RIBOGENE INC / CA/
S-8, 1998-09-18
COMMERCIAL PHYSICAL & BIOLOGICAL RESEARCH
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<PAGE>   1
   As filed with the Securities and Exchange Commission on September 18, 1998
                                                           Registration No. 333-

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549



                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

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

                                 RiboGene, Inc.
             (Exact name of registrant as specified in its charter)

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

       Delaware                                         94-3095154
(State of Incorporation)                    (I.R.S. Employer Identification No.)

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

                                 RiboGene, Inc.
                               26118 Research Road
                                Hayward, CA 94595
                    (Address of principal executive offices)

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

                           1997 Equity Incentive Plan
                       1997 Employee Stock Purchase Plan
                 1997 Non-Employee Directors' Stock Option Plan
                            (Full title of the plans)



                              Charles J. Casamento
                      President and Chief Executive Officer
                               26118 Research Road
                                Hayward, CA 94595
              -----------------------------------------------------
 (Name, address, including zip code, and telephone number, including area code,
                              of agent for service)


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

                                   Copies to:
                             Robert J. Brigham, Esq.
                               Cooley Godward LLP
                              FIVE PALO ALTO SQUARE
                               3000 EL CAMINO REAL
                            PALO ALTO, CA 94306-2155
                                 (650) 843-5000

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


<PAGE>   2
                         CALCULATION OF REGISTRATION FEE


<TABLE>
<CAPTION>
===========================================================================================================================
                                                      PROPOSED MAXIMUM          PROPOSED MAXIMUM
 TITLE OF SECURITIES TO        AMOUNT TO BE          OFFERING PRICE PER        AGGREGATE OFFERING             AMOUNT OF   
      BE REGISTERED             REGISTERED               SHARE (1)                 PRICE (1)              REGISTRATION FEE
===========================================================================================================================
<S>                            <C>                   <C>                       <C>                        <C>        
Stock  Options and Common
Stock (par value $.001)         1,480,000                  $3.03                   $4,484,400                  $1,323      
===========================================================================================================================
</TABLE>


(1)   Estimated solely for the purpose of calculating the amount of the
      registration fee pursuant to Rule 457(h) and 457(c). The price per share
      and aggregate offering price are based upon the average of the bid and ask
      prices of Registrant's Common Stock on September 11, 1998 as reported on
      the American Stock Exchange.





                                       2
<PAGE>   3
                 INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

      The following documents filed by RiboGene, Inc. (the "Company" or
"Registrant") with the Securities and Exchange Commission are incorporated by
reference into this Registration Statement:

      (a)   The Company's latest annual report on Form 10-K filed pursuant to
Sections 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended (the
"Exchange Act"), or either (1) the Company's latest prospectus filed pursuant to
Rule 424(b) under the Securities Act of 1933, as amended (the "Act"), that
contains audited financial statements for the Company's latest fiscal year for
which such statements have been filed, or (2) the Company's effective
registration statement on Form 10 or 20-F filed under the Exchange Act
containing audited financial statements for the Company's latest fiscal year.

      (b)   All other reports filed pursuant to Sections 13(a) or 15(d) of the
Exchange Act since the end of the fiscal year covered by the annual reports, the
prospectus or the registration statement referred to in (a) above. 

      (c)   The description of the Company's Common Stock which is contained in
a registration statement filed under the Exchange Act, including any amendment
or report filed for the purpose of updating such description.

      All reports and other documents subsequently filed by the Company pursuant
to Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act prior to the filing
of a post-effective amendment which indicates that all securities offered have
been sold or which deregisters all securities then remaining unsold, shall be
deemed to be incorporated by reference herein and to be a part of this
registration statement from the date of the filing of such reports and
documents.


                            DESCRIPTION OF SECURITIES

Not Applicable


                     INTERESTS OF NAMED EXPERTS AND COUNSEL

Not Applicable

                    INDEMNIFICATION OF DIRECTORS AND OFFICERS

The Registrant's Certificate of Incorporation and By-laws include provisions to
(i) eliminate the personal liability of its directors for monetary damages
resulting from breaches of their fiduciary duty to the extent permitted by
Section 102(b)(7) of the General Corporation Law of Delaware (the "Delaware
Law") and (ii) require the Registrant to indemnify its directors and officers to
the fullest extent permitted by Section 145 of the Delaware Law, including
circumstances in which indemnification is otherwise discretionary. Pursuant to
Section 145 of the Delaware Law, a corporation generally has the power to
indemnify its present and former directors, officers, employees and agents
against expenses incurred by them in connection with any suit to which they are,
or are threatened to be made, a party by reason of their serving in such
positions so long as they acted in good faith and in a manner they reasonably
believed to be in, or not opposed to, the best interests of a corporation, and,
with respect to any criminal action, they had no reasonably cause to believe
their conduct was unlawful. The Registrant believes that these provisions are
necessary to attract and retain qualified persons as directors and officers.
These provisions do not eliminate liability for breach of a director's duty of
loyalty to the Registrant or its stockholders, for acts or omissions not in good
faith or involving intentional misconduct or knowing violations of law, for any
transaction from which the director derived an improper personal benefit or for
any willful or negligent payment of any unlawful dividend or any unlawful stock
purchase agreement or redemption.

The Registrant has entered into agreements with its directors and executive
officers that which provide for indemnification under certain circumstances for
acts and omissions which may not be covered by any directors' and officers'
liability 




                                       1
<PAGE>   4
insurance. The Registrant has purchased an insurance policy covering the
officers and directors of the Registrant with respect to certain liabilities
arising under the Securities Act or otherwise.

                       EXEMPTION FROM REGISTRATION CLAIMED

Not Applicable


                                    EXHIBITS


EXHIBIT
NUMBER

5.1         Opinion of Cooley Godward LLP

23.1        Consent of Ernst & Young LLP

23.2        Consent of Cooley Godward is contained in Exhibit 5.1 to this
            Registration Statement.

24.1        Power of Attorney is contained on the signature pages

99.1        1997 Equity Incentive Plan

99.2        Form of Stock Option Agreement used in connection with the 1997
            Equity Incentive Plan.

99.3        1997 Employee Stock Purchase Plan

99.4        1997 Non-Employee Directors' Stock Option Plan

99.5        Form of Stock Option Agreement used in connection with the 1997
            Non-Employee Directors' Stock Option Plan.


                                  UNDERTAKINGS

1.    The undersigned registrant hereby undertakes:

      (a)   To file, during any period in which offers or sales are being made,
a post-effective amendment to this registration statement:

            (i)   To include any prospectus required by section 10(a)(3) of the
Securities Act;

            (ii)  To reflect in the prospectus any facts or events arising after
the effective date of the registration statement (or the most recent
post-effective amendment thereof) which, individually or in the aggregate,
represent a fundamental change in the information set forth in the registration
statement. Notwithstanding the foregoing, any increase or decrease in volume of
securities offered (if the total dollar value of securities offered would not
exceed that which was registered) and any deviation from the low or high end of
the estimated maximum offering range may be reflected in the form of prospectus
filed with the Commission pursuant to Rule 424(b) (Section 230.424(b) of this
chapter) if, in the aggregate, the 


                                       2
<PAGE>   5
changes in volume and price represent no more than a 20% change in the maximum
aggregate offering price set forth in the "Calculation of Registration Fee"
table in the effective registration statement. 

            (iii) To include any material information with respect to the plan
of distribution not previously disclosed in the registration statement or any
material change to such information in the registration statement; 

       Provided, however, that paragraphs (a)(i) and (a)(ii) do not apply if
the information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed by the issuer pursuant to
section 13 or section 15(d) of the Exchange Act that are incorporated by
reference herein.

      (b)   That, for the purpose of determining any liability under the
Securities Act, each such post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered herein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

      (c)   To remove from registration by means of a post-effective amendment
any of the securities being registered which remain unsold at the termination of
the offering. 

2.    The undersigned registrant hereby undertakes that, for purposes of
      determining any liability under the Securities Act, each filing of the
      registrant's annual report pursuant to Section 13(a) or Section 15(d) of
      the Exchange Act (and, where applicable, each filing of an employee
      benefit plan's annual report pursuant to section 15(d) of the Exchange
      Act) that is incorporated by reference in the Registration Statement shall
      be deemed to be a new registration statement relating to the securities
      offered herein, and the offering of such securities at that time shall be
      deemed to be the initial bona fide offering thereof.

3.    Insofar as indemnification for liabilities arising under the Securities
      Act may be permitted to directors, officers and controlling persons of the
      registrant pursuant to the foregoing provisions, or otherwise, the
      registrant has been advised that in the opinion of the Securities and
      Exchange Commission such indemnification is against public policy as
      expressed in the Securities Act and is, therefore, unenforceable. In the
      event that a claim for indemnification against such liabilities (other
      than the payment by the registrant of expenses incurred or paid by a
      director, officer or controlling person of the registrant in the
      successful defense of any action, suit or proceeding) is asserted by such
      director, officer or controlling person in connection with the securities
      being registered, the registrant will, unless in the opinion of its
      counsel the matter has been settled by controlling precedent, submit to a
      court of appropriate jurisdiction the question whether such
      indemnification by it is against public policy as expressed in the
      Securities Act and will be governed by the final adjudication of such
      issue.


                                       3
<PAGE>   6
                                   SIGNATURES

      Pursuant to the requirements of the Securities Act of 1933, as amended,
the Registrant certifies that it has reasonable grounds to believe that it meets
all of the requirements for filing on Form S-8 and has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Hayward State of California on September 17, 
1998.


                                 RIBOGENE, INC.


                             By      /s/ Timothy E. Morris
                                     -------------------------------------------

                             Title   Vice President, Finance and Administration
                                     and Chief Financial Officer



                                POWER OF ATTORNEY


      KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Charles J. Casamento and Timothy E.
Morris and each or any one of them, his true and lawful attorney-in-fact and
agent, with full power of substitution and resubstitution, for him and in his
name, place and stead, in any and all capacities, to sign any and all amendments
(including post-effective amendments) to this Registration Statement, and to
file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, granting unto said
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite and necessary to be done in
connection therewith, as fully to all intents and purposes as he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents, or any of them, or their or his substitutes or substitute, may
lawfully do or cause to be done by virtue hereof.


                                       4
<PAGE>   7
      Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the dates indicated.


