                    filing, no stop order suspending the effectiveness of the
                    Registration Statement or any part thereof shall have been
                    issued and no proceeding for that purpose shall have been
                    initiated or threatened by the Commission, and the Company
                    shall have delivered the Prospectus Supplement to the
                    Investor in accordance with the federal securities laws.

               (b)  The Company shall have secured the listing of the Offered
                    Shares on the Nasdaq National Market (subject to official
                    notice of issuance).

               (c)  The Company shall have performed all of its obligations set
                    forth in the Selling Agent Agreement, dated as of July 15,
                    2002, by and among the Company and William Blair & Company,
                    L.L.C., required to be performed by the Company thereunder
                    on or prior to the Closing.

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6.       Miscellaneous.

               (a)  Fees and Expenses. Each of the parties hereto shall be
                    responsible for their own expenses incurred in connection
                    with the transactions contemplated hereby.

               (b)  Binding Agreement; Assignment. This Agreement shall be
                    binding upon, and shall inure solely to the benefit of, each
                    of the parties hereto, and each of their respective heirs,
                    executors, administrators, successors and permitted assigns,
                    and no other person shall acquire or have any right under or
                    by virtue of this Agreement. The Investor may not assign any
                    of its rights or obligations hereunder to any other person
                    or entity without the prior written consent of the Company.

               (c)  Entire Agreement. This Agreement, including Schedule I
                    hereto, constitutes the entire agreement among the parties
                    hereto with respect to the subject matter hereof and may be
                    amended only by written execution by both parties. Upon
                    execution by the Company and the Investor, this Agreement
                    shall be binding on both parties hereto.

               (d)  Consent To Jurisdiction. THIS AGREEMENT SHALL BE ENFORCED,
                    GOVERNED AND CONSTRUED IN ALL RESPECTS IN ACCORDANCE WITH
                    THE LAWS OF THE STATE OF CALIFORNIA, WITHOUT GIVING EFFECT
                    TO ITS CONFLICTS OF LAWS PRINCIPLES. FURTHERMORE, THE
                    INVESTOR HEREBY IRREVOCABLY SUBMITS TO THE JURISDICTION OF
                    THE COURTS OF THE STATE OF CALIFORNIA AND THE UNITED STATES
                    OF AMERICA FOR THE DISTRICT OF CALIFORNIA IN ANY LEGAL
                    PROCEEDING ARISING OUT OF OR RELATING TO THIS AGREEMENT.

               (e)  Notices. All notices, requests, consents and other
                    communication hereunder shall be in writing, shall be mailed
                    by first class registered or certified mail, or nationally
                    recognized overnight express courier postage prepaid, and
                    shall be deemed given when so mailed and shall be delivered
                    as addressed as follows:

                    if to the Company, to:

                    Cepheid
                    904 Caribbean Drive
                    Sunnyvale, CA  94089

                    Attn: Chief Financial Officer

                    with a copy mailed to:

                    Doug Cogen, Esq.
                    Fenwick & West LLP
                    Embarcadero Center West
                    275 Battery Street
                    San Francisco, CA  94111

                    or to such other person at such other place as the Company
                    shall designate to the Investor in writing; and if to the
                    Investor, at its address as set forth at the end of this
                    Agreement, or at such other address or addresses as may have
                    been furnished to the Company in writing.

               (f)  Counterparts. This Agreement maybe executed in any number of
                    counterparts and by the parties hereto in separate
                    counterparts, each of which when so executed shall be deemed

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                    to be an original and all of which taken together shall
                    constitute one in the same agreement.



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         IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first above written.

                            Cepheid

                            By:
                                 --------------------------------------------
                                 Name:
                                 Title:

Accepted and agreed to as of the date first above written:


- -----------------------------------------------------
Name of Investor (Print)

By:
     ------------------------------------------------
     Name:
     Title
     Address:
               --------------------------------------
               --------------------------------------


Telephone:
           ------------------------------------------
Facsimile:
           ------------------------------------------
Nominee (name in which Investor Shares are
to be registered, if different than name of
Investor)
          -------------------------------------------

Address of Nominee:

- --------------------------------------

- --------------------------------------
Taxpayer ID. Number:
(if acquired in the name of a nominee, the
taxpayer ID. number of such nominee)

DTC account number:

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                                   SCHEDULE I

                                       TO

                            STOCK PURCHASE AGREEMENT

Name of Investor:


Number of Offered Shares to be Purchased by Investor:


Per Share Purchase Price:


Aggregate Purchase Price:


Date of Closing:




WIRE INSTRUCTIONS

Aggregate Purchase Price to be wired to:

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