<PAGE>   1

                                                                     EXHIBIT 4.2


                                                                       EXHIBIT C
                                                                              TO
                                                                      SECURITIES
                                                                        PURCHASE
                                                                       AGREEMENT

                          REGISTRATION RIGHTS AGREEMENT

         REGISTRATION RIGHTS AGREEMENT (this "AGREEMENT"), dated as of June 29,
2000, by and between Geron Corporation, a Delaware corporation, with its
headquarters located at 230 Constitution Drive, Menlo Park, California 94025
(the "COMPANY"), and the undersigned (together with its affiliates, the "INITIAL
INVESTOR").

         WHEREAS:

         A. In connection with the Securities Purchase Agreement by and among
the parties hereto of even date herewith (the "SECURITIES PURCHASE AGREEMENT"),
the Company has agreed, upon the terms and subject to the conditions contained
therein, to issue and sell to the Initial Investor (i) convertible debentures
(the "DEBENTURES") that are convertible into shares of the Company's common
stock (the "COMMON STOCK"), upon the terms and subject to the limitations and
conditions set forth in such Debentures and (ii) warrants (the "WARRANTS") to
acquire 834,836 shares of Common Stock, upon the terms and conditions and
subject to the limitations and conditions set forth in the Stock Purchase
Warrant dated June 29, 2000; and

         B. To induce the Initial Investor to execute and deliver the Securities
Purchase Agreement, the Company has agreed to provide certain registration
rights under the Securities Act of 1933, as amended, and the rules and
regulations thereunder, or any similar successor statute (collectively, the
"1933 ACT"), and applicable state securities laws;

         NOW, THEREFORE, in consideration of the premises and the mutual
covenants contained herein and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the Company and the
Initial Investor hereby agree as follows:

<PAGE>   2

         1. DEFINITIONS.

                  a. As used in this Agreement, the following terms shall have
the following meanings:

                           (i) "INVESTORS" means the Initial Investor and any
transferee or assignee who agrees to become bound by the provisions of this
Agreement in accordance with Section 9 hereof.

                           (ii) "REGISTER," "REGISTERED," and "REGISTRATION"
refer to a registration effected by preparing and filing a Registration
Statement or Statements in compliance with the 1933 Act and pursuant to Rule 415
under the 1933 Act or any successor rule providing for offering securities on a
continuous basis ("RULE 415"), and the declaration or ordering of effectiveness
of such Registration Statement by the United States Securities and Exchange
Commission (the "SEC").

                           (iii) "REGISTRABLE SECURITIES" means (A) the
Debenture Shares (as defined in the Securities Purchase Agreement) issued or
issuable upon conversion or otherwise pursuant to the Debentures (including,
without limitation, shares of Common Stock issued or issuable in respect of
interest or in redemption of the Debentures in accordance with the terms of the
Debentures and Section 2(c) herein); (B) the Warrant Shares (as defined in the
Securities Purchase Agreement) issued or issuable upon exercise of or otherwise
pursuant to the Warrants; and (C) any shares of capital stock issued or issuable
as a dividend on or in exchange for or otherwise with respect to any of the
foregoing.

                           (iv) "REGISTRATION STATEMENT(S)" means a registration
statement(s) of the Company under the 1933 Act.

                  b. Capitalized terms used herein and not otherwise defined
herein shall have the respective meanings set forth in the Securities Purchase
Agreement.


         2. REGISTRATION.

                  a. MANDATORY REGISTRATION. The Company shall prepare, and, on
or prior to the date (the "FILING DATE") which is twenty (20) business days
after the date of the Closing under the Securities Purchase Agreement (the
"CLOSING DATE"), file with the SEC a Registration Statement on Form S-3 (or, if
Form S-3 is not then available, on such form of Registration Statement as is
then available to effect a registration of the Registrable Securities, subject
to the consent of the Initial Investor, which consent will not be unreasonably
withheld) covering the resale of the Registrable Securities, which Registration
Statement, to the extent allowable under the 1933 Act and the rules and
regulations promulgated thereunder (including Rule 416), shall state that such
Registration Statement also covers such indeterminate number of additional
shares of Common Stock as may become issuable upon conversion of the Debentures
and exercise of the Warrants to prevent dilution resulting from stock splits,
stock dividends or similar transactions. The number of shares of


                                     - 2 -
<PAGE>   3

Common Stock initially included in such Registration Statement shall be no less
than 125% of the sum of the number of Debenture Shares and Warrant Shares that
are then issuable upon conversion of the Debentures (based on the Conversion
Price as would then be in effect) and the exercise of the Warrants, without
regard to any limitation on the Investor's ability to convert the Debentures or
exercise the Warrants. The Company acknowledges that the number of shares
initially included in the Registration Statement represents a good faith
estimate of the maximum number of shares issuable upon conversion of the
Debentures and exercise of the Warrants. The Registration Statement (and each
amendment or supplement thereto, and each request for acceleration of
effectiveness thereof) shall be provided to (and subject to the reasonable
approval of) the Initial Investor and its counsel prior to its filing or other
submission.

                  b. UNDERWRITTEN OFFERING. [Intentionally omitted].