<TABLE>
<CAPTION>
SIGNATURE                                             TITLE                                        DATE
<S>                                                   <C>                                          <C>


/s/ Charles J. Casamento                              President, Chief Executive Officer           September 17, 1998
- --------------------------------------------          And Director
         (Charles J. Casamento)                       



/s/ Timothy E. Morris                                 Vice President, Finance and                  September 17, 1998
- --------------------------------------------          Administration, Chief Financial Officer
         (Timothy E. Morris)                          and Assistant Secretary (Principal
                                                      Financial and Accounting Officer)       
                                                      



/s/ Digby W. Barrios                                  Director                                     September 17, 1998
- --------------------------------------------
          (Digby W. Barrios)



/s/ Frank J. Sasinowski                               Director                                     September 17, 1998
- --------------------------------------------
         (Frank J. Sasinowski)



/s/ Jon S. Saxe                                       Director                                     September 17, 1998
- --------------------------------------------
            (Jon S. Saxe)



/s/ Roger G. Stoll                                    Director                                     September 17, 1998
- --------------------------------------------
         (Roger G. Stoll, Ph.D.)
</TABLE>


                                       5
<PAGE>   8
                                  EXHIBIT INDEX


EXHIBIT
NUMBER                        DESCRIPTION

5.1         Opinion of Cooley Godward LLP

23.1        Consent of Ernst & Young LLP

23.2        Consent of Cooley Godward is contained in Exhibit 5.1 to this
            Registration Statement.

24.1        Power of Attorney is contained on the signature pages

99.1        1997 Equity Incentive Plan

99.2        Form of Stock Option Agreement used in connection with the 1997
            Equity Incentive Plan.

99.3        1997 Employee Stock Purchase Plan

99.4        1997 Non-Employee Directors' Stock Option Plan

99.5        Form of Stock Option Agreement used in connection with the 1997
            Non-Employee Directors' Stock Option Plan.


                                       6

<PAGE>   1
                                                                    Exhibit 5.1

September 18, 1998


RiboGene, Inc.
26118 Research Road
Hayward, CA  94595



Ladies and Gentlemen:

You have requested our opinion with respect to certain matters in connection
with the filing by RiboGene, Inc. (the "Company") of a Registration Statement on
Form S-8 (the "Registration Statement") with the Securities and Exchange
Commission covering the offering of up to 1,480,000 shares of the Company's
Common Stock, $.001 par value, (the "Shares") pursuant to its 1997 Equity
Incentive Plan, 1997 Employee Stock Purchase Plan and 1997 Non-Employee
Directors' Stock Option Plan (together, the "Plans").

In connection with this opinion, we have examined the Registration Statement and
related Prospectus, your Certificate of Incorporation and By-laws, as amended,
and such other documents, records, certificates, memoranda and other instruments
as we deem necessary as a basis for this opinion. We have assumed the
genuineness and authenticity of all documents submitted to us as originals, the
conformity to originals of all documents submitted to us as copies thereof, and
the due execution and delivery of all documents where due execution and delivery
are a prerequisite to the effectiveness thereof.

On the basis of the foregoing, and in reliance thereon, we are of the opinion
that the Shares, when sold and issued in accordance with the Plans, the
Registration Statement and related Prospectus, will be validly issued, fully
paid, and nonassessable (except as to shares issued pursuant to certain deferred
payment arrangements, which will be fully paid and nonassessable when such
deferred payments are made in full).

We consent to the filing of this opinion as an exhibit to the Registration
Statement.

Very truly yours,

COOLEY GODWARD LLP



By: /s/ Robert J. Brigham
    ------------------------------------
        Robert J. Brigham


                                       7

<PAGE>   1
                                                                    EXHIBIT 23.1


               CONSENT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS

We consent to the incorporation by reference in the Registration Statement on
Form S-8 pertaining to the 1997 Equity Incentive Plan, Employee Stock Purchase
Plan, and 1997 Non-Employee Directors' Stock Option Plan of RiboGene, Inc. of
our report dated January 23, 1998 (except Note 9, as to which the date is May
19, 1998), with respect to the financial statements of RiboGene, Inc. for the
year ended December 31, 1997 included in the Registration Statement on Form S-1
(No. 333-38781) and related Prospectus dated May 28, 1998.


                                       Ernst & Young LLP


Palo Alto, California
September 18, 1998

<PAGE>   1
                                 RIBOGENE, INC.

                           1997 EQUITY INCENTIVE PLAN

               ADOPTED BY THE BOARD OF DIRECTORS ON MARCH 8, 1998
                       APPROVED BY STOCKHOLDERS APRIL 1998


1.       PURPOSES.

         (a) The purpose of the 1997 Equity Incentive Plan (the "Plan") is to
provide a means by which selected Employees and Directors of and Consultants to
the Company and its Affiliates may be given an opportunity to benefit from
increases in value of the common stock of the Company ("Common Stock") through
the granting of (i) Incentive Stock Options, (ii) Nonstatutory Stock Options,
(iii) stock bonuses and (iv) rights to purchase restricted stock, all as defined
below.

         (b) The Company, by means of the Plan, seeks to retain the services of
persons who are now Employees, Directors or Consultants, to secure and retain
the services of new Employees, Directors and Consultants, and to provide
incentives for such persons to exert maximum efforts for the success of the
Company and its Affiliates.

         (c) The Company intends that the Stock Awards issued under the Plan
shall, in the discretion of the Board or any Committee to which responsibility
for administration of the Plan has been delegated pursuant to subsection 3(c),
be either (i) Options granted pursuant to Section 6 hereof, including Incentive
Stock Options and Nonstatutory Stock Options, or (ii) stock bonuses or rights to
purchase restricted stock granted pursuant to Section 7 hereof. All Options
shall be separately designated Incentive Stock Options or Nonstatutory Stock
Options at the time of grant, and a separate certificate or certificates will be
issued for shares purchased on exercise of each type of Option.

2.       DEFINITIONS.

         (a) "AFFILIATE" means any parent corporation or subsidiary corporation,
whether now or hereafter existing, as those terms are defined in Sections 424(e)
and (f) respectively, of the Code.

         (b) "BOARD" means the Board of Directors of the Company.

         (c) "CAUSE" means willful conduct that is materially injurious to the
Company (or any Affiliate) or any successor thereto, whether financial or
otherwise.

         (d) "CODE" means the Internal Revenue Code of 1986, as amended.

         (e) "COMMITTEE" means a Committee appointed by the Board in accordance
with subsection 3(c) of the Plan.

         (f) "COMPANY" means RiboGene, Inc., a Delaware corporation.


<PAGE>   2
         (g) "CONSULTANT" means any person, including an advisor, engaged by the
Company or an Affiliate to render consulting services and who is compensated for
such services, provided that the term "Consultant" shall not include Directors
who are paid only a director's fee by the Company or who are not compensated by
the Company for their services as Directors.

         (h) "CONTINUOUS SERVICE" means a person's continuous service for the
Company or an Affiliate of the Company, whether as an Employee, Director or
Consultant, is not interrupted or terminated. The Board, in its sole discretion,
may determine whether Continuous Service shall be considered interrupted in the
case of: (i) any leave of absence approved by the Board, including sick leave,
military leave, or any other personal leave; or (ii) transfers between locations
of the Company or between the Company, its Affiliates or their successors.

         (i) "DIRECTOR" means a member of the Board.

         (j) "EMPLOYEE" means any person, including Officers and Directors,
employed by the Company or any Affiliate of the Company. Neither service as a
Director nor payment of a director's fee by the Company shall be sufficient to
constitute "employment" by the Company.

         (k) "EXCHANGE ACT" means the Securities Exchange Act of 1934, as
amended.

         (l) "FAIR MARKET VALUE" means, as of any date, the value of the Common
Stock of the Company determined as follows:

                  (1) If the Common Stock is listed on any established stock
exchange, or traded on the Nasdaq National Market or The Nasdaq SmallCap Market,
the Fair Market Value of a share of Common Stock shall be the closing sales
price for such stock (or the closing bid, if no sales were reported) as quoted
on such exchange or market (or the exchange or market with the greatest volume
of trading in Common Stock) on the last market trading day prior to
determination, as reported in The Wall Street Journal or such other source as
the Board deems reliable;

                  (2) In the absence of such markets for the Common Stock, the
Fair Market Value shall be determined in good faith by the Board.

         (m) "INCENTIVE STOCK OPTION" means an Option intended to qualify as an
incentive stock option within the meaning of Section 422 of the Code and the
regulations promulgated thereunder.

         (n) "LISTING DATE" means the first date upon which any security of the
Company is listed (or approved for listing) upon notice of issuance on any
securities exchange, or designated (or approved for designation) upon notice of
issuance as a national market security on an interdealer quotation system if
such securities exchange or interdealer quotation system has been certified in
accordance with the provisions of Section 25100(o) of the California Corporate
Securities Law of 1968.

         (o) "NON-EMPLOYEE DIRECTOR" means a Director who either (i) is not a
current Employee or Officer of the Company or its parent or subsidiary, does not
receive compensation 


                                       2
<PAGE>   3
(directly or indirectly) from the Company or its parent or subsidiary for
services rendered as a consultant or in any capacity other than as a Director
(except for an amount as to which disclosure would not be required under Item
404(a) of Regulation S-K promulgated pursuant to the Securities Act of 1933
("Regulation S-K"), does not possess an interest in any other transaction as to
which disclosure would be required under Item 404(a) of Regulation S-K, and is
not engaged in a business relationship as to which disclosure would be required
under Item 404(b) of Regulation S-K; or (ii) is otherwise considered a
"non-employee director" for purposes of Rule 16b-3.

         (p) "NONSTATUTORY STOCK OPTION" means an Option not intended to qualify
as an Incentive Stock Option.

         (q) "OFFICER" means a person who is an officer of the Company within
the meaning of Section 16 of the Exchange Act and the rules and regulations
promulgated thereunder.

         (r) "OPTION" means a stock option granted pursuant to the Plan.

         (s) "OPTION AGREEMENT" means a written agreement between the Company
and an Optionee evidencing the terms and conditions of an individual Option
grant. Each Option Agreement shall be subject to the terms and conditions of the
Plan.

         (t) "OPTIONEE" means a person to whom an Option is granted pursuant to
the Plan.

         (u) "OUTSIDE DIRECTOR" means a Director who either (i) is not a current
employee of the Company or an "affiliated corporation" (within the meaning of
Treasury regulations promulgated under Section 162(m) of the Code), is not a
former employee of the Company or an "affiliated corporation" receiving
compensation for prior services (other than benefits under a tax qualified
pension plan), was not an officer of the Company or an "affiliated corporation"
at any time, and is not currently receiving direct or indirect remuneration from
the Company or an "affiliated corporation" for services in any capacity other
than as a Director, or (ii) is otherwise considered an "outside director" for
purposes of Section 162(m) of the Code.

         (v) "PLAN" means this 1997 Equity Incentive Plan.

         (w) "RULE 16B-3" means Rule 16b-3 of the Exchange Act or any successor
to Rule 16b-3, as in effect when discretion is being exercised with respect to
the Plan.

         (x) "STOCK AWARD" means any right granted under the Plan, including any
Option, any stock bonus, and any right to purchase restricted stock.

