<PAGE>

                                                                   EXHIBIT 10.27


                                    EXHIBIT H

                            STOCK PURCHASE AGREEMENT

                         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

<PAGE>

               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

<PAGE>

               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.

<PAGE>

        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.

<PAGE>

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

<PAGE>

               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.

<PAGE>

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

<PAGE>

               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.

<PAGE>

               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.

<PAGE>

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