                  c. PAYMENTS BY THE COMPANY. The Company shall use its best
efforts to obtain effectiveness of the Registration Statement as soon as
practicable but in any event not later than one hundred fifty (150) days after
the Closing Date (the "REGISTRATION DEADLINE"). If (i) the Registration
Statement(s) covering the Registrable Securities required to be filed by the
Company pursuant to Section 2(a) hereof is not declared effective by the
Registration Deadline, or (ii) after the Registration Statement has been
declared effective by the SEC, sales of all of the Registrable Securities cannot
be made pursuant to the Registration Statement, or (iii) the Common Stock is not
listed or included for quotation on the Nasdaq National Market ("NASDAQ"), the
Nasdaq SmallCap Market ("NASDAQ SMALLCAP"), the New York Stock Exchange (the
"NYSE") or the American Stock Exchange (the "AMEX") after being so listed or
included for quotation, then the Company will make payments to the Investors in
such amounts and at such times as shall be determined pursuant to this Section
2(c) as partial relief for the damages to the Investors by reason of any such
delay in or reduction of their ability to sell the Registrable Securities (which
remedy shall not be exclusive of any other remedies available at law or in
equity). The Company shall pay to each holder of the Debentures or Registerable
Securities an amount equal to the then outstanding principal amount of the
Debentures (and, in the case of holders of Registrable Securities, the principal
amount of Debentures from which such Registrable Securities were converted)
("OUTSTANDING PRINCIPAL AMOUNT"), multiplied by the Applicable Percentage (as
defined below), multiplied by the sum of: (i) the number of months (prorated for
partial months) after the Registration Deadline and prior to the date the
Registration Statement is declared effective by the SEC; provided, however, that
there shall be excluded from such period any delays which are solely
attributable to changes required by the Investors in the Registration Statement
with respect to information relating to the Investors, including, without
limitation, changes to the plan of distribution, or to the failure of the
Investors to conduct their review of the Registration Statement pursuant to
Section 3(h) below in a reasonably prompt manner or to provide information in
accordance with Section 4(a) below; (ii) the number of months (prorated for
partial months) during the Registration Period (as defined below) that sales of
all of the Registrable Securities cannot be made pursuant to the Registration
Statement after the Registration Statement has been declared effective
(including, without limitation, when sales cannot be made by reason of the
Company's failure to properly supplement or amend the prospectus included
therein in accordance with the terms of this Agreement (including Section 3(b)
hereof or otherwise), but excluding any days during an Allowed Delay (as defined
in Section 3(f)); and (iii) the number of months (prorated for partial months)
that the Common Stock is not listed or included


                                     - 3 -
<PAGE>   4

for quotation on the Nasdaq, Nasdaq SmallCap, NYSE or AMEX or that trading
thereon is halted after the Registration Statement has been declared effective.
The term "APPLICABLE PERCENTAGE" means two hundredths (.020). (For example, if
the Registration Statement becomes effective one (1) month after the
Registration Deadline, the Company would pay $20,000 for each $1,000,000 of
Outstanding Principal Amount. If thereafter, sales could not be made pursuant to
the Registration Statement for an additional period of one (1) month, the
Company would pay an additional $20,000 for each $1,000,000 of Outstanding
Principal Amount.) Such amounts shall be paid in cash; provided, however, that
if such amounts are not paid to the Investors by the Payment Deadline (as
defined below), at each Investor's option, such amounts may be added to the
principal amount of the Debentures and thereafter be convertible into Common
Stock at the "CONVERSION PRICE" (as defined in the Debentures) in accordance
with the terms of the Debentures. Any shares of Common Stock issued upon
conversion of such amounts shall be Registrable Securities. If the Investor
desires to convert the amounts due hereunder into Registrable Securities, it
shall so notify the Company in writing within two (2) business days of the
Payment Deadline (as defined below) and such amounts shall be so convertible
(pursuant to the mechanics set forth under the Debentures), beginning upon the
expiration of the Payment Deadline (as defined below) for which the cash amount
would otherwise be due in accordance with the following sentence. Payments of
cash pursuant hereto shall be made within five (5) days after the end of each
period that gives rise to such obligation (the "PAYMENT DEADLINE"), provided
that, if any such period extends for more than thirty (30) days, interim
payments shall be made for each such thirty (30) day period.

                  d. PIGGY-BACK REGISTRATIONS. Subject to the last sentence of
this Section 2(d), if at any time prior to the expiration of the Registration
Period (as hereinafter defined) the Company shall determine to file with the SEC
a Registration Statement relating to an offering for its own account or the
account of others under the 1933 Act of any of its equity securities (other than
on Form S-4 or Form S-8 or their then equivalents relating to equity securities
to be issued solely in connection with any acquisition of any entity or business
or equity securities issuable in connection with stock option or other employee
benefit plans), the Company shall send to any party who is entitled to
registration rights under this Section 2(d) written notice of such determination
and, if within fifteen (15) days after the effective date of such notice, such
Investor shall so request in writing, the Company shall include in such
Registration Statement all or any part of the Registrable Securities such
Investor requests to be registered, except that if, in connection with any
underwritten public offering for the account of the Company the managing
underwriter(s) thereof shall impose a limitation on the number of shares of
Common Stock which may be included in the Registration Statement because, in
such underwriter(s)' judgment, marketing or other factors dictate such
limitation is necessary to facilitate public distribution, then the Company
shall be obligated to include in such Registration Statement only such limited
portion of the Registrable Securities with respect to which such Investor has
requested inclusion hereunder as the underwriter shall permit. Any exclusion of
Registrable Securities shall be made pro rata among the Investors seeking to
include Registrable Securities in proportion to the number of Registrable
Securities sought to be included by such Investors; provided, however, that the
Company shall not exclude any Registrable Securities unless the Company has
first excluded all outstanding securities, the holders of which are not entitled
by contract to inclusion of such securities in such Registration Statement or
are not entitled to pro rata inclusion with the Registrable Securities; and
provided, further, however, that, after giving effect to the immediately
preceding proviso, any exclusion of Registrable Securities


                                     - 4 -
<PAGE>   5

shall be made pro rata with holders of other securities having the contractual
right to include such securities in the Registration Statement other than
holders of securities entitled to inclusion of their securities in such
Registration Statement by reason of demand registration rights. No right to
registration of Registrable Securities under this Section 2(d) shall be
construed to limit any registration required under Section 2(a) hereof. If an
offering in connection with which an Investor is entitled to registration under
this Section 2(d) is an underwritten offering, then each Investor whose
Registrable Securities are included in such Registration Statement shall, unless
otherwise agreed by the Company, offer and sell such Registrable Securities in
an underwritten offering using the same underwriter or underwriters and, subject
to the provisions of this Agreement, on the same terms and conditions as other
shares of Common Stock included in such underwritten offering. Notwithstanding
anything to the contrary set forth herein, the registration rights of the
Investors pursuant to this Section 2(d) shall only be available in the event the
Company fails to timely file, obtain effectiveness or maintain effectiveness of
any Registration Statement to be filed pursuant to Section 2(a) in accordance
with the terms of this Agreement. Furthermore, in the event the Company files a
"shelf" Registration Statement contemplating future offerings thereunder for its
own account, the obligations of the Company and the rights of the Investors
under this Section 2(d) shall not commence until such time as the Company
determines to first commence an offering under such Registration Statement (i.e.
"take down" shares from such "shelf" Registration Statement).

                  e. ELIGIBILITY FOR FORM S-3. The Company represents and
warrants that it meets the registrant eligibility and transaction requirements
for the use of Form S-3 for registration of the sale by the Initial Investor and
any other Investors of the Registrable Securities and the Company shall file all
reports required to be filed by the Company with the SEC in a timely manner so
as to maintain such eligibility for the use of Form S-3.