         (y) "STOCK AWARD AGREEMENT" means a written agreement between the
Company and a holder of a Stock Award evidencing the terms and conditions of an
individual Stock Award grant. Each Stock Award Agreement shall be subject to the
terms and conditions of the Plan.

3.       ADMINISTRATION.

         (a) The Plan shall be administered by the Board unless and until the
Board delegates administration to a Committee, as provided in subsection 3(c).


                                       3


<PAGE>   4
         (b) The Board shall have the power, subject to, and within the
limitations of, the express provisions of the Plan:

                  (1) To determine from time to time which of the persons
eligible under the Plan shall be granted Stock Awards; when and how each Stock
Award shall be granted; whether a Stock Award will be an Incentive Stock Option,
a Nonstatutory Stock Option, a stock bonus, a right to purchase restricted
stock, or a combination of the foregoing; the provisions of each Stock Award
granted (which need not be identical), including the time or times when a person
shall be permitted to receive stock pursuant to a Stock Award; and the number of
shares with respect to which a Stock Award shall be granted to each such person.

                  (2) To construe and interpret the Plan and Stock Awards
granted under it, and to establish, amend and revoke rules and regulations for
its administration. The Board, in the exercise of this power, may correct any
defect, omission or inconsistency in the Plan or in any Stock Award Agreement,
in a manner and to the extent it shall deem necessary or expedient to make the
Plan fully effective.

                  (3) To amend the Plan or a Stock Award as provided in Section
13.

                  (4) Generally, to exercise such powers and to perform such
acts as the Board deems necessary or expedient to promote the best interests of
the Company which are not in conflict with the provisions of the Plan.

         (c) The Board may delegate administration of the Plan to a committee or
committees ("Committee") of two or more members of the Board. In the discretion
of the Board, a Committee may consist solely of two (2) or more Outside
Directors, in accordance with Code Section 162(m), or solely of two (2) or more
Non-Employee Directors, in accordance with Rule 16b-3. If administration is
delegated to a Committee, the Committee shall have, in connection with the
administration of the Plan, the powers theretofore possessed by the Board (and
references in this Plan to the Board shall thereafter be to the Committee),
subject, however, to such resolutions, not inconsistent with the provisions of
the Plan, as may be adopted from time to time by the Board. The Board may
abolish the Committee at any time and revest in the Board the administration of
the Plan.

4.       SHARES SUBJECT TO THE PLAN.

         (a) Subject to the provisions of Section 11 relating to adjustments
upon changes in stock, the stock that may be issued pursuant to Stock Awards
shall not exceed in the aggregate eight hundred thousand shares (800,000) shares
of Common Stock. If any Stock Award shall for any reason expire or otherwise
terminate, in whole or in part, without having been exercised in full, the stock
not acquired under such Stock Award shall revert to and again become available
for issuance under the Plan.

         (b) The stock subject to the Plan may be unissued shares or reacquired
shares, bought on the market or otherwise.


                                       4


<PAGE>   5
5.       ELIGIBILITY.

         (a) Incentive Stock Options may be granted only to Employees. Stock
Awards other than Incentive Stock Options may be granted only to Employees,
Directors or Consultants.

         (b) No person shall be eligible for the grant of an Incentive Stock
Option if, at the time of grant, such person owns (or is deemed to own pursuant
to Section 424(d) of the Code) stock possessing more than ten percent (10%) of
the total combined voting power of all classes of stock of the Company or of any
of its Affiliates unless the exercise price of such Option is at least one
hundred ten percent (110%) of the Fair Market Value of such stock at the date of
grant and the Option is not exercisable after the expiration of five (5) years
from the date of grant.

         (c) Subject to the provisions of Section 11 relating to adjustments
upon changes in stock, no person shall be eligible to be granted Stock Awards
covering more than three hundred thousand (300,000) shares of Common Stock in
any calendar year.

6.       OPTION PROVISIONS.

         Each Option shall be in such form and shall contain such terms and
conditions as the Board shall deem appropriate. The provisions of separate
Options need not be identical, but each Option shall include (through
incorporation of provisions hereof by reference in the Option Agreement or
otherwise) the substance of each of the following provisions:

         (a) TERM. No Option shall be exercisable after the expiration of ten
(10) years from the date it was granted.

         (b) PRICE. The exercise price of each Incentive Stock Option shall be
not less than one hundred percent (100%) of the Fair Market Value of the stock
subject to the Option on the date the Option is granted, and the exercise price
of each Nonstatutory Stock Option shall be not less than eighty-five percent
(85%) of the Fair Market Value of the stock subject to the Option on the date
the Option is granted. Notwithstanding the foregoing, an Option may be granted
with an exercise price lower than that set forth in the preceding sentence if
such Option is granted pursuant to an assumption or substitution for another
option in a manner satisfying the provisions of Section 424(a) of the Code.

         (c) CONSIDERATION. The purchase price of stock acquired pursuant to an
Option shall be paid, to the extent permitted by applicable statutes and
regulations, either (i) in cash at the time the Option is exercised, or (ii) at
the discretion of the Board or Committee, at the time of the grant of the
Option, (A) by delivery to the Company of other Common Stock of the Company, (B)
according to a deferred payment or other arrangement (which may include, without
limiting the generality of the foregoing, the use of other Common Stock of the
Company) with the person to whom the Option is granted or to whom the Option is
transferred pursuant to subsection 6(d), or (C) in any other form of legal
consideration that may be acceptable to the Board. In the case of any deferred
payment arrangement, interest shall be payable at least annually and shall be
charged at the minimum rate of interest necessary to avoid the treatment as
interest, under any applicable provisions of the Code, of any amounts other than
amounts stated to be interest under 


                                       5


<PAGE>   6
the deferred payment arrangement. In addition, the "par value" of stock acquired
under an Option may not be paid pursuant to a deferred compensation arrangement.

         (d) TRANSFERABILITY. An Incentive Stock Option shall not be
transferable except by will or by the laws of descent and distribution, and
shall be exercisable during the lifetime of the person to whom the Incentive
Stock Option is granted only by such person. A Nonstatutory Stock Option may be
transferred to the extent provided in the Option Agreement; provided that if the
Option Agreement does not expressly permit transfer, then such Nonstatutory
Stock Option shall not be transferable except by will, by the laws of descent
and distribution or pursuant to a domestic relations order satisfying the
requirements of Rule 16b-3, and shall be exercisable during the lifetime of the
person to whom the Option is granted only by such person or any transferee
pursuant to a domestic relations order. Notwithstanding the foregoing, the
person to whom the Option is granted may, by delivering written notice to the
Company, in a form satisfactory to the Company, designate a third party who, in
the event of the death of the Optionee, shall thereafter be entitled to exercise
the Option.

         (e) VESTING. The total number of shares of stock subject to an Option
may, but need not, be allotted in periodic installments (which may, but need
not, be equal). The Option Agreement may provide that from time to time during
each of such installment periods, the Option may become exercisable ("vest")
with respect to some or all of the shares allotted to that period, and may be
exercised with respect to some or all of the shares allotted to such period
and/or any prior period as to which the Option became vested but was not fully
exercised. The Option may be subject to such other terms and conditions on the
time or times when it may be exercised (which may be based on performance or
other criteria) as the Board may deem appropriate. The provisions of this
subsection 6(e) are subject to any Option provisions governing the minimum
number of shares as to which an Option may be exercised.

         (f) TERMINATION OF CONTINUOUS SERVICE. In the event an Optionee's
Continuous Service terminates (other than upon the Optionee's death or
disability) and subject to the provisions of Section 11, the Optionee may
exercise his or her Option within such period of time designated by the Board,
which shall in no event be later than the expiration of the term of the Option
as set forth in the Option Agreement (the "Post-Termination Exercise Period")
and only to the extent that the Optionee was entitled to exercise the Option on
the date Optionee's Continuous Service terminates. The Board may at any time,
with the consent of the Optionee, extend the Post-Termination Exercise Period
and provide for continued vesting; provided however, that any extension of such
period by the Board in excess of three (3) months from the date of termination
shall cause an Incentive Stock Option so extended to become a Nonstatutory Stock
Option, effective as of the date of Board action. If, at the date of
termination, the Optionee is not entitled to exercise his or her entire Option,
the shares covered by the unexercisable portion of the Option shall revert to
the Plan. If, after termination, the Optionee does not exercise his or her
Option within the time specified in the Option Agreement or as otherwise
determined above, the Option shall terminate, and the shares covered by such
Option shall revert to the Plan. Notwithstanding the foregoing, the Board shall
have the power to permit an Option to continue to vest during the
Post-Termination Exercise Period.

         (g) DISABILITY OF OPTIONEE. In the event an Optionee's Continuous
Service terminates as a result of the Optionee's disability, the Optionee may
exercise his or her Option 


                                       6


<PAGE>   7
(to the extent that the Optionee was entitled to exercise it at the date of
termination), but only within such period of time ending on the earlier of (i)
the date twelve (12) months following such termination (or such longer or
shorter period specified in the Option Agreement), or (ii) the expiration of the
term of the Option as set forth in the Option Agreement. If, at the date of
termination, the Optionee is not entitled to exercise his or her entire Option,
the shares covered by the unexercisable portion of the Option shall revert to
and again become available for issuance under the Plan. If, after termination,
the Optionee does not exercise his or her Option within the time specified
herein, the Option shall terminate, and the shares covered by such Option shall
revert to and again become available for issuance under the Plan.

         (h) DEATH OF OPTIONEE. In the event of the death of an Optionee during,
or within a three (3)-month period after the termination of, the Optionee's
Continuous Service, the Option may be exercised to the extent vested by the
Optionee's estate, by a person who acquired the right to exercise the Option by
bequest or inheritance or by a person designated to exercise the option upon the
Optionee's death pursuant to subsection 6(d), but only within the period ending
on the earlier of (i) the date eighteen (18) months following the date of death
(or such longer or shorter period specified in the Option Agreement), or (ii)
the expiration of the term of such Option as set forth in the Option Agreement.
If, at the time of death, the Optionee was not entitled to exercise his or her
entire Option, the shares covered by the unexercisable portion of the Option
shall revert to and again become available for issuance under the Plan. If,
after death, the Option is not exercised within the time specified herein, the
Option shall terminate, and the shares covered by such Option shall revert to
and again become available for issuance under the Plan.

         (i) EARLY EXERCISE. The Option may, but need not, include a provision
whereby the Optionee may elect at any time while an Employee, Director or
Consultant to exercise the Option as to any part or all of the shares subject to
the Option prior to the full vesting of the Option. Any unvested shares so
purchased may be subject to a repurchase right in favor of the Company or to any
other restriction the Board determines to be appropriate.

