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                                                                     EXHIBIT 4.1




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                         COMMON STOCK PURCHASE AGREEMENT

        THIS COMMON STOCK PURCHASE AGREEMENT (the "AGREEMENT") is made and
entered into as of March 5, 2002, by and between Geron Corporation, a Delaware
corporation having its principal place of business at 230 Constitution Drive,
Menlo Park, California 94025 (the "COMPANY"), and Lynx Therapeutics, Inc., a
Delaware corporation having its principal place of business at 25861 Industrial
Boulevard, Hayward, CA 94545 (the "ACQUIRER").

        A.      The Company has agreed to issue 210,000 shares of the Company's
                common stock, par value $.001 per share (the "COMMON STOCK") to
                Acquirer pursuant to that certain Purchase Agreement between the
                Company and Acquirer dated as of March 5, 2002 (the "PURCHASE
                AGREEMENT").

        B.      The Acquirer and the Company desire to specify the terms and
                conditions of the Company's issuance of such common stock.

                THE PARTIES AGREE AS FOLLOWS:

1.      ISSUANCE OF SHARES; PURCHASE PRICE. The Acquirer hereby acquires and the
        Company hereby issues to Acquirer 210,000 shares (the "SHARES") of
        Common Stock in consideration of the license granted pursuant to that
        certain License Agreement between the Company and the Acquirer dated as
        of March 5, 2002.

2.      CLOSING; DELIVERY. The consummation of the transaction contemplated by
        this Agreement (the "CLOSING") shall be held on the date hereof
        ("CLOSING DATE"). The Closing shall be held at the offices of the
        Company or at such other time or place as Acquirer and the Company may
        mutually agree. At the Closing, the Company shall deliver to the
        Acquirer a stock certificate, in the name of the Acquirer, representing
        the Shares against delivery of the Patent Assignment (as defined in the
        Purchase Agreement).

3.      CLOSING CONDITIONS.

        3.1     The Company's respective obligations to issue and deliver the
                stock certificate representing the Shares to the Acquirer shall
                be subject to the following condition, which may be waived by
                the Company:

                3.1.1   the execution of the Purchase Agreement; and

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        3.1.2   the accuracy of the representations and warranties made by the
                Acquirer shall be true and correct in all material respects as
                of the Closing Date.

    3.2 The Acquirer's obligation to accept delivery of the stock certificate
        representing the Shares shall be subject to the following conditions,
        any one or more of which may be waived the Acquirer:

        3.2.1   the execution of the Purchase Agreement;

        3.2.2   the covenants and obligations that the Company is required to
                perform or to comply with pursuant to this Agreement, at or
                prior to the Closing, must have been duly performed and complied
                with in all material respects;

        3.2.3   the Company shall have available under its Certificate of
                Incorporation sufficient authorized shares of capital stock to
                issue and sell the Shares to Acquirer; and

        3.2.4   the accuracy of the representations and warranties made by the
                Company shall be true and correct in all material respects as of
                the Closing Date.

4. RESTRICTIONS ON RESALE OF SHARES.

   4.1  Legends. The Acquirer understands and acknowledges that the Shares are
        not registered under the Securities Act of 1933 (the "ACT") and that
        under the Act and other applicable laws the Acquirer may be required to
        hold such Shares for an indefinite period of time. Each stock
        certificate representing Shares shall bear the following legends:

        "THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE
        SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"). ANY TRANSFER OF SUCH
        SECURITIES SHALL BE INVALID UNLESS A REGISTRATION STATEMENT UNDER THE
        ACT IS IN EFFECT AS TO SUCH TRANSFER OR, IN THE OPINION OF COUNSEL
        REASONABLY ACCEPTABLE TO THE COMPANY, SUCH REGISTRATION IS UNNECESSARY
        FOR SUCH TRANSFER TO COMPLY WITH THE ACT.