         3. OBLIGATIONS OF THE COMPANY.

         In connection with the registration of the Registrable Securities, the
Company shall have the following obligations:

                  a. The Company shall prepare promptly, and file with the SEC
as soon as practicable after the Closing Date (but in no event later than the
Filing Date), a Registration Statement with respect to the number of Registrable
Securities provided in Section 2(a), and thereafter use its best efforts to
cause such Registration Statement relating to Registrable Securities to become
effective as soon as possible after such filing (but in no event later than the
Registration Deadline), and keep the Registration Statement effective pursuant
to Rule 415 at all times until such date as is the earlier of (i) the date on
which all of the Registrable Securities have been sold and (ii) the date on
which the Registrable Securities (in the opinion of counsel to the Initial
Investor) may be immediately sold to the public without registration or
restriction (including without limitation as to volume by each holder thereof)
under the 1933 Act (the "REGISTRATION PERIOD"), which Registration Statement
(including any amendments or supplements thereto and prospectuses contained
therein) shall not contain any untrue statement of a material fact or omit to
state a material fact required to be stated therein, or necessary to make the
statements therein not misleading.


                                     - 5 -
<PAGE>   6

                  b. The Company shall prepare and file with the SEC such
amendments (including post-effective amendments) and supplements to the
Registration Statements and the prospectus or prospectuses used in connection
with the Registration Statements as may be necessary to keep the Registration
Statements effective at all times during the Registration Period, and, during
such period, comply with the provisions of the 1933 Act with respect to the
disposition of all Registrable Securities of the Company covered by the
Registration Statements until such time as all of such Registrable Securities
have been disposed of in accordance with the intended methods of disposition by
the seller or sellers thereof as set forth in the Registration Statements. In
the event that on any Trading Day (as defined in the Debentures) (the
"REGISTRATION TRIGGER DATE") the number of shares available under all
Registration Statements filed pursuant to this Agreement is insufficient to
cover all of the Registrable Securities issued or issuable upon conversion of or
otherwise pursuant to the Debentures (based on the Conversion Price (as defined
in the Debentures) then in effect) and upon exercise of or otherwise pursuant to
the Warrants (based on the Exercise Price (as defined in the Warrants) then in
effect) in each case without giving effect to any limitations on the Investors'
ability to convert the Debentures or exercise the Warrants, the Company shall
amend the Registration Statement, or file a new Registration Statement (on the
short form available therefore, if applicable), or both, so as to cover 125% of
the Registrable Securities so issued or issuable (without giving effect to any
limitations on conversion or exercise contained in the Debentures or the
Warrants, as applicable), in each case, as soon as practicable, but in any event
within twenty (20) business days after the Registration Trigger Date. The
Company shall use its best efforts to cause such amendment and/or new
Registration Statement to become effective as soon as practicable following the
filing thereof but in any event within sixty (60) days of the Registration
Trigger Date. The provisions of Section 2(c) above shall be applicable with
respect to the Company's obligations under this Section 3(b).

                  c. The Company shall furnish to each Investor whose
Registrable Securities are included in a Registration Statement and its legal
counsel (i) promptly after the same is prepared and publicly distributed, filed
with the SEC, or received by the Company, one copy of each Registration
Statement and any amendment thereto, each preliminary prospectus and prospectus
and each amendment or supplement thereto, and, in the case of the Registration
Statement referred to in Section 2(a), each letter written by or on behalf of
the Company to the SEC or the staff of the SEC, and each item of correspondence
from the SEC or the staff of the SEC, in each case relating to such Registration
Statement (other than any portion of any thereof which contains information for
which the Company has sought confidential treatment), and (ii) such number of
copies of a prospectus, including a preliminary prospectus, and all amendments
and supplements thereto and such other documents as such Investor may reasonably
request in order to facilitate the disposition of the Registrable Securities
owned by such Investor. The Company will immediately notify each Investor by
facsimile of the effectiveness of each Registration Statement or any
post-effective amendment. The Company will promptly respond to any and all
comments received from the SEC, with a view towards causing each Registration
Statement or any amendment thereto to be declared effective by the SEC as soon
as practicable and shall promptly file an acceleration request as soon as
practicable following the resolution or clearance of all SEC comments or, if
applicable, following notification by the SEC that any such Registration
Statement or any amendment thereto will not be subject to review.