7.       TERMS OF STOCK BONUSES AND PURCHASES OF RESTRICTED STOCK.

         Each stock bonus or restricted stock purchase agreement shall be in
such form and shall contain such terms and conditions as the Board or Committee
shall deem appropriate. The terms and conditions of stock bonus or restricted
stock purchase agreements may change from time to time, and the terms and
conditions of separate agreements need not be identical, but each stock bonus or
restricted stock purchase agreement shall include (through incorporation of
provisions hereof by reference in the agreement or otherwise) the substance of
each of the following provisions as appropriate:

         (a) PURCHASE PRICE. The purchase price under each restricted stock
purchase agreement shall be such amount as the Board or Committee shall
determine and designate in such agreement, but in no event shall the purchase
price be less than eighty-five percent (85%) of the stock's Fair Market Value on
the date such award is made. Notwithstanding the foregoing, the Board or
Committee may determine that eligible participants in the Plan may be awarded
stock pursuant to a stock bonus agreement in consideration for past services
actually rendered to the Company for its benefit.


                                       7


<PAGE>   8
         (b) TRANSFERABILITY. No rights under a stock bonus or restricted stock
purchase agreement shall be transferable except by will or the laws of descent
and distribution or, if the agreement so provides, pursuant to a domestic
relations order satisfying the requirements of Rule 16b-3, so long as stock
awarded under such agreement remains subject to any restrictions pursuant to the
agreement.

         (c) CONSIDERATION. The purchase price of stock acquired pursuant to a
stock purchase agreement shall be paid either: (i) in cash at the time of
purchase; (ii) at the discretion of the Board or Committee, according to a
deferred payment or other arrangement with the person to whom the stock is sold;
or (iii) in any other form of legal consideration that may be acceptable to the
Board or Committee in its discretion. Notwithstanding the foregoing, the Board
or Committee to which administration of the Plan has been delegated may award
stock pursuant to a stock bonus agreement in consideration for past services
actually rendered to the Company or for its benefit.

         (d) VESTING. Shares of stock sold or awarded under the Plan may, but
need not, be subject to a repurchase option in favor of the Company in
accordance with a vesting schedule to be determined by the Board or Committee.

         (e) TERMINATION OF CONTINUOUS SERVICE. In the event a Participant's
Continuous Service terminates, the Company may repurchase or otherwise reacquire
any or all of the shares of stock held by that person which have not vested as
of the date of termination under the terms of the stock bonus or restricted
stock purchase agreement between the Company and such person, subject to the
provisions of Section 11.

8.       COVENANTS OF THE COMPANY.

         (a) During the terms of the Stock Awards, the Company shall keep
available at all times the number of shares of stock required to satisfy such
Stock Awards.

         (b) The Company shall seek to obtain from each regulatory commission or
agency having jurisdiction over the Plan such authority as may be required to
issue and sell shares under Stock Awards; provided, however, that this
undertaking shall not require the Company to register under the Securities Act
of 1933, as amended (the "Securities Act") either the Plan, any Stock Award or
any stock issued or issuable pursuant to any such Stock Award. If, after
reasonable efforts, the Company is unable to obtain from any such regulatory
commission or agency the authority which counsel for the Company deems necessary
for the lawful issuance and sale of stock under the Plan, the Company shall be
relieved from any liability for failure to issue and sell stock upon exercise of
such Stock Awards unless and until such authority is obtained.

9.       USE OF PROCEEDS FROM STOCK.

         Proceeds from the sale of stock pursuant to Stock Awards shall
constitute general funds of the Company.


                                       8


<PAGE>   9
10.      MISCELLANEOUS.

         (a) The Board shall have the power to accelerate the time at which a
Stock Award may first be exercised or the time during which a Stock Award or any
part thereof will vest, notwithstanding the provisions in the Stock Award
stating the time at which it may first be exercised or the time during which it
will vest.

         (b) Neither an Employee, Director nor a Consultant nor any person to
whom a Stock Award is transferred in accordance with the Plan shall be deemed to
be the holder of, or to have any of the rights of a holder with respect to, any
shares subject to such Stock Award unless and until such person has satisfied
all requirements for exercise of the Stock Award pursuant to its terms.

         (c) Nothing in the Plan or any instrument executed or Stock Award
granted pursuant thereto shall confer upon any Employee, Consultant or other
holder of Stock Awards any right to continue in the employ of the Company or any
its Affiliates, or to continue serving as a Consultant and Director, or shall
affect the right of the Company or any of its Affiliates to terminate the
employment of any Employee with or without notice and with or without cause, the
right to terminate the relationship of any Consultant pursuant to the terms of
such Consultant's agreement with the Company or any of its Affiliates or service
as a Director pursuant to the Company's By-Laws.

         (d) To the extent that the aggregate Fair Market Value (determined at
the time of grant) of stock with respect to which Incentive Stock Options are
exercisable for the first time by any Optionee during any calendar year under
all plans of the Company and its Affiliates exceeds one hundred thousand dollars
($100,000), the Options or portions thereof which exceed such limit (according
to the order in which they were granted) shall be treated as Nonstatutory Stock
Options.

         (e) The Company may require any person to whom a Stock Award is
granted, or any person to whom a Stock Award is transferred in accordance with
the Plan, as a condition of exercising or acquiring stock under any Stock Award,
(1) to give written assurances satisfactory to the Company as to such person's
knowledge and experience in financial and business matters and/or to employ a
purchaser representative reasonably satisfactory to the Company who is
knowledgeable and experienced in financial and business matters, and that he or
she is capable of evaluating, alone or together with the purchaser
representative, the merits and risks of exercising the Stock Award; and (2) to
give written assurances satisfactory to the Company stating that such person is
acquiring the stock subject to the Stock Award for such person's own account and
not with any present intention of selling or otherwise distributing the stock.
The foregoing requirements, and any assurances given pursuant to such
requirements, shall be inoperative if (i) the issuance of the shares upon the
exercise or acquisition of stock under the Stock Award has been registered under
a then currently effective registration statement under the Securities Act, or
(ii) as to any particular requirement, a determination is made by counsel for
the Company that such requirement need not be met in the circumstances under the
then applicable securities laws. The Company may, upon advice of counsel to the
Company, place legends on stock certificates issued under the Plan as such
counsel deems necessary or appropriate in order to comply with 


                                       9


<PAGE>   10
applicable securities laws, including, but not limited to, legends restricting
the transfer of the stock.

         (f) To the extent provided by the terms of a Stock Award Agreement, the
person to whom a Stock Award is granted may satisfy any federal, state or local
tax withholding obligation relating to the exercise or acquisition of stock
under a Stock Award by any of the following means or by a combination of such
means: (1) tendering a cash payment; (2) authorizing the Company to withhold
shares from the shares of the Common Stock otherwise issuable to the participant
as a result of the exercise or acquisition of stock under the Stock Award; or
(3) delivering to the Company owned and unencumbered shares of the Common Stock
of the Company.

11.      CHANGE IN CONTROL.

         (a) In the event of a Change in Control, (i) any surviving or acquiring
corporation shall assume Stock Awards outstanding under the Plan or shall
substitute similar Stock Awards for those outstanding under the Plan, or (ii) in
the event any surviving or acquiring corporation refuses to assume such Stock
Awards or to substitute similar Stock Awards for those outstanding under the
Plan, (A) with respect to Stock Awards held by persons then performing services
as Employees, Directors or Consultants, the vesting of such Stock Awards
(including the lapse of any repurchase right held by the Company with respect to
shares acquired by such persons under a Stock Award) and the time during which
such Stock Awards may be exercised shall be accelerated prior to such event, and
the Stock Awards terminated if not exercised after such acceleration and at or
prior to such event, and (B) with respect to any other Stock Awards outstanding
under the Plan, such Stock Awards shall be terminated if not exercised prior to
such event.

         (b) With respect to any person who was providing services as an
Employee, Director or Consultant immediately prior to the consummation of a
Change in Control, any assumed Stock Awards or substitute stock awards held by
such persons shall immediately become fully vested and exercisable for the
longer of twelve (12) months following such full vesting or the expiration of
any applicable underwriters' lock-up agreements and thereafter shall terminate,
but such period shall not be longer than the term of the Option; and any
repurchase right held by the acquiring or surviving corporation with respect to
shares acquired by such persons under a Stock Award shall lapse, if such
person's Continuous Service is terminated by the surviving or acquiring
corporation other than for Cause, death or disability within the thirteen (13)
months following a Change in Control.

         (c) With respect to any person whose Continuous Service is terminated
by the Company, other than for Cause, death or disability, within the sixty (60)
days prior to a Change in Control, any Stock Awards held by such persons shall
immediately become fully vested and exercisable for the longer of twelve (12)
months following such full vesting or the expiration of any applicable
underwriters' lock-up agreements and thereafter shall terminate, but such period
shall not be longer than the term of the Option; and any repurchase right held
by the Company with respect to shares acquired by such persons under a Stock
Award shall lapse.


                                       10


<PAGE>   11
         (d) With respect to any persons whose Continuous Service is not
terminated prior to thirteen (13) months after a Change in Control, then any
Stock Awards held by such persons shall immediately become fully vested and
exercisable for the longer of twelve (12) months following such full vesting or
the expiration of any applicable underwriters' lock-up agreements and thereafter
shall terminate, but such period shall not be longer than the term of the
Option; and any repurchase right held by the Company with respect to shares
acquired by such persons under a Stock Award shall lapse.

         (e) For purposes of this Section 11 only, termination of Continuous
Service by the acquiring or surviving corporation following a Change in Control
shall include a termination of Continuous Service by a person upon thirty (30)
days written notice to the acquiring or surviving corporation that is due to any
one of the following actions being taken without such person's express written
consent: (i) material reduction in job responsibilities given the person's
position with the Company and the person's prior responsibilities with the
Company; (ii) any reduction in the person's annual base compensation as in
effect immediately prior to such reduction; (iii) relocation of the person's
workplace to a facility or location more than twenty-five (25) miles from the
person's workplace immediately prior to such relocation; or (iv) any purported
termination by the acquiring or surviving corporation which is not effected for
death, disability, or Cause; or for which the grounds relied upon are not valid.

         (f) Notwithstanding the foregoing, the terms of a Stock Award Agreement
may provide for different terms to govern events described in this Section 11.
In the event the provisions of this Section 11 conflict with an employment
agreement or other agreement relating to the rights of the holder of a Stock
Award, the provisions of this Section 11 and the conflicting agreement shall be
construed to provide the greatest benefit to the holder of the Stock Award.