        THE SECURITIES REPRESENTED HEREBY ARE SUBJECT TO THE TERMS OF THE COMMON
        STOCK PURCHASE AGREEMENT, DATED MARCH 5, 2002. A COPY OF THE AGREEMENT
        CAN BE OBTAINED FROM THE SECRETARY OF THE COMPANY."

5. REGISTRATION RIGHTS

   5.1  The Company agrees to prepare and file with the Securities and Exchange
        Commission ("COMMISSION"), on or before March 8, 2002, a registration
        statement under the Act (the "REGISTRATION STATEMENT"), on Form S-3 or
        other appropriate form, so as to permit a non-underwritten public
        offering and resale of

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        the Shares under the Act by the Acquirer. The Company agrees to
        diligently pursue making that registration statement effective as soon
        as practicable following the execution of this Agreement. The Company
        will notify the Acquirer of the effectiveness of the Registration
        Statement within one business day of receiving notice from the
        Commission.

   5.2  The Company will prepare and file with the Commission such amendments
        and supplements to the Registration Statement and the prospectus as may
        be necessary to keep the Registration Statement or post-effective
        amendment filed under this Section 5 effective under the Act until the
        earlier of (i) the date that none of the Shares covered by such
        Registration Statement are outstanding, (ii) the date that all of the
        Shares have been sold pursuant to such Registration Statement, (iii) the
        date the Acquirer receives an opinion of counsel to the Company, which
        counsel shall be reasonably acceptable to the Acquirer, that the Shares
        may be sold under the provisions of Rule 144 without limitation as to
        volume, (iv) the date that all Shares have been otherwise transferred to
        persons who may trade such shares without restriction under the Act, and
        the Company has delivered a new certificate or other evidence of
        ownership for such securities not bearing a restrictive legend, or (v)
        the date all Shares may be sold at any time, without volume or manner of
        sale limitations pursuant to Rule 144(k) or any similar provision then
        in effect under the Act in the opinion of counsel to the Company, which
        counsel shall be reasonably acceptable to the Acquirer (the
        "EFFECTIVENESS PERIOD").

   5.3  The Company shall furnish to the Acquirer with respect to the Shares
        registered under the Registration Statement such reasonable number of
        copies of the Registration Statement, prospectuses and preliminary
        prospectuses in conformity with the requirements of the Act and such
        other documents as the Acquirer may reasonably request, in order to
        facilitate the public sale or other disposition of all or any of the
        Shares by the Acquirer, provided, however, that the obligation of the
        Company to deliver copies of prospectuses or preliminary prospectuses to
        the Acquirer shall be subject to the receipt by the Company of
        reasonable assurances from the Acquirer that the Acquirer will comply
        with the applicable provisions of the Act and of such other securities
        or blue sky laws as may be applicable in connection with any use of such
        prospectuses or preliminary prospectuses.

   5.4  All fees, disbursements and out-of-pocket expenses and costs incurred by
        the Company in connection with the preparation and filing of the
        Registration Statement and any post-effective amendments thereto under
        this Section 5 and in complying with applicable securities and Blue Sky
        laws (including, without limitation, all attorneys' fees of the Company)
        shall be borne by the Company. The Acquirer shall bear the cost of
        underwriting and/or brokerage discounts, fees and commissions, if any,
        applicable to the Shares being registered and the fees and expenses of
        their counsel. The Company at its expense will supply the Acquirer with
        copies of the applicable Registration Statement and the prospectus
        included therein and other related documents in such quantities as may
        be reasonably requested by the Acquirer.

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   5.5  The Company will advise the Acquirer, promptly after it shall receive
        notice or obtain knowledge of the issuance of any stop order by the
        Commission delaying or suspending the effectiveness of the Registration
        Statement or of the initiation of any proceeding for that purpose, that
        the Company will use its commercially reasonable efforts to prevent the
        issuance of any stop order or to obtain its withdrawal at the earliest
        possible moment if such stop order should be issued.