                                     - 6 -
<PAGE>   7

                  d. The Company shall use reasonable efforts to (i) register
and qualify the Registrable Securities covered by the Registration Statements
under such other securities or "blue sky" laws of such jurisdictions in the
United States as the Investors who hold a majority in interest of the
Registrable Securities being offered reasonably request, (ii) prepare and file
in those jurisdictions such amendments (including post-effective amendments) and
supplements to such registrations and qualifications as may be necessary to
maintain the effectiveness thereof during the Registration Period, (iii) take
such other actions as may be necessary to maintain such registrations and
qualifications in effect at all times during the Registration Period, and (iv)
take all other actions reasonably necessary or advisable to qualify the
Registrable Securities for sale in such jurisdictions; provided, however, that
the Company shall not be required in connection therewith or as a condition
thereto to (a) qualify to do business in any jurisdiction where it would not
otherwise be required to qualify but for this Section 3(d), (b) subject itself
to general taxation in any such jurisdiction, (c) file a general consent to
service of process in any such jurisdiction, (d) provide any undertakings that
cause the Company undue expense or burden, or (e) make any change in its charter
or bylaws, which in each case the Board of Directors of the Company determines
to be contrary to the best interests of the Company and its stockholders.

                  e. [Intentionally omitted].

                  f. As promptly as practicable after becoming aware of such
event, the Company shall notify each Investor of the happening of any event, of
which the Company has knowledge, as a result of which the prospectus included in
any Registration Statement, as then in effect, includes an untrue statement of a
material fact or omission to state a material fact required to be stated therein
or necessary to make the statements therein not misleading, and use its best
efforts promptly to prepare an amendment to any Registration Statement or
supplement to the prospectus contained therein necessary to correct such untrue
statement or omission, and deliver such number of copies of such supplement or
amendment to each Investor as such Investor may reasonably request; provided
that, for not more than thirty (30) consecutive trading days (or a total of not
more than sixty (60) trading days in any twelve (12) month period), the Company
may delay the disclosure of material non-public information concerning the
Company (as well as prospectus or Registration Statement updating) the
disclosure of which at the time is not, in the good faith opinion of the
Company, in the best interests of the Company (an "ALLOWED DELAY"); provided,
further, that the Company shall promptly (i) notify the Investors in writing of
the existence of (but in no event, without the prior written consent of an
Investor, shall the Company disclose to such Investor any of the facts or
circumstances regarding) material non-public information giving rise to an
Allowed Delay and (ii) advise the Investors in writing to cease all sales under
such Registration Statement until the end of the Allowed Delay. Upon expiration
of the Allowed Delay, the Company shall again be bound by the first sentence of
this Section 3(f) with respect to the information giving rise thereto.

                  g. The Company shall use its best efforts to prevent the
issuance of any stop order or other suspension of effectiveness of any
Registration Statement, and, if such an order is issued, to obtain the
withdrawal of such order at the earliest possible moment and to notify each
Investor who holds Registrable Securities being sold (or, in the event of an
underwritten offering, the managing underwriters) of the issuance of such order
and the resolution thereof.


                                     - 7 -
<PAGE>   8

                  h. The Company shall permit a single firm of counsel
designated by the Initial Investor to review such Registration Statement and all
amendments and supplements thereto (as well as all requests for acceleration or
effectiveness thereof) a reasonable period of time prior to their filing with
the SEC, and not file any document in a form to which such counsel reasonably
objects and will not request acceleration of such Registration Statement without
prior notice to such counsel. The sections of such Registration Statement
covering information with respect to the Investors, the Investors' beneficial
ownership of securities of the Company or the Investors' intended method of
disposition of Registrable Securities shall conform to the information provided
to the Company by the Investors.

                  i. The Company shall make generally available to its security
holders as soon as practicable, but not later than ninety (90) days after the
close of the period covered thereby, an earnings statement (in form complying
with the provisions of Rule 158 under the 1933 Act) covering a twelve-month
period beginning not later than the first day of the Company's fiscal quarter
next following the effective date of the Registration Statement.

                  j. [Intentionally omitted].

                  k. The Company shall make available for inspection at its
corporate offices during regular business hours by (i) any Investor, (ii) one
firm of attorneys and one firm of accountants or other agents retained by the
Initial Investor and (iii) one firm of attorneys and one firm of accountants or
other agents retained by all other Investors (collectively, the "INSPECTORS")
all pertinent financial and other records, and pertinent corporate documents and
properties of the Company (collectively, the "RECORDS"), as shall be reasonably
deemed necessary by each Inspector to enable each Inspector to exercise its due
diligence responsibility, and cause the Company's officers, directors and
employees to supply all information which any Inspector may reasonably request
for purposes of such due diligence; provided, however, that each Inspector shall
hold in confidence and shall not make any disclosure (except to an Investor) of
any Record or other information which the Company determines in good faith to be
confidential, and of which determination the Inspectors are so notified, unless
(a) the disclosure of such Records is necessary to avoid or correct a
misstatement or omission in any Registration Statement, (b) the release of such
Records is ordered pursuant to a subpoena or other order from a court or
government body of competent jurisdiction, or (c) the information in such
Records has been made generally available to the public other than by disclosure
in violation of this or any other agreement. The Company shall not be required
to disclose any confidential information in such Records to any Inspector until
and unless such Inspector shall have entered into confidentiality agreements (in
form and substance satisfactory to the Company) with the Company with respect
thereto, substantially in the form of this Section 3(k). Each Investor agrees
that it shall, upon learning that disclosure of such Records is sought in or by
a court or governmental body of competent jurisdiction or through other means,
give prompt notice to the Company and allow the Company, at its expense, to
undertake appropriate action to prevent disclosure of, or to obtain a protective
order for, the Records deemed confidential. Nothing herein (or in any other
confidentiality agreement between the Company and any Investor) shall be deemed
to limit the Investor's ability to sell Registrable Securities in a manner which
is otherwise consistent with applicable laws and regulations.