         (g) For purposes of this Plan, "Change in Control" means: (1) a
dissolution, liquidation, or sale of all or substantially all of the assets of
the Company; (2) a merger or consolidation in which the Company is not the
surviving corporation; (3) a reverse merger in which the Company is the
surviving corporation but the shares of the Company's common shares outstanding
immediately preceding the merger are converted by virtue of the merger into
other property, whether in the form of securities, cash or otherwise; or (4) the
acquisition by any person, entity or group within the meaning of Section 13(d)
or 14(d) of the Exchange Act, or any comparable successor provisions (excluding
any employee benefit plan, or related trust, sponsored or maintained by the
Company or any Affiliate of the Company) of the beneficial ownership (within the
meaning of Rule 13d-3 promulgated under the Exchange Act, or comparable
successor rule) of securities of the Company representing at least fifty percent
(50%) of the combined voting power entitled to vote in the election of
directors.

12.      ADJUSTMENTS UPON CHANGES IN STOCK.

         If any change is made in the stock subject to the Plan, or subject to
any Stock Award, without the receipt of consideration by the Company (through
merger, consolidation, reorganization, recapitalization, reincorporation, stock
dividend, dividend in property other than cash, stock split, liquidating
dividend, combination of shares, exchange of shares, change in corporate
structure or other transaction not involving the receipt of consideration by the
Company), the Plan will be appropriately adjusted in the class(es) and maximum
number of 


                                       11


<PAGE>   12
shares subject to the Plan and the maximum number of shares subject to award to
any person during any calendar year, and the outstanding Stock Awards will be
appropriately adjusted in the class(es) and number of shares and price per share
of stock subject to such outstanding Stock Awards. Such adjustments shall be
made by the Board or Committee, the determination of which shall be final,
binding and conclusive. (The conversion of any convertible securities of the
Company shall not be treated as a "transaction not involving the receipt of
consideration by the Company.")

13.      AMENDMENT OF THE PLAN AND STOCK AWARDS.

         (a) The Board at any time, and from time to time, may amend the Plan.
However, except as provided in Section 11 relating to adjustments upon changes
in stock, no amendment shall be effective unless approved by the stockholders of
the Company to the extent stockholder approval is necessary for the Plan to
satisfy the requirements of Section 422 of the Code, Rule 16b-3 or any Nasdaq or
securities exchange listing requirements.

         (b) The Board may in its sole discretion submit any other amendment to
the Plan for stockholder approval, including, but not limited to, amendments to
the Plan intended to satisfy the requirements of Section 162(m) of the Code and
the regulations thereunder regarding the exclusion of performance-based
compensation from the limit on corporate deductibility of compensation paid to
certain executive officers.

         (c) It is expressly contemplated that the Board may amend the Plan in
any respect the Board deems necessary or advisable to provide eligible
Employees, Directors or Consultants with the maximum benefits provided or to be
provided under the provisions of the Code and the regulations promulgated
thereunder relating to Incentive Stock Options and/or to bring the Plan and/or
Incentive Stock Options granted under it into compliance therewith.

         (d) Rights and obligations under any Stock Award granted before
amendment of the Plan shall not be impaired by any amendment of the Plan unless
(i) the Company requests the consent of the person to whom the Stock Award was
granted and (ii) such person consents in writing.

         (e) The Board at any time, and from time to time, may amend the terms
of any one or more Stock Award; provided, however, that the rights and
obligations under any Stock Award shall not be impaired by any such amendment
unless (i) the Company requests the consent of the person to whom the Stock
Award was granted and (ii) such person consents in writing.

14.      TERMINATION OR SUSPENSION OF THE PLAN.

         (a) The Board may suspend or terminate the Plan at any time. Unless
sooner terminated, the Plan shall terminate ten (10) years from the date the
Plan is adopted by the Board or approved by the stockholders of the Company,
whichever is earlier. No Stock Awards may be granted under the Plan while the
Plan is suspended or after it is terminated.


                                       12


<PAGE>   13
         (b) Rights and obligations under any Stock Award granted while the Plan
is in effect shall not be impaired by suspension or termination of the Plan,
except with the consent of the person to whom the Stock Award was granted.

15.      STOCKHOLDER APPROVAL.

         No Stock Awards granted under the Plan shall be exercisable in whole or
part unless and until the Plan has been approved by the stockholders of the
Company, which approval shall be within twelve (12) months before or after the
date the Plan is adopted by the Board.


                                       13



<PAGE>   1
                                 RIBOGENE, INC.
                           1997 EQUITY INCENTIVE PLAN

                             STOCK OPTION AGREEMENT


      Pursuant to the Grant Notice and this Stock Option Agreement, the Company
has granted you an option to purchase the number of shares of the Company's
common stock ("Common Stock") indicated in the Grant Notice at the exercise
price indicated in the Grant Notice. Defined terms not explicitly defined in
this Stock Option Agreement but defined in the Plan shall have the same
definitions as in the Plan.

      The details of your option are as follows:

      1.    VESTING. Subject to the limitations contained herein, your option
will vest as provided in the Grant Notice, provided that vesting will cease upon
the termination of your Continuous Service.

      2.    METHOD OF PAYMENT.

            (a)   PAYMENT OPTIONS. Payment of the exercise price by cash or
check is due in full upon exercise of all or any part of your option, provided
that you may elect, to the extent permitted by applicable law and the Grant
Notice, to make payment of the exercise price under one of the following
alternatives:

                  (i)   Pursuant to a program developed under Regulation T as
promulgated by the Federal Reserve Board which, prior to the issuance of Common
Stock, results in either the receipt of cash (or check) by the Company or the
receipt of irrevocable instructions to pay the aggregate exercise price to the
Company from the sales proceeds;

                  (ii)  Provided that at the time of exercise the Company's
Common Stock is publicly traded and quoted regularly in The Wall Street Journal,
by delivery of already-owned shares of Common Stock, held for the period
required to avoid a charge to the Company's reported earnings, and owned free
and clear of any liens, claims, encumbrances or security interests, which Common
Stock shall be valued at its fair market value on the date of exercise; or

                  (iii) Payment by a combination of the above methods.

      3.    WHOLE SHARES. Your option may only be exercised for whole shares.

      4.    SECURITIES LAW COMPLIANCE. Notwithstanding anything to the contrary
contained herein, your option may not be exercised unless the shares issuable
upon exercise of your option are then registered under the Securities Act or, if
such shares are not then so registered, the Company has determined that such
exercise and issuance would be exempt from the registration requirements of the
Securities Act.


<PAGE>   2
      5.    TERM. The term of your option commences on the Date of Grant and
expires upon the earliest of:

                  (i)   the Expiration Date indicated in the Grant Notice;

                  (ii)  the tenth (10th) anniversary of the Date of Grant;

                  (iii) eighteen (18) months after your death, if you die
during, or within three (3) months after the termination of your Continuous
Service;

                  (iv)  twelve (12) months after the termination of your
Continuous Service due to disability;

                  (v)   the termination of your Continuous Service for Cause; or

                  (vi)  three (3) months after the termination of your
Continuous Service for any other reason, provided that if during any part of
such three (3)-month period the option is not exercisable solely because of the
condition set forth in paragraph 4 (Securities Law Compliance), in which event
the option shall not expire until the earlier of the Expiration Date or until it
shall have been exercisable for an aggregate period of three (3) months after
the termination of Continuous Service.

            For these purposes, "Cause" shall mean willful conduct that is
materially injurious to the Company (or any Affiliate) or any successor thereto,
whether financial or otherwise.

            To obtain the federal income tax advantages associated with an
"incentive stock option," the Code requires that at all times beginning on the
grant date of the option and ending on the day three (3) months before the date
of the option's exercise, you must be an employee of the Company, except in the
event of your death or permanent and total disability. The Company cannot
guarantee that your option will be treated as an "incentive stock option" if you
exercise your option more than three (3) months after the date your employment
with the Company terminates.

      6.    EXERCISE.

            (a)   You may exercise the vested portion of your option during its
term (and the unvested portion of your option if the Grant Notice so permits) by
delivering a Notice of Exercise (in the form attached to your Grant Notice or
other form designated by the Company) together with the exercise price to the
Secretary of the Company, or to such other person as the Company may designate,
during regular business hours, together with such additional documents as the
Company may then require.

            (b)   By exercising your option you agree that:

                  (i)   as a condition to any exercise of your option, the
Company may require you to enter an arrangement providing for the payment by you
to the Company of any tax withholding obligation of the Company arising by
reason of (1) the exercise of your 


                                       2
<PAGE>   3
option; (2) the lapse of any substantial risk of forfeiture to which the shares
are subject at the time of exercise; or (3) the disposition of shares acquired
upon such exercise;

                  (ii)  you will notify the Company in writing within fifteen
(15) days after the date of any disposition of any of the shares of the Common
Stock issued upon exercise of an incentive stock option that occurs within two
(2) years after the Date of Grant or within one (1) year after such shares of
Common Stock are transferred upon exercise of your option; and

                  (iii) the Company (or a representative of the underwriters)
may, in connection with the first underwritten registration of the offering of
any securities of the Company under the Act, require that you not sell or
otherwise transfer or dispose of any shares of Common Stock or other securities
of the Company during such period (not to exceed one hundred eighty (180) days)
following the effective date of the registration statement of the Company filed
under the Securities Act as may be requested by the Company or the
representative of the underwriters. You further agree that the Company may
impose stop-transfer instructions with respect to securities subject to the
foregoing restrictions until the end of such period.

      7.    TRANSFERABILITY. Your option is not transferable, except by will or
by the laws of descent and distribution, and is exercisable during your life
only by you. Notwithstanding the foregoing, by delivering written notice to the
Company, in a form satisfactory to the Company, you may designate a third party
who, in the event of your death, shall thereafter be entitled to exercise your
option.

      8.    OPTION NOT A SERVICE CONTRACT. Your option is not an employment
contract and nothing in your option shall be deemed to create in any way
whatsoever any obligation on your part to continue in the employ of the Company,
or of the Company to continue your employment with the Company. In addition,
nothing in your option shall obligate the Company, its shareholders, Board of
Directors, officers or employees to continue any relationship which you might
have as a Director or Consultant for the Company.

      9.    NOTICES. Any notices provided for in your option or the Plan shall
be given in writing and shall be deemed effectively given upon receipt or, in
the case of notices delivered by the Company to you, five (5) days after deposit
in the United States mail, postage prepaid, addressed to you at the last address
you provided to the Company.

      10.   GOVERNING PLAN DOCUMENT. Your option is subject to all the
provisions of the Plan, the provisions of which are hereby made a part of your
option, including without limitation the provisions of the Plan relating to
option provisions, and is further subject to all interpretations, amendments,
rules and regulations which may from time to time be promulgated and adopted
pursuant to the Plan. In the event of any conflict between the provisions of
your option and those of the Plan, the provisions of the Plan shall control.


                                       3

<PAGE>   1
                                 RIBOGENE, INC.