   5.6  With a view to making available to the Acquirer the benefits of Rule 144
        (or its successor rule) and any other rule or regulation of the
        Commission that may at any time permit the Acquirer to sell the
        Securities to the public without registration, the Company covenants and
        agrees to: (i) make and keep public information available, as those
        terms are understood and defined in Rule 144, until the earlier of (A)
        such date as all of the Shares may be resold pursuant to Rule 144(k) or
        any other rule of similar effect or (B) such date as all of the Shares
        shall have been resold; and (ii) file with the Commission in a timely
        manner all reports and other documents required of the Company under the
        Act and under the Exchange Act of 1934, as amended.

   5.7  The Acquirer will cooperate with the Company in all respects in
        connection with this Agreement, including timely supplying all
        information reasonably requested by the Company (which shall include all
        information regarding the Acquirer and proposed manner of sale of the
        Shares required to be disclosed in any Registration Statement) and
        executing and returning all documents reasonably requested in connection
        with the registration and sale of the Shares and entering into and
        performing their obligations under any underwriting agreement, if the
        offering is an underwritten offering, in usual and customary form, with
        the managing underwriter or underwriters of such underwritten offering.
        Nothing in this Agreement shall obligate the Acquirer to consent to be
        named as an underwriter in any Registration Statement.


   5.8  If the Registration Statement has not been declared effective by the
        Commission on or before April 30, 2002 (the "OPTION DATE"), then the
        Acquirer shall have the option to return for cancellation (the
        "CANCELLATION OPTION") all of the Shares to the Company. As
        consideration for the return of the Shares to the Company for
        cancellation, the Company shall pay to Acquirer an amount equal to One
        Million Five Hundred Thousand Dollars ($1,500,000), payable in
        immediately available funds. The Acquirer shall not be required to make
        any representations or warranties with respect to the Shares, except
        with respect to its ownership of the Shares. At anytime following the
        Option Date, the Acquirer may exercise the Cancellation Option by
        delivering written notice to the Company that states that it has elected
        to exercise the Cancellation Option (the "CANCELLATION OPTION EXERCISE
        NOTICE"). If the Cancellation Option Notice is not received by the
        Company within thirty (30) days following the Option Date, then the
        Cancellation Option shall expire and be of no further force or effect.
        This Cancellation Option shall not be enforceable by any transferee of
        the Shares held by the Acquirer.






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6. INDEMNIFICATION.

For the purpose of this Section 6:

the term "REGISTRATION STATEMENT" shall include any final prospectus, exhibit,
supplement or amendment included in or relating to the Registration Statement
referred to in Section 5.1; and the term "UNTRUE STATEMENT" shall include any
untrue statement or alleged untrue statement, or any omission or alleged
omission to state in the Registration Statement a material fact required to be
stated therein or necessary to make the statements therein, in the light of the
circumstances under which they were made, not misleading.

   6.1  The Company agrees to indemnify and hold harmless the Acquirer from and
        against any losses, claims, damages or liabilities to which the Acquirer
        may become subject (under the Act or otherwise) insofar as such losses,
        claims, damages or liabilities (or actions or proceedings in respect
        thereof) arise out of, or are based upon (i) any untrue statement of a
        material fact contained in the Registration Statement, (ii) any omission
        of a material fact required to be stated in the Registration Statement
        or necessary in order to make the statements in the Registration
        Statement not misleading or (iii) any failure by the Company to fulfill
        any undertaking included in the Registration Statement, and the Company
        will reimburse the Acquirer for any reasonable legal or other expenses
        reasonably incurred in investigating, defending or preparing to defend
        any such action, proceeding or claim, provided, however, that the
        Company shall not be liable in any such case to the extent that such
        loss, claim, damage or liability arises out of, or is based upon, an
        untrue statement made in such Registration Statement in reliance upon
        and in conformity with written information furnished to the Company by
        or on behalf of the Acquirer specifically for use in preparation of the
        Registration Statement or the failure of the Acquirer to comply with its
        covenants and agreements contained in Sections 8.1 or 8.5.2 hereof or
        any misstatement or omission in any prospectus that is corrected in any
        subsequent prospectus that was delivered to the Acquirer prior to the
        pertinent sale or sales by the Acquirer.