                                     - 8 -
<PAGE>   9

                  l. The Company shall hold in confidence and not make any
disclosure of information concerning an Investor provided to the Company unless
(i) disclosure of such information is necessary to comply with federal or state
securities laws, rules or regulations, or the rules and regulations of any
self-regulatory organization to which the Company or its securities are subject
(ii) the disclosure of such information is necessary to avoid or correct a
misstatement or omission in any Registration Statement, (iii) the release of
such information is ordered pursuant to a subpoena or other order from a court
or governmental body of competent jurisdiction, or (iv) such information has
been made generally available to the public other than by disclosure in
violation of this or any other agreement. The Company agrees that it shall, upon
learning that disclosure of such information concerning an Investor is sought in
or by a court or governmental body of competent jurisdiction or through other
means, give prompt notice to such Investor prior to making such disclosure, and
allow the Investor, at its expense, to undertake appropriate action to prevent
disclosure of, or to obtain a protective order for, such information.

                  m. The Company shall (i) cause all the Registrable Securities
covered by the Registration Statement to be listed on each national securities
exchange on which securities of the same class or series issued by the Company
are then listed, if any, if the listing of such Registrable Securities is then
permitted under the rules of such exchange, or (ii) to the extent the securities
of the same class or series are not then listed on a national securities
exchange, secure the designation and quotation, of all the Registrable
Securities covered by the Registration Statement on Nasdaq or, if not eligible
for Nasdaq on the Nasdaq SmallCap and, without limiting the generality of the
foregoing, to arrange for at least two market makers to register with the
National Association of Securities Dealers, Inc. ("NASD") as such with respect
to such Registrable Securities.

                  n. The Company shall provide a transfer agent and registrar,
which may be a single entity, for the Registrable Securities not later than the
effective date of the Registration Statement.

                  o. The Company shall cooperate with the holders of Registrable
Securities being offered to facilitate the timely preparation and delivery of
certificates (not bearing any restrictive legends) representing Registrable
Securities to be offered pursuant to a Registration Statement and enable such
certificates to be in such denominations or amounts, as the case may be, as such
holders may reasonably request and registered in such names as the Investors may
request, and, within three (3) business days after a Registration Statement
which includes Registrable Securities is ordered effective by the SEC, the
Company shall deliver, and shall cause legal counsel selected by the Company to
deliver, to the transfer agent for the Registrable Securities (with copies to
the Investors whose Registrable Securities are included in such Registration
Statement) an instruction in the form attached hereto as EXHIBIT 1 and an
opinion of such counsel in the form attached hereto as EXHIBIT 2.

                  p. At the request of the holders of a majority-in-interest of
the Registrable Securities, the Company shall prepare and file with the SEC such
amendments (including post-effective amendments) and supplements to a
Registration Statement and any prospectus used in connection with the
Registration Statement as may be necessary in order to change the plan of
distribution set forth in such Registration Statement. In addition, the Company
shall not offer any securities for its own account or the account of others in
any Registration Statement under Section


                                     - 9 -
<PAGE>   10

2(a) hereof or any amendment or supplement thereto under Section 3(b) hereof
without the consent of the majority-in-interest of the Registrable Securities.

                  q. From and after the date of this Agreement, the Company
shall not, and shall not agree to, allow the holders of any securities of the
Company to include any of their securities in any Registration Statement under
Section 2(a) hereof or any amendment or supplement thereto under Section 3(b)
hereof without the consent of the holders of a majority-in-interest of the
Registrable Securities.

                  r. The Company shall take all other reasonable actions
necessary to expedite and facilitate disposition by the Investors of Registrable
Securities pursuant to a Registration Statement.

                  s. The Company shall comply with all applicable laws related
to a Registration Statement and offering and sale of securities and all
applicable rules and regulations of governmental authorities in connection
therewith (including without limitation the 1933 Act and the Securities Exchange
Act of 1934, as amended (the "1934 ACT"), and the rules and regulations
promulgated by the SEC).

         4. OBLIGATIONS OF THE INVESTORS.

         In connection with the registration of the Registrable Securities, the
Investors shall have the following obligations:

                  a. It shall be a condition precedent to the obligations of the
Company to complete the registration pursuant to this Agreement with respect to
the Registrable Securities of a particular Investor that such Investor shall
furnish to the Company such information regarding itself, the Registrable
Securities held by it and the intended method of disposition of the Registrable
Securities held by it as shall be reasonably required to effect the registration
of such Registrable Securities and shall execute such documents in connection
with such registration as the Company may reasonably request. At least three (3)
business days prior to the first anticipated filing date of the Registration
Statement, the Company shall notify each Investor of the information the Company
requires from each such Investor and each Investor will provide such information
to the Company within 48 hours of receipt of such notice.

                  b. Each Investor, by such Investor's acceptance of the
Registrable Securities, agrees to cooperate with the Company as reasonably
requested by the Company in connection with the preparation and filing of the
Registration Statements hereunder, unless such Investor has notified the Company
in writing of such Investor's election to exclude all of such Investor's
Registrable Securities from the Registration Statements.

                  c. [Intentionally omitted].

                  d. Each Investor agrees that, upon receipt of any notice from
the Company of the happening of any event of the kind described in Section 3(f)
or 3(g), such Investor will


                                     - 10 -
<PAGE>   11

immediately discontinue disposition of Registrable Securities pursuant to the
Registration Statement covering such Registrable Securities until such
Investor's receipt of the copies of the supplemented or amended prospectus
contemplated by Section 3(f) or 3(g) and, if so directed by the Company, such
Investor shall deliver to the Company (at the expense of the Company) or destroy
(and deliver to the Company a certificate of destruction) all copies in such
Investor's possession, of the prospectus covering such Registrable Securities
current at the time of receipt of such notice.

                  e. Each Investor agrees to sell the Registrable Securities in
compliance with all applicable prospectus delivery requirements under the 1933
Act, pursuant to Rule 144 or pursuant to another available exemption under the
1933 Act.

         5. EXPENSES OF REGISTRATION.

         All reasonable expenses, other than underwriting discounts and
commissions, incurred in connection with registrations, filings or
qualifications pursuant to Sections 2 and 3, including, without limitation, all
registration, listing and qualification fees, printers and accounting fees, the
fees and disbursements of counsel for the Company, and, subject to Section
1.2(e) of the Securities Purchase Agreement, the reasonable fees and
disbursements of one counsel selected by the Initial Investor pursuant to
Sections 2(b) and 3(h) hereof shall be borne by the Company.