                        1997 EMPLOYEE STOCK PURCHASE PLAN

               ADOPTED BY THE BOARD OF DIRECTORS ON MARCH 8, 1998
                     APPROVED BY THE STOCKHOLDERS APRIL 1998


1.       PURPOSE.

         (a) The purpose of the 1997 Employee Stock Purchase Plan (the "Plan")
is to provide a means by which employees of RiboGene, Inc., a Delaware
corporation (the "Company"), and its Affiliates, as defined in subparagraph
1(b), which are designated as provided in subparagraph 2(b), may be given an
opportunity to purchase stock of the Company.

         (b) The word "Affiliate" as used in the Plan means any parent
corporation or subsidiary corporation of the Company, as those terms are defined
in Sections 424(e) and (f), respectively, of the Internal Revenue Code of 1986,
as amended (the "Code").

         (c) The Company, by means of the Plan, seeks to retain the services of
its employees, to secure and retain the services of new employees, and to
provide incentives for such persons to exert maximum efforts for the success of
the Company.

         (d) The Company intends that the rights to purchase stock of the
Company granted under the Plan be considered options issued under an "employee
stock purchase plan" as that term is defined in Section 423(b) of the Code.

2.       ADMINISTRATION.

         (a) The Plan shall be administered by the Board of Directors (the
"Board") of the Company unless and until the Board delegates administration to a
Committee, as provided in subparagraph 2(c). Whether or not the Board has
delegated administration, the Board shall have the final power to determine all
questions of policy and expediency that may arise in the administration of the
Plan.

         (b) The Board shall have the power, subject to, and within the
limitations of, the express provisions of the Plan:

                  (i) To determine when and how rights to purchase stock of the
Company shall be granted and the provisions of each offering of such rights
(which need not be identical).

                  (ii) To designate from time to time which Affiliates of the
Company shall be eligible to participate in the Plan.

                  (iii) To construe and interpret the Plan and rights granted
under it, and to establish, amend and revoke rules and regulations for its
administration. The Board, in the exercise of this power, may correct any
defect, omission or inconsistency in the Plan, in a manner and to the extent it
shall deem necessary or expedient to make the Plan fully effective.


<PAGE>   2
                  (iv) To amend the Plan as provided in paragraph 13.

                  (v) Generally, to exercise such powers and to perform such
acts as the Board deems necessary or expedient to promote the best interests of
the Company and its Affiliates and to carry out the intent that the Plan be
treated as an "employee stock purchase plan" within the meaning of Section 423
of the Code.

         (c) The Board may delegate administration of the Plan to a Committee
composed of two (2) or more members of the Board (the "Committee"). If
administration is delegated to a Committee, the Committee shall have, in
connection with the administration of the Plan, the powers theretofore possessed
by the Board, subject, however, to such resolutions, not inconsistent with the
provisions of the Plan, as may be adopted from time to time by the Board. The
Board may abolish the Committee at any time and revest in the Board the
administration of the Plan.

3.       SHARES SUBJECT TO THE PLAN.

         (a) Subject to the provisions of paragraph 12 relating to adjustments
upon changes in stock, the stock that may be sold pursuant to rights granted
under the Plan shall not exceed in the aggregate six hundred thousand (600,000)
shares of the Company's common stock (the "Common Stock"). If any right granted
under the Plan shall for any reason terminate without having been exercised, the
Common Stock not purchased under such right shall again become available for the
Plan.

         (b) The stock subject to the Plan may be unissued shares or reacquired
shares, bought on the market or otherwise.

4.       GRANT OF RIGHTS; OFFERING.

         (a) The Board or the Committee may from time to time grant or provide
for the grant of rights to purchase Common Stock of the Company under the Plan
to eligible employees (an "Offering") on a date or dates (the "Offering
Date(s)") selected by the Board or the Committee. Each Offering shall be in such
form and shall contain such terms and conditions as the Board or the Committee
shall deem appropriate, which shall comply with the requirements of Section
423(b)(5) of the Code that all employees granted rights to purchase stock under
the Plan shall have the same rights and privileges. The terms and conditions of
an Offering shall be incorporated by reference into the Plan and treated as part
of the Plan. The provisions of separate Offerings need not be identical, but
each Offering shall include (through incorporation of the provisions of this
Plan by reference in the document comprising the Offering or otherwise) the
period during which the Offering shall be effective, which period shall not
exceed twenty-seven (27) months beginning with the Offering Date, and the
substance of the provisions contained in paragraphs 5 through 8, inclusive.

         (b) If an employee has more than one right outstanding under the Plan,
unless he or she otherwise indicates in agreements or notices delivered
hereunder: (1) each agreement or notice delivered by that employee will be
deemed to apply to all of his or her rights under the Plan, and (2) a right with
a lower exercise price (or an earlier-granted right, if two rights have


                                       2


<PAGE>   3
identical exercise prices), will be exercised to the fullest possible extent
before a right with a higher exercise price (or a later-granted right, if two
rights have identical exercise prices) will be exercised.

5.       ELIGIBILITY.

         (a) Rights may be granted only to employees of the Company or, as the
Board or the Committee may designate as provided in subparagraph 2(b), to
employees of any Affiliate of the Company. Except as provided in subparagraph
5(b), an employee of the Company or any Affiliate shall not be eligible to be
granted rights under the Plan, unless, on the Offering Date, such employee has
been in the employ of the Company or any Affiliate for such continuous period
preceding such grant as the Board or the Committee may require, but in no event
shall the required period of continuous employment be equal to or greater than
two (2) years. In addition, unless otherwise determined by the Board or the
Committee and set forth in the terms of the applicable Offering, no employee of
the Company or any Affiliate shall be eligible to be granted rights under the
Plan, unless, on the Offering Date, such employee's customary employment with
the Company or such Affiliate is for at least twenty (20) hours per week and at
least five (5) months per calendar year.

         (b) The Board or the Committee may provide that each person who, during
the course of an Offering, first becomes an eligible employee of the Company or
designated Affiliate will, on a date or dates specified in the Offering which
coincides with the day on which such person becomes an eligible employee or
occurs thereafter, receive a right under that Offering, which right shall
thereafter be deemed to be a part of that Offering. Such right shall have the
same characteristics as any rights originally granted under that Offering, as
described herein, except that:

                  (i) the date on which such right is granted shall be the
"Offering Date" of such right for all purposes, including determination of the
exercise price of such right;

                  (ii) the period of the Offering with respect to such right
shall begin on its Offering Date and end coincident with the end of such
Offering; and

                  (iii) the Board or the Committee may provide that if such
person first becomes an eligible employee within a specified period of time
before the end of the Offering, he or she will not receive any right under that
Offering.

         (c) No employee shall be eligible for the grant of any rights under the
Plan if, immediately after any such rights are granted, such employee owns stock
possessing five percent (5%) or more of the total combined voting power or value
of all classes of stock of the Company or of any Affiliate. For purposes of this
subparagraph 5(c), the rules of Section 424(d) of the Code shall apply in
determining the stock ownership of any employee, and stock which such employee
may purchase under all outstanding rights and options shall be treated as stock
owned by such employee.

         (d) An eligible employee may be granted rights under the Plan only if
such rights, together with any other rights granted under "employee stock
purchase plans" of the Company 


                                       3


<PAGE>   4
and any Affiliates, as specified by Section 423(b)(8) of the Code, do not permit
such employee's rights to purchase stock of the Company or any Affiliate to
accrue at a rate which exceeds twenty-five thousand dollars ($25,000) of fair
market value of such stock (determined at the time such rights are granted) for
each calendar year in which such rights are outstanding at any time.

         (e) Officers of the Company and any designated Affiliate shall be
eligible to participate in Offerings under the Plan, provided, however, that the
Board may provide in an Offering that certain employees who are highly
compensated employees within the meaning of Section 423(b)(4)(D) of the Code
shall not be eligible to participate.

6.       RIGHTS; PURCHASE PRICE.

         (a) On each Offering Date, each eligible employee, pursuant to an
Offering made under the Plan, shall be granted the right to purchase up to the
number of shares of Common Stock of the Company purchasable with a percentage
designated by the Board or the Committee not exceeding fifteen percent (15%) of
such employee's Earnings (as defined in subparagraph 7(a)) during the period
which begins on the Offering Date (or such later date as the Board or the
Committee determines for a particular Offering) and ends on the date stated in
the Offering, which date shall be no later than the end of the Offering. The
Board or the Committee shall establish one or more dates during an Offering (the
"Purchase Date(s)") on which rights granted under the Plan shall be exercised
and purchases of Common Stock carried out in accordance with such Offering.

         (b) In connection with each Offering made under the Plan, the Board or
the Committee may specify a maximum number of shares that may be purchased by
any employee as well as a maximum aggregate number of shares that may be
purchased by all eligible employees pursuant to such Offering. In addition, in
connection with each Offering that contains more than one Purchase Date, the
Board or the Committee may specify a maximum aggregate number of shares which
may be purchased by all eligible employees on any given Purchase Date under the
Offering. If the aggregate purchase of shares upon exercise of rights granted
under the Offering would exceed any such maximum aggregate number, the Board or
the Committee shall make a pro rata allocation of the shares available in as
nearly a uniform manner as shall be practicable and as it shall deem to be
equitable.

         (c) The purchase price of stock acquired pursuant to rights granted
under the Plan shall be not less than the lesser of:

                  (i) an amount equal to eighty-five percent (85%) of the fair
market value of the stock on the Offering Date; or

                  (ii) an amount equal to eighty-five percent (85%) of the fair
market value of the stock on the Purchase Date.

7.       PARTICIPATION; WITHDRAWAL; TERMINATION.

         (a) An eligible employee may become a participant in the Plan pursuant
to an Offering by delivering a participation agreement to the Company within the
time specified in the 


                                       4


<PAGE>   5
Offering, in such form as the Company provides. Each such agreement shall
authorize payroll deductions of up to the maximum percentage specified by the
Board or the Committee of such employee's Earnings during the Offering.
"Earnings" is defined as an employee's regular salary or wages (including
amounts thereof elected to be deferred by the employee, that would otherwise
have been paid, under any arrangement established by the Company intended to
comply with Section 401(k), Section 402(e)(3), Section 125, Section 402(h), or
Section 403(b) of the Code, and also including any deferrals under a
non-qualified deferred compensation plan or arrangement established by the
Company), any may also include or exclude (as provided for each Offering) the
following items of compensation: bonuses, commissions, overtime pay, incentive
pay, profit sharing, other remuneration paid directly to the employee, the cost
of employee benefits paid for by the Company or an Affiliate, education or
tuition reimbursements, imputed income arising under any group insurance or
benefit program, traveling expenses, business and moving expense reimbursements,
income received in connection with stock options, contributions made by the
Company or an Affiliate under any employee benefit plan, and similar items of
compensation, as determined by the Board or Committee. The payroll deductions
made for each participant shall be credited to an account for such participant
under the Plan and shall be deposited with the general funds of the Company. A
participant may reduce (including to zero) or increase such payroll deductions,
and an eligible employee may begin such payroll deductions, after the beginning
of any Offering only as provided for in the Offering. A participant may make
additional payments into his or her account only if specifically provided for in
the Offering and only if the participant has not had the maximum amount withheld
during the Offering.