   6.2  The Acquirer agrees to indemnify and hold harmless the Company (and each
        person, if any, who controls the Company within the meaning of Section
        15 of the Act, each officer of the Company who signs the Registration
        Statement and each director of the Company) from and against any losses,
        claims, damages or liabilities to which the Company (or any such
        officer, director or controlling person) may become subject (under the
        Act or otherwise), insofar as such losses, claims, damages or
        liabilities (or actions or proceedings in respect thereof) arise out of,
        or are based upon, (i) any failure to comply with the covenants and
        agreements contained in Sections 8.1 or 8.5.2 hereof or (ii) any untrue
        statement of a material fact contained in the Registration Statement or
        any omission of a material fact required to be stated in the
        Registration Statement or necessary in order to make the statements in
        the Registration Statement not misleading if such untrue statement or
        omission was made in reliance upon and in conformity with written
        information furnished to the Company by or on behalf of the Acquirer
        specifically for use in preparation of the Registration Statement, and
        the Acquirer

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        will reimburse the Company (or such officer, director or controlling
        person), as the case may be, for any legal or other expenses reasonably
        incurred in investigating, defending or preparing to defend any such
        action, proceeding or claim; provided, however, that the Acquirer shall
        not be liable in any such case for (A) any untrue statement or omission
        in the Registration Statement, prospectus, or other such document which
        statement is corrected by the Acquirer and delivered to the Company
        prior to the sale from which such loss occurred, (B) any untrue
        statement or omission in any prospectus which is corrected by the
        Acquirer in any subsequent prospectus, or supplement or amendment
        thereto, and delivered to the Company prior to the sale or sales from
        which a loss or liability arose, or (C) any failure by the Company to
        fulfill any of its obligations under Section 6.1 hereof.

   6.3  Promptly after receipt by any indemnified person of a notice of a claim
        or the beginning of any action in respect of which indemnity is to be
        sought against an indemnifying person pursuant to this Section 6, such
        indemnified person shall notify the indemnifying person in writing of
        such claim or of the commencement of such action, but the omission to so
        notify the indemnifying party will not relieve it from any liability
        which it may have to any indemnified party under this Section 6 (except
        to the extent that such omission materially and adversely affects the
        indemnifying party's ability to defend such action) or from any
        liability otherwise than under this Section 6. Subject to the provisions
        hereinafter stated, in case any such action shall be brought against an
        indemnified person, the indemnifying person shall be entitled to
        participate therein, and, to the extent that it shall elect by written
        notice delivered to the indemnified party promptly after receiving the
        aforesaid notice from such indemnified party, shall be entitled to
        assume the defense thereof, with counsel reasonably satisfactory to such
        indemnified person. After notice from the indemnifying person to such
        indemnified person of its election to assume the defense thereof, such
        indemnifying person shall not be liable to such indemnified person for
        any legal expenses subsequently incurred by such indemnified person in
        connection with the defense thereof, provided, however, that if there
        exists or shall exist a conflict of interest that would make it
        inappropriate, in the reasonable opinion of counsel to the indemnified
        person, for the same counsel to represent both the indemnified person
        and such indemnifying person or any affiliate or associate thereof, the
        indemnified person shall be entitled to retain its own counsel at the
        expense of such indemnifying person; provided, however, that no
        indemnifying person shall be responsible for the fees and expenses of
        more than one separate counsel (together with appropriate local counsel)
        for all indemnified parties. In no event shall any indemnifying person
        be liable in respect of any amounts paid in settlement of any action
        unless the indemnifying person shall have approved the terms of such
        settlement. No indemnifying person shall, without the prior written
        consent of the indemnified person, effect any settlement of any pending
        or threatened proceeding in respect of which any indemnified person is
        or could have been a party and indemnification could have been sought
        hereunder by such indemnified person, unless such settlement includes an
        unconditional release of such indemnified person from all liability on
        claims that are the subject matter of such proceeding.