         6. INDEMNIFICATION.

         In the event any Registrable Securities are included in a Registration
Statement under this Agreement:

                  a. To the extent permitted by law, the Company will indemnify,
hold harmless and defend (i) each Investor who holds such Registrable
Securities, (ii) the directors, officers, partners, employees, agents and each
person who controls any Investor within the meaning of the 1933 Act or the 1934
Act, if any, (iii) any underwriter (as defined in the 1933 Act) for the
Investors, and (iv) the directors, officers, partners, employees and each person
who controls any such underwriter within the meaning of the 1933 Act or the 1934
Act, if any (each, an "INDEMNIFIED PERSON"), against any joint or several
losses, claims, damages, liabilities or expenses (collectively, together with
actions, proceedings or inquiries by any regulatory or self-regulatory
organization, whether commenced or threatened, in respect thereof, "CLAIMS") to
which any of them may become subject insofar as such Claims arise out of or are
based upon: (i) any untrue statement or alleged untrue statement of a material
fact in a Registration Statement or the omission or alleged omission to state
therein a material fact required to be stated or necessary to make the
statements therein not misleading; (ii) any untrue statement or alleged untrue
statement of a material fact contained in any preliminary prospectus if used
prior to the effective date of such Registration Statement, or contained in the
final prospectus (as amended or supplemented, if the Company files any amendment
thereof or supplement thereto with the SEC) or the omission or alleged omission
to state therein any material fact necessary to make the statements made
therein, in light of the circumstances under which the statements therein were
made, not misleading; or (iii) any violation or alleged violation by the Company
of the 1933 Act, the 1934 Act, any other law, including, without limitation, any
state securities law, or any rule or regulation thereunder relating to the offer
or sale of the Registrable


                                     - 11 -
<PAGE>   12

Securities (the matters in the foregoing clauses (i) through (iii) being,
collectively, "VIOLATIONS"). Subject to the restrictions set forth in Section
6(c) with respect to the number of legal counsel, the Company shall reimburse
the Indemnified Person, promptly as such expenses are incurred and are due and
payable, for any reasonable legal fees or other reasonable expenses incurred by
them in connection with investigating or defending any such Claim.
Notwithstanding anything to the contrary contained herein, the indemnification
agreement contained in this Section 6(a): (i) shall not apply to a Claim arising
out of or based upon a Violation which occurs in reliance upon and in conformity
with information furnished in writing to the Company by any Indemnified Person
or underwriter for such Indemnified Person expressly for use in connection with
the preparation of such Registration Statement or any such amendment thereof or
supplement thereto; (ii) shall not apply to amounts paid in settlement of any
Claim if such settlement is effected without the prior written consent of the
Company, which consent shall not be unreasonably withheld; (iii) with respect to
any preliminary prospectus, shall not inure to the benefit of any Indemnified
Person if the untrue statement or omission of material fact contained in the
preliminary prospectus was corrected on a timely basis in the prospectus, as
then amended or supplemented, such corrected prospectus was timely made
available by the Company pursuant to Section 3(c) hereof, and the Indemnified
Person was promptly advised in writing not to use the incorrect prospectus prior
to the use giving rise to a Violation and such Indemnified Person,
notwithstanding such advice, used it; and (iv) shall not apply to any Claim
solely arising from an Investor's failure to satisfy its prospectus delivery
obligations under the 1933 Act, if any, if such prospectus was timely made
available by the Company pursuant to Section 3(c) hereof. Such indemnity shall
remain in full force and effect regardless of any investigation made by or on
behalf of the Indemnified Person and shall survive the transfer of the
Registrable Securities by the Investors pursuant to Section 9.

                  b. In connection with any Registration Statement in which an
Investor is participating, each such Investor agrees severally and not jointly
to indemnify, hold harmless and defend, to the same extent and in the same
manner set forth in Section 6(a), the Company, each of its directors, each of
its officers who signs the Registration Statement, each person, if any, who
controls the Company within the meaning of the 1933 Act or the 1934 Act, any
underwriter and any other stockholder selling securities pursuant to the
Registration Statement or any of its directors or officers or any person who
controls such stockholder or underwriter within the meaning of the 1933 Act or
the 1934 Act (collectively and together with an Indemnified Person, an
"INDEMNIFIED PARTY"), against any Claim to which any of them may become subject,
under the 1933 Act, the 1934 Act or otherwise, insofar as such Claim (i) arises
out of or is based upon any Violation by such Investor, in each case to the
extent (and only to the extent) that such Violation occurs in reliance upon and
in conformity with written information furnished to the Company by such Investor
expressly for use in connection with such Registration Statement or (ii) arises
solely from an Investor's failure to satisfy its prospectus delivery obligations
under the 1933 Act, if any, if such prospectus was timely made available by the
Company pursuant to Section 3(c) hereof; and subject to Section 6(c) such
Investor will reimburse any legal or other expenses (promptly as such expenses
are incurred and are due and payable) reasonably incurred by them in connection
with investigating or defending any such Claim; provided, however, that the
indemnity agreement contained in this Section 6(b) shall not apply to amounts
paid in settlement of any Claim if such settlement is effected without the prior
written consent of such Investor, which consent shall not be unreasonably
withheld; provided, further, however, that the Investor shall be liable under
this Agreement (including this


                                     - 12 -
<PAGE>   13

Section 6(b) and Section 7) for only that amount as does not exceed the net
proceeds to such Investor as a result of the sale of Registrable Securities
pursuant to such Registration Statement. Such indemnity shall remain in full
force and effect regardless of any investigation made by or on behalf of such
Indemnified Party and shall survive the transfer of the Registrable Securities
by the Investors pursuant to Section 9. Notwithstanding anything to the contrary
contained herein, the indemnification agreement contained in this Section 6(b)
with respect to any preliminary prospectus shall not inure to the benefit of any
Indemnified Party if the untrue statement or omission of material fact contained
in the preliminary prospectus was corrected on a timely basis in the prospectus,
as then amended or supplemented.