         (b) At any time during an Offering, a participant may terminate his or
her payroll deductions under the Plan and withdraw from the Offering by
delivering to the Company a notice of withdrawal in such form as the Company
provides. Such withdrawal may be elected at any time prior to the end of the
Offering except as provided by the Board or the Committee in the Offering. Upon
such withdrawal from the Offering by a participant, the Company shall distribute
to such participant all of his or her accumulated payroll deductions (reduced to
the extent, if any, such deductions have been used to acquire stock for the
participant) under the Offering, without interest, and such participant's
interest in that Offering shall be automatically terminated. A participant's
withdrawal from an Offering will have no effect upon such participant's
eligibility to participate in any other Offerings under the Plan but such
participant will be required to deliver a new participation agreement in order
to participate in subsequent Offerings under the Plan.

         (c) Rights granted pursuant to any Offering under the Plan shall
terminate immediately upon cessation of a participant's employment with the
Company and any designated Affiliate, for any reason, and the Company shall
distribute to such terminated employee all of his or her accumulated payroll
deductions (reduced to the extent, if any, such deductions have been used to
acquire stock for the terminated employee), under the Offering, without
interest.

         (d) Rights granted under the Plan shall not be transferable by a
participant otherwise than by will or the laws of descent and distribution, or
by a beneficiary designation as provided in paragraph 14 and, otherwise during
his or her lifetime, shall be exercisable only by the person to whom such rights
are granted.


                                       5


<PAGE>   6
8.       EXERCISE.

         (a) On each Purchase Date specified in the relevant Offering, each
participant's accumulated payroll deductions and other additional payments
specifically provided for in the Offering (without any increase for interest)
will be applied to the purchase of whole shares of stock of the Company, up to
the maximum number of shares permitted pursuant to the terms of the Plan and the
applicable Offering, at the purchase price specified in the Offering. No
fractional shares shall be issued upon the exercise of rights granted under the
Plan, unless the Offering document specifically provides otherwise. The amount,
if any, of accumulated payroll deductions remaining in each participant's
account after the purchase of shares which is less than the amount required to
purchase one share of stock on the final Purchase Date of an Offering shall be
held in each such participant's account for the purchase of shares under the
next Offering under the Plan, unless such participant withdraws from such next
Offering, as provided in subparagraph 7(b), or is no longer eligible to be
granted rights under the Plan, as provided in paragraph 5, in which case such
amount shall be distributed to the participant after such final Purchase Date,
without interest. The amount, if any, of accumulated payroll deductions
remaining in any participant's account after the purchase of shares which is
equal to the amount required to purchase whole shares of stock on the final
Purchase Date of an Offering shall be distributed in full to the participant
after such Purchase Date, without interest.

         (b) No rights granted under the Plan may be exercised to any extent
unless the shares to be issued upon such exercise under the Plan (including
rights granted thereunder) are covered by an effective registration statement
pursuant to the Securities Act of 1933, as amended (the "Securities Act") and
the Plan is in material compliance with all applicable state, foreign and other
securities and other laws applicable to the Plan. If on a Purchase Date in any
Offering hereunder the Plan is not so registered or in such compliance, no
rights granted under the Plan or any Offering shall be exercised on such
Purchase Date, and the Purchase Date shall be delayed until the Plan is subject
to such an effective registration statement and such compliance, except that the
Purchase Date shall not be delayed more than twelve (12) months and the Purchase
Date shall in no event be more than twenty-seven (27) months from the Offering
Date. If on the Purchase Date of any Offering hereunder, as delayed to the
maximum extent permissible, the Plan is not registered and in such compliance,
no rights granted under the Plan or any Offering shall be exercised and all
payroll deductions accumulated during the Offering (reduced to the extent, if
any, such deductions have been used to acquire stock) shall be distributed to
the participants, without interest.

9.       COVENANTS OF THE COMPANY.

         (a) During the terms of the rights granted under the Plan, the Company
shall keep available at all times the number of shares of stock required to
satisfy such rights.

         (b) The Company shall seek to obtain from each federal, state, foreign
or other regulatory commission or agency having jurisdiction over the Plan such
authority as may be required to issue and sell shares of stock upon exercise of
the rights granted under the Plan. If, after reasonable efforts, the Company is
unable to obtain from any such regulatory commission or agency the authority
which counsel for the Company deems necessary for the lawful issuance 


                                       6


<PAGE>   7
and sale of stock under the Plan, the Company shall be relieved from any
liability for failure to issue and sell stock upon exercise of such rights
unless and until such authority is obtained.

10.      USE OF PROCEEDS FROM STOCK.

         Proceeds from the sale of stock pursuant to rights granted under the
Plan shall constitute general funds of the Company.

11.      RIGHTS AS A STOCKHOLDER.

         A participant shall not be deemed to be the holder of, or to have any
of the rights of a holder with respect to, any shares subject to rights granted
under the Plan unless and until the participant's shares acquired upon exercise
of rights hereunder are recorded in the books of the Company.

12.      ADJUSTMENTS UPON CHANGES IN STOCK.

         (a) If any change is made in the stock subject to the Plan, or subject
to any rights granted under the Plan (through merger, consolidation,
reorganization, recapitalization, stock dividend, dividend in property other
than cash, stock split, liquidating dividend, combination of shares, exchange of
shares, change in corporate structure or other transaction not involving the
receipt of consideration by the Company), the Plan and outstanding rights will
be appropriately adjusted in the class(es) and maximum number of shares subject
to the Plan and the class(es) and number of shares and price per share of stock
subject to outstanding rights. Such adjustments shall be made by the Board or
the Committee, the determination of which shall be final, binding and
conclusive. (The conversion of any convertible securities of the Company shall
not be treated as a "transaction not involving the receipt of consideration by
the Company.")

         (b) In the event of: (1) a dissolution or liquidation of the Company;
(2) a merger or consolidation in which the Company is not the surviving
corporation; (3) a reverse merger in which the Company is the surviving
corporation but the shares of the Company's Common Stock outstanding immediately
preceding the merger are converted by virtue of the merger into other property,
whether in the form of securities, cash or otherwise; or (4) the acquisition by
any person, entity or group within the meaning of Section 13(d) or 14(d) of the
Securities Exchange Act of 1934, as amended (the "Exchange Act") or any
comparable successor provisions (excluding any employee benefit plan, or related
trust, sponsored or maintained by the Company or any Affiliate of the Company)
of the beneficial ownership (within the meaning of Rule 13d-3 promulgated under
the Exchange Act, or comparable successor rule) of securities of the Company
representing at least fifty percent (50%) of the combined voting power entitled
to vote in the election of directors, then, as determined by the Board in its
sole discretion (i) any surviving or acquiring corporation may assume
outstanding rights or substitute similar rights for those under the Plan, (ii)
such rights may continue in full force and effect, or (iii) participants'
accumulated payroll deductions may be used to purchase Common Stock immediately
prior to the transaction described above and the participants' rights under the
ongoing Offering terminated.


                                       7


<PAGE>   8
13.      AMENDMENT OF THE PLAN.

         (a) The Board at any time, and from time to time, may amend the Plan.
However, except as provided in paragraph 12 relating to adjustments upon changes
in stock, no amendment shall be effective unless approved by the stockholders of
the Company within twelve (12) months before or after the adoption of the
amendment if such amendment requires stockholder approval in order for the Plan
to obtain employee stock purchase plan treatment under Section 423 of the Code
or to comply with the requirements of Rule 16b-3 promulgated under the Exchange
Act or any Nasdaq or securities exchange requirements.

         (b) The Board may amend the Plan in any respect the Board deems
necessary or advisable to provide eligible employees with the maximum benefits
provided or to be provided under the provisions of the Code and the regulations
promulgated thereunder relating to employee stock purchase plans and/or to bring
the Plan and/or rights granted under it into compliance therewith.

         (c) Rights and obligations under any rights granted before amendment of
the Plan shall not be altered or impaired by any amendment of the Plan, except
with the consent of the person to whom such rights were granted, or except as
necessary to comply with any laws or governmental regulations, or except as
necessary to ensure that the Plan and/or rights granted under the Plan comply
with the requirements of Section 423 of the Code.

14.      DESIGNATION OF BENEFICIARY.

         (a) A participant may file a written designation of a beneficiary who
is to receive any shares and cash, if any, from the participant's account under
the Plan in the event of such participant's death subsequent to the end of an
Offering but prior to delivery to the participant of such shares and cash. In
addition, a participant may file a written designation of a beneficiary who is
to receive any cash from the participant's account under the Plan in the event
of such participant's death during an Offering.

         (b) Such designation of beneficiary may be changed by the participant
at any time by written notice. In the event of the death of a participant and in
the absence of a beneficiary validly designated under the Plan who is living at
the time of such participant's death, the Company shall deliver such shares
and/or cash to the executor or administrator of the estate of the participant,
or if no such executor or administrator has been appointed (to the knowledge of
the Company), the Company, in its sole discretion, may deliver such shares
and/or cash to the spouse or to any one or more dependents or relatives of the
participant, or if no spouse, dependent or relative is known to the Company,
then to such other person as the Company may designate.

15.      TERMINATION OR SUSPENSION OF THE PLAN.

         (a) The Board in its discretion, may suspend or terminate the Plan at
any time. No rights may be granted under the Plan while the Plan is suspended or
after it is terminated.


                                       8


<PAGE>   9
         (b) Rights and obligations under any rights granted while the Plan is
in effect shall not be altered or impaired by suspension or termination of the
Plan, except as expressly provided in the Plan or with the consent of the person
to whom such rights were granted, or except as necessary to comply with any laws
or governmental regulation, or except as necessary to ensure that the Plan
and/or rights granted under the Plan comply with the requirements of Section 423
of the Code.

16.      EFFECTIVE DATE OF PLAN.

         The Plan shall become effective upon the Company's initial public
offering of shares of common stock (the "Effective Date"), but no rights granted
under the Plan shall be exercised unless and until the Plan has been approved by
the stockholders of the Company within twelve (12) months before or after the
date the Plan is adopted by the Board or the Committee, which date may be prior
to the Effective Date.


                                       9



<PAGE>   1
                                 RIBOGENE, INC.