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7. REPRESENTATIONS AND ACKNOWLEDGMENTS OF THE COMPANY.

The Company hereby represents, warrants and covenants to the Acquirer as
follows:

   7.1  Organization, Good Standing and Qualification. The Company is a
        corporation duly organized, validly existing and in good standing under
        the laws of the State of Delaware and has all requisite corporate power
        and authority to carry on its business as now conducted and as presently
        proposed to be conducted. The Company is duly qualified to transact
        business and is in good standing as a foreign corporation in each
        jurisdiction in which the failure to so qualify would have a material
        adverse effect on its business or properties.

   7.2  Authorization. All corporate action on the part of Company, its
        officers, directors and stockholders necessary for the authorization,
        execution and delivery of this Agreement, the performance of all
        obligations of Company hereunder and the authorization, issuance and
        delivery of the Shares has been taken or will be taken prior to the
        Closing, and this Agreement, when executed and delivered will constitute
        valid and legally binding obligations of the Company, enforceable
        against the Company in accordance with their terms, except as limited by
        applicable bankruptcy, insolvency, reorganization, moratorium,
        fraudulent conveyance and other laws of general application affecting
        enforcement of creditors' rights generally, as limited by laws relating
        to the availability of specific performance, injunctive relief or other
        equitable remedies.

   7.3  Valid Issuance of Common Stock. The Shares that are being purchased by
        Acquirer hereunder, when issued, sold and delivered in accordance with
        the terms hereof for the consideration expressed herein, will be duly
        and validly authorized and issued, fully paid and nonassessable and free
        of restrictions on transfer other than restrictions on transfer under
        this Agreement and applicable state and federal securities laws.

   7.4  Legal Proceedings and Orders. There is no action, suit, proceeding or
        investigation pending or threatened against the Company that questions
        the validity of this Agreement or the right of the Company to enter into
        this Agreement or to consummate the transactions contemplated hereby,
        nor is the Company aware of any basis for any of the forgoing. The
        Company is neither a party nor subject to the provisions of any order,
        writ, injunction, judgment or decree of any court or government agency
        or instrumentality that would affect the ability of the Company to enter
        into this Agreement or to consummate the transactions contemplated
        hereby.

8. REPRESENTATIONS AND ACKNOWLEDGMENTS OF THE ACQUIRER.

The Acquirer hereby represents, warrants, acknowledges and agrees that:

   8.1  Investment. The Acquirer is acquiring the Shares for the Acquirer's own
        account, and not directly or indirectly for the account of any other
        person. The Acquirer is acquiring the Shares for investment and not with
        a view to distribution or resale

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        thereof except in compliance with the Act and any applicable state law
        regulating securities.

   8.2  Access to Information. Acquirer has consulted with its own attorney,
        accountant, or investment advisor as the Acquirer has deemed advisable
        with respect to the investment and has determined its suitability for
        Acquirer. The Acquirer has had the opportunity to ask questions of, and
        to receive answers from, appropriate executive officers of the Company
        with respect to the terms and conditions of the transactions
        contemplated hereby and with respect to the business, affairs, financial
        condition and results of operations of the Company. The Acquirer has had
        access to such financial and other information as is necessary in order
        for the Acquirer to make a fully informed decision as to investment in
        the Company, and has had the opportunity to obtain any additional
        information necessary to verify any of such information to which the
        Acquirer has had access. Acquirer acknowledges that neither the Company
        nor any of its officers, directors, employees, agents, representatives,
        or advisors have made any representation or warranty.

   8.3  Business and Financial Expertise. The Acquirer further represents and
        warrants that it has such business or financial expertise as to be able
        to evaluate its investment in the Company and purchase of the Shares.

   8.4  Speculative Investment. The Acquirer acknowledges that the investment in
        the Company represented by the Shares is highly speculative in nature
        and is subject to a high degree of risk of loss in whole or in part; the
        amount of such investment is within the Acquirer's risk capital means
        and is not so great in relation to the Acquirer's total financial
        resources as would jeopardize the personal financial needs of the
        Acquirer in the event such investment were lost in whole or in part.