                  c. Promptly after receipt by an Indemnified Person or
Indemnified Party under this Section 6 of notice of the commencement of any
action (including any governmental action), such Indemnified Person or
Indemnified Party shall, if a Claim in respect thereof is to be made against any
indemnifying party under this Section 6, deliver to the indemnifying party a
written notice of the commencement thereof, and the indemnifying party shall
have the right to participate in, and, to the extent the indemnifying party so
desires, jointly with any other indemnifying party similarly noticed, to assume
control of the defense thereof with counsel mutually satisfactory to the
indemnifying party and the Indemnified Person or the Indemnified Party, as the
case may be; provided, however, that an Indemnified Person or Indemnified Party
shall have the right to retain its own counsel with the fees and expenses to be
paid by the indemnifying party, if, in the reasonable opinion of counsel
retained by the indemnifying party, the representation by such counsel of the
Indemnified Person or Indemnified Party and the indemnifying party would be
inappropriate due to actual or potential differing interests between such
Indemnified Person or Indemnified Party and any other party represented by such
counsel in such proceeding. The indemnifying party shall pay for only one
separate legal counsel for the Indemnified Persons or the Indemnified Parties,
as applicable, and such legal counsel shall be selected by Investors holding a
majority-in-interest of the Registrable Securities included in the Registration
Statement to which the Claim relates (with the approval of the Initial
Investor), if the Investors are entitled to indemnification hereunder, or the
Company, if the Company is entitled to indemnification hereunder, as applicable.
The failure to deliver written notice to the indemnifying party within a
reasonable time of the commencement of any such action shall not relieve such
indemnifying party of any liability to the Indemnified Person or Indemnified
Party under this Section 6, except to the extent that the indemnifying party is
actually prejudiced in its ability to defend such action. The indemnification
required by this Section 6 shall be made by periodic payments of the amount
thereof during the course of the investigation or defense, as such expense,
loss, damage or liability is incurred and is due and payable.

         7. CONTRIBUTION.

         To the extent any indemnification by an indemnifying party is
prohibited or limited by law, the indemnifying party agrees to make the maximum
contribution with respect to any amounts for which it would otherwise be liable
under Section 6 to the fullest extent permitted by law; provided, however, that
(i) no contribution shall be made under circumstances where the maker would not
have been liable for indemnification under the fault standards set forth in
Section 6, (ii) no seller of Registrable Securities guilty of fraudulent
misrepresentation (within the meaning of Section 11(f) of the 1933 Act) shall be
entitled to contribution from any seller of Registrable Securities who was


                                     - 13 -
<PAGE>   14

not guilty of such fraudulent misrepresentation, and (iii) contribution
(together with any indemnification or other obligations under this Agreement) by
any seller of Registrable Securities shall be limited in amount to the net
amount of proceeds received by such seller from the sale of such Registrable
Securities.

         8. REPORTS UNDER THE 1934 ACT.

         With a view to making available to the Investors the benefits of Rule
144 promulgated under the 1933 Act or any other similar rule or regulation of
the SEC that may at any time permit the investors to sell securities of the
Company to the public without registration ("RULE 144"), the Company agrees to:

                  a. make and keep public information available, as those terms
are understood and defined in Rule 144;

                  b. file with the SEC in a timely manner all reports and other
documents required of the Company under the 1933 Act and the 1934 Act so long as
the Company remains subject to such requirements (it being understood that
nothing herein shall limit the Company's obligations under Section 4(c) of the
Securities Purchase Agreement) and the filing of such reports and other
documents is required for the applicable provisions of Rule 144; and

                  c. furnish to each Investor so long as such Investor owns
Registrable Securities, promptly upon request, (i) a written statement by the
Company that it has complied with the reporting requirements of Rule 144, the
1933 Act and the 1934 Act, (ii) a copy of the most recent annual or quarterly
report of the Company and such other reports and documents so filed by the
Company, and (iii) such other information as may be reasonably requested to
permit the Investors to sell such securities pursuant to Rule 144 without
registration.

         9. ASSIGNMENT OF REGISTRATION RIGHTS.

         The rights under this Agreement shall be automatically assignable by
the Investors to any transferee of all or any portion of Registrable Securities
if: (i) the Investor agrees in writing with the transferee or assignee to assign
such rights, and a copy of such agreement is furnished to the Company within a
reasonable time after such assignment, (ii) the Company is, within a reasonable
time after such transfer or assignment, furnished with written notice of (a) the
name and address of such transferee or assignee, and (b) the securities with
respect to which such registration rights are being transferred or assigned,
(iii) following such transfer or assignment, the further disposition of such
securities by the transferee or assignee is restricted under the 1933 Act and
applicable state securities laws, (iv) at or before the time the Company
receives the written notice contemplated by clause (ii) of this sentence, the
transferee or assignee agrees in writing with the Company to be bound by all of
the provisions contained herein, (v) such transfer shall have been made in
accordance with the applicable requirements of the Securities Purchase
Agreement, and (vi) such transferee shall be an "ACCREDITED INVESTOR" as that
term defined in Rule 501 of Regulation D promulgated under the 1933 Act. Any
transferee of Registrable Securities under this Section 9 shall have all the
rights and obligations of the Investors under this Agreement.


                                     - 14 -
<PAGE>   15

         10. AMENDMENT OF REGISTRATION RIGHTS.

         Provisions of this Agreement may be amended and the observance thereof
may be waived (either generally or in a particular instance and either
retroactively or prospectively), only with written consent of the Company, the
Initial Investor (to the extent such Initial Investor still owns Registrable
Securities) and Investors who hold a majority interest of the Registrable
Securities. Any amendment or waiver effected in accordance with this Section 10
shall be binding upon each Investor and the Company.

         11. MISCELLANEOUS.

                  a. A person or entity is deemed to be a holder of Registrable
Securities whenever such person or entity owns of record such Registrable
Securities. If the Company receives conflicting instructions, notices or
elections from two or more persons or entities with respect to the same
Registrable Securities, the Company shall act upon the basis of instructions,
notice or election received from the registered owner of such Registrable
Securities.

                  b. Any notices required or permitted to be given under the
terms hereof shall be sent by certified or registered mail (return receipt
requested) or delivered personally or by courier (including a recognized
overnight delivery service) or by facsimile and shall be effective five days
after being placed in the mail, if mailed by regular United States mail, or upon
receipt, if delivered personally or by courier (including a recognized overnight
delivery service) or by facsimile, in each case addressed to a party. The
addresses for such communications shall be:

                           If to the Company:

                           Geron Corporation
                           230 Constitution Drive
                           Menlo Park, California 94025
                           Attention: David Greenwood, Chief Financial Officer
                           Facsimile:  (650) 473-7701

                           With a copy to:

                           Latham & Watkins
                           135 Commonwealth Drive
                           Menlo Park, California 94025
                           Attention: Alan C. Mendelson, Esquire
                           Facsimile:  (650) 463-2600

If to an Investor: to the address set forth immediately below such Investor's
name on the signature pages to the Securities Purchase Agreement.


                                     - 15 -
<PAGE>   16

                  c. Failure of any party to exercise any right or remedy under
this Agreement or otherwise, or delay by a party in exercising such right or
remedy, shall not operate as a waiver thereof.

                  d. This Agreement shall be enforced, governed by and construed
in accordance with the laws of the State of Delaware applicable to agreements
made and to be performed in the State of Delaware (without regard to principles
of conflict of laws). Both parties irrevocably consent to the jurisdiction of
the United States federal courts and the state courts located in Delaware with
respect to any suit or proceeding based on or arising under this Agreement, the
agreements entered into in connection herewith or the transactions contemplated
hereby and thereby and irrevocably agree that all claims in respect of such suit
or proceeding may be determined in such courts. Both parties irrevocably waive
the defense of an inconvenient forum to the maintenance of such suit or
proceeding. Both parties further agree that service of process upon a party
mailed by first class mail shall be deemed in every respect effective service of
process upon the party in any such suit or proceeding. Nothing herein shall
affect either party's right to serve process in any other manner permitted by
law. Both parties agree that a final non-appealable judgment in any such suit or
proceeding shall be conclusive and may be enforced in other jurisdictions by
suit on such judgment or in any other lawful manner.

                  e. This Agreement and the Securities Purchase Agreement
(including all schedules and exhibits thereto) constitute the entire agreement
among the parties hereto with respect to the subject matter hereof and thereof.
There are no restrictions, promises, warranties or undertakings, other than
those set forth or referred to herein and therein. This Agreement and the
Securities Purchase Agreement supersede all prior agreements and understandings
among the parties hereto with respect to the subject matter hereof and thereof.

                  f. Subject to the requirements of Section 9 hereof, this
Agreement shall inure to the benefit of and be binding upon the successors and
assigns of each of the parties hereto.

                  g. The headings in this Agreement are for convenience of
reference only and shall not limit or otherwise affect the meaning hereof.

                  h. This Agreement may be executed in two or more counterparts,
each of which shall be deemed an original but all of which shall constitute one
and the same agreement. This Agreement, once executed by a party, may be
delivered to the other party hereto by facsimile transmission of a copy of this
Agreement bearing the signature of the party so delivering this Agreement.

                  i. Each party shall do and perform, or cause to be done and
performed, all such further acts and things, and shall execute and deliver all
such other agreements, certificates, instruments and documents, as the other
party may reasonably request in order to carry out the intent and accomplish the
purposes of this Agreement and the consummation of the transactions contemplated
hereby.


                                     - 16 -
<PAGE>   17

                  j. Except as otherwise provided herein, all consents and other
determinations to be made by the Investors pursuant to this Agreement shall be
made by Investors holding a majority of the Registrable Securities, determined
as if the all of the Debentures then outstanding have been converted into for
Registrable Securities.

                  k. The Company acknowledges that a breach by it of its
obligations hereunder will cause irreparable harm to each Investor by vitiating
the intent and purpose of the transactions contemplated hereby. Accordingly, the
Company acknowledges that the remedy at law for breach of its obligations
hereunder will be inadequate and agrees, in the event of a breach or threatened
breach by the Company of any of the provisions hereunder, that each Investor
shall be entitled, in addition to all other available remedies in law or in
equity, to an injunction or injunctions to prevent or cure breaches of the
provisions of this Agreement and to enforce specifically the terms and
provisions hereof, without the necessity of showing economic loss and without
any bond or other security being required.

                  l. The language used in this Agreement will be deemed to be
the language chosen by the parties to express their mutual intent, and no rules
of strict construction will be applied against any party.

                  m. In the event that any provision of this Agreement is
invalid or unenforceable under any applicable statute or rule of law, then such
provision shall be deemed inoperative to the extent that it may conflict
therewith and shall be deemed modified to conform with such statute or rule of
law. Any provision hereof which may prove invalid or unenforceable under any law
shall not affect the validity or enforceability of any other provision hereof.

                  n. The initial number of Registrable Securities included on
any Registration Statement and each increase to the number of Registrable
Securities included thereon shall be allocated pro rata among Investors based on
the number of Registrable Securities held by each Investor at the time of such
establishment or increase, as the case may be. In the event an Investor shall
sell or otherwise transfer any of such holder's Registrable Securities, each
transferee shall be allocated a pro rata portion of the number of Registrable
Securities included on a Registration Statement for such transferor. Any shares
of Common Stock included on a Registration Statement and which remain allocated
to any person or entity which does not hold any Registrable Securities shall be
allocated to the remaining Investors, pro rata based on the number of shares of
Registrable Securities then held by such investors. For the avoidance of doubt,
the number of Registrable Securities held by an Investor shall be determined as
if all Debentures and Warrants then outstanding and held by an Investor were
converted into or exercised for Registrable Securities.

                [REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]


                                     - 17 -
<PAGE>   18

                  IN WITNESS WHEREOF, the Company and the undersigned Initial
Investor have caused this Agreement to be duly executed as of the date first
above written.


                                       GERON CORPORATION


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


                                       RGC INTERNATIONAL INVESTORS, LDC

                                       By: Rose Glen Capital Management, L.P.,
                                           Investment Manager

                                       By: RGC General Partner Corp.,
                                           as General Partner



                                       By: /s/ WAYNE D. BLOCH
                                           -------------------------------------
                                           Wayne D. Bloch
                                           Managing Director


                                     - 18 -