   8.5  Unregistered Securities. Acquirer acknowledges that:

        8.5.1   The Acquirer must bear the economic risk of investment for an
                indefinite period of time because the Shares have not been
                registered under the Act and therefore cannot and will not be
                sold unless they are subsequently registered under the Act or an
                exemption from such registration is available. The Company has
                made no agreements, covenants or undertakings whatsoever to
                register any of the Shares under the Act, except as provided in
                Section 5 above. The Company has made no representations,
                warranties or covenants whatsoever as to whether any exemption
                from the Act, including, without limitation, any exemption for
                limited sales in routine brokers' transactions pursuant to Rule
                144 under the Act, will become available and any such exemption
                pursuant to Rule 144, if available at all, will not be available
                unless: (i) a public trading market then exists in the Company's
                common stock, (ii) the Company has complied with the information
                requirements of Rule 144, and (iii) all other terms and
                conditions of Rule 144 have been satisfied.

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        8.5.2   Transfer of the Shares has not been registered or qualified
                under any applicable state law regulating securities and,
                therefore, the Shares cannot and will not be sold unless they
                are subsequently registered or qualified under any such act or
                an exemption therefrom is available. The Company has made no
                agreements, covenants or undertakings whatsoever to register or
                qualify any of the Shares under any such act, except as provided
                in Section 5 above. The Company has made no representations,
                warranties or covenants whatsoever as to whether any exemption
                from any such act will become available.

        8.5.3   The Acquirer hereby certifies that it is an "accredited
                investor" as that term is defined in Rule 501 under the Act.

9.      TAX ADVICE. The Acquirer acknowledges that the Acquirer has not relied
        and will not rely upon the Company or the Company's counsel with respect
        to any tax consequences related to the ownership, purchase, or
        disposition of the shares. The Acquirer assumes full responsibility for
        all such consequences and for the preparation and filing of all tax
        returns and elections which may or must be filed in connection with such
        shares.

10.     NOTICES. Any notice or other communication required or permitted
        hereunder shall be in writing and shall be deemed to have been duly
        given on the date of service if served personally or five days, not
        including Saturdays, Sundays, or national holidays, after mailing if
        mailed by first class United States mail, certified or registered with
        return receipt requested, postage prepaid, and addressed as follows:

        To the Company at:              Geron Corporation
                                        230 Constitution Drive
                                        Menlo Park, California  94025
                                        Attention: Chief Financial Officer
                                        Telephone:    (650) 473-7700
                                        Facsimile:    (650) 473-7750


        To the Acquirer at:             Lynx Therapeutics, Inc.
                                        25861 Industrial Boulevard
                                        Hayward, CA 94545
                                        Attention:  Chief Financial Officer
                                        Telephone:    (510)670-9300
                                        Facsimile:    (510)670-9303


11.     BINDING EFFECT. This Agreement shall be binding upon the heirs, legal
        representatives and successors of the Company and of the Acquirer;
        provided, however, that the Acquirer may not assign any rights or
        obligations under this Agreement. The Company's rights under this
        Agreement shall be freely assignable.

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12.     GOVERNING LAW. This Agreement shall be governed by and construed in
        accordance with the laws of the State of California.

13.     ENTIRE AGREEMENT. This Agreement constitutes the entire agreement of the
        parties pertaining to the Shares and supersedes all prior and
        contemporaneous agreements, representations, and understandings of the
        parties.



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

                                        GERON CORPORATION

                                        /s/ David L. Greenwood
                                        ----------------------------------------
                                        By:    David L. Greenwood
                                        Title: Chief Financial Officer and
                                               Senior Vice President,
                                               Corporate Development


                                        LYNX THERAPEUTICS, INC.

                                        /s/ Norman J.W. Russell
                                        ---------------------------------------
                                        By:    Norman J.W. Russell
                                        Title: President and Chief Executive
                                               Officer

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