                 1997 NON-EMPLOYEE DIRECTORS' STOCK OPTION PLAN

               ADOPTED BY THE BOARD OF DIRECTORS ON MARCH 8, 1998
                       APPROVED BY STOCKHOLDERS APRIL 1998


1.    PURPOSE.

      (a)   The purpose of the 1997 Non-Employee Directors' Stock Option Plan
(the "Plan") is to provide a means by which each director of RiboGene, Inc. (the
"Company") who is not otherwise at the time of grant an employee of or
consultant to the Company or of any Affiliate of the Company (each such person
being hereafter referred to as a "Non-Employee Director") will be given an
opportunity to purchase stock of the Company.

      (b)   The word "Affiliate" as used in the Plan means any parent
corporation or subsidiary corporation of the Company as those terms are defined
in Sections 424(e) and (f), respectively, of the Internal Revenue Code of 1986,
as amended from time to time (the "Code").

      (c)   The Company, by means of the Plan, seeks to retain the services of
persons now serving as Non-Employee Directors of the Company, to secure and
retain the services of persons capable of serving in such capacity, and to
provide incentives for such persons to exert maximum efforts for the success of
the Company.

2.    ADMINISTRATION.

      (a)   The Plan shall be administered by the Board of Directors of the
Company (the "Board") unless and until the Board delegates administration to a
committee, as provided in subparagraph 2(b).

      (b)   The Board may delegate administration of the Plan to a committee
composed of two (2) or more members of the Board (the "Committee"). If
administration is delegated to a Committee, the Committee shall have, in
connection with the administration of the Plan, the powers theretofore possessed
by the Board, subject, however, to such resolutions, not inconsistent with the
provisions of the Plan, as may be adopted from time to time by the Board. The
Board may abolish the Committee at any time and revest in the Board the
administration of the Plan.

3.    SHARES SUBJECT TO THE PLAN.

      (a)   Subject to the provisions of paragraph 10 relating to adjustments
upon changes in stock, the stock that may be sold pursuant to options granted
under the Plan shall not exceed in the aggregate eighty thousand (80,000) shares
of the Company's common stock. If any option granted under the Plan shall for
any reason expire or otherwise terminate without having been exercised in full,
the stock not purchased under such option shall again become available for the
Plan.


<PAGE>   2
      (b)   The stock subject to the Plan may be unissued shares or reacquired
shares, bought on the market or otherwise.

4.    ELIGIBILITY.

      Options shall be granted only to Non-Employee Directors of the Company.

5.    NON-DISCRETIONARY GRANTS.

      (a)   Each person who is first elected or appointed to the Board as a
Non-Employee Director after the Adoption Date shall automatically be granted, on
the date of such initial election or appointment, an option to purchase ten
thousand (10,000) shares of common stock of the Company on the terms and
conditions set forth herein (hereinafter, an "Initial Grant").

      (b)   Each Non-Employee Director who is serving as a Non-Employee Director
immediately following each annual meeting of stockholders, commencing with the
annual meeting of stockholders in calendar year 1998, and who has continuously
served as a Non-Employee Director for the six (6)-month period prior to the date
of the such annual meeting of stockholders, shall automatically be granted, on
such date, an option to purchase two thousand five hundred (2,500) shares of
common stock of the Company on the terms and conditions set forth herein
(hereinafter, an "Annual Grant").

6.    OPTION PROVISIONS.

      Each option shall be subject to the following terms and conditions:

      (a)   The term of each option commences on the date it is granted and,
unless sooner terminated as set forth herein, expires on the date ("Expiration
Date") ten (10) years from the date of grant. If the optionee's service as a
Non-Employee Director or employee of or consultant to the Company or any
Affiliate terminates for any reason or for no reason, the option shall terminate
on the earlier of the Expiration Date or the date twelve (12) months following
the date of termination of all such service; provided, however, that if such
termination of service is due to the optionee's death, the option shall
terminate on the earlier of the Expiration Date or eighteen (18) months
following the date of the optionee's death. In any and all circumstances, an
option may be exercised following termination of the optionee's service as a
Non-Employee Director or employee of or consultant to the Company or any
Affiliate only as to that number of shares as to which it was exercisable as of
the date of termination of all such service under the provisions of subparagraph
6(e).

      (b)   The exercise price of each option shall be equal to one hundred
percent (100%) of the Fair Market Value of the stock (as such term is defined in
subsection 9(e) of this Plan) subject to such option on the date such option is
granted.

      (c)   The optionee may elect to make payment of the exercise price under
one of the following alternatives:

            (i)   In cash (or check) at the time of exercise;


                                       2
<PAGE>   3
            (ii)  Provided that at the time of the exercise the Company's common
stock is publicly traded and quoted regularly in The Wall Street Journal,
payment by delivery of shares of common stock of the Company already owned by
the optionee, held for the period required to avoid a charge to the Company's
reported earnings, and owned free and clear of any liens, claims, encumbrances
or security interest, which common stock shall be valued at its Fair Market
Value on the date immediately preceding the date of exercise; or

            (iii) Pursuant to a program developed under Regulation T as
promulgated by the Federal Reserve Board which results in the receipt of cash
(or check) by the Company either prior to the issuance of shares of the
Company's common stock or pursuant to the terms of irrevocable instructions
issued by the optionee prior to the issuance of shares of the Company's common
stock.

            (iv)  Payment by a combination of the methods of payment specified
in subparagraph 6(c)(i) through 6(c)(iii) above.

      (d)   An option shall be transferable only to the extent specifically
provided in the option agreement; provided, however, that if the option
agreement does not specifically provide for the transferability of an option,
then the option shall not be transferable except by will or by the laws of
descent and distribution, and shall be exercisable during the lifetime of the
person to whom the option is granted only by such person (or by his guardian or
legal representative) or transferee pursuant to such an order. Notwithstanding
the foregoing, the optionee may, by delivering written notice to the Company in
a form satisfactory to the Company, designate a third party who, in the event of
the death of the optionee, shall thereafter be entitled to exercise the option.

      (e)   (i) An Initial Grant shall become exercisable in four (4) equal
annual installments measured from the date of grant, commencing on the one
(1)-year anniversary of the date of grant of the option, and (ii) an Annual
Grant shall become exercisable one (1) year from the date of grant, provided
that, with respect to any grant under the Plan, the optionee has, during the
entire period prior to such vesting installment date, continuously served as a
Non-Employee Director or employee of or consultant to the Company or any
Affiliate of the Company, whereupon such option shall become fully exercisable
in accordance with its terms with respect to that portion of the shares
represented by that installment.

      (f)   The Company may require any optionee, or any person to whom an
option is transferred under subparagraph 6(d), as a condition of exercising any
such option: (i) to give written assurances satisfactory to the Company as to
the optionee's knowledge and experience in financial and business matters; and
(ii) to give written assurances satisfactory to the Company stating that such
person is acquiring the stock subject to the option for such person's own
account and not with any present intention of selling or otherwise distributing
the stock. These requirements, and any assurances given pursuant to such
requirements, shall be inoperative if (x) the issuance of the shares upon the
exercise of the option has been registered under a then currently-effective
registration statement under the Securities Act of 1933, as amended (the
"Securities Act"), or (y) as to any particular requirement, a determination is
made by counsel for the Company that such requirement need not be met in the
circumstances under the then applicable securities laws. The Company may require
any optionee to provide such other 


                                       3
<PAGE>   4
representations, written assurances or information which the Company shall
determine is necessary, desirable or appropriate to comply with applicable
securities laws as a condition of granting an option to the optionee or
permitting the optionee to exercise the option. The Company may, upon advice of
counsel to the Company, place legends on stock certificates issued under the
Plan as such counsel deems necessary or appropriate in order to comply with
applicable securities laws, including, but not limited to, legends restricting
the transfer of the stock.

      (g)   Notwithstanding anything to the contrary contained herein, an option
may not be exercised unless the shares issuable upon exercise of such option are
then registered under the Securities Act or, if such shares are not then so
registered, the Company has determined that such exercise and issuance would be
exempt from the registration requirements of the Securities Act.

7.    COVENANTS OF THE COMPANY.

      (a)   During the terms of the options granted under the Plan, the Company
shall keep available at all times the number of shares of stock required to
satisfy such options.

      (b)   The Company shall seek to obtain from each regulatory commission or
agency having jurisdiction over the Plan such authority as may be required to
issue and sell shares of stock upon exercise of the options granted under the
Plan; provided however, that this undertaking shall not require the Company to
register under the Securities Act either the Plan, any option granted under the
Plan, or any stock issued or issuable pursuant to any such option. If, after
reasonable efforts, the Company is unable to obtain from any such regulatory
commission or agency the authority which counsel for the Company deems necessary
for the lawful issuance and sale of stock under the Plan, the Company shall be
relieved from any liability for failure to issue and sell stock upon exercise of
such options.

8.    USE OF PROCEEDS FROM STOCK.

      Proceeds from the sale of stock pursuant to options granted under the Plan
shall constitute general funds of the Company.

9.    MISCELLANEOUS.

      (a)   Neither an optionee nor any person to whom an option is transferred
under subparagraph 6(d) shall be deemed to be the holder of, or to have any of
the rights of a holder with respect to, any shares subject to such option unless
and until such person has satisfied all requirements for exercise of the option
pursuant to its terms.

      (b)   Nothing in the Plan or in any instrument executed pursuant thereto
shall confer upon any Non-Employee Director any right to continue in the service
of the Company or any Affiliate in any capacity or shall affect any right of the
Company, its Board or stockholders or any Affiliate, to remove any Non-Employee
Director pursuant to the Company's Bylaws and the provisions of Delaware General
Corporations Law.


                                       4
<PAGE>   5
      (c)   No Non-Employee Director, individually or as a member of a group,
and no beneficiary or other person claiming under or through him, shall have any
right, title or interest in or to any option reserved for the purposes of the
Plan except as to such shares of common stock, if any, as shall have been
reserved for him pursuant to an option granted to him.

      (d)   In connection with each option made pursuant to the Plan, it shall
be a condition precedent to the Company's obligation to issue or transfer shares
to a Non-Employee Director, or to evidence the removal of any restrictions on
transfer, that such Non-Employee Director make arrangements satisfactory to the
Company to insure that the amount of any federal, state or local withholding tax
required to be withheld with respect to such sale or transfer, or such removal
or lapse, is made available to the Company for timely payment of such tax.

      (e)   As used in this Plan, "Fair Market Value" means, as of any date, the
value of the common stock of the Company determined as follows:

            (i)   If the common stock is listed on any established stock
exchange or a national market system, including without limitation the Nasdaq
National Market or The Nasdaq SmallCap, the Fair Market Value of a share of
common stock shall be the closing sales price for such stock (or the closing
bid, if no sales were reported) as quoted on such system or exchange (or the
exchange with the greatest volume of trading in common stock) on the last market
trading day prior to the day of determination, as reported in The Wall Street
Journal or such other source as the Board deems reliable; or

            (ii)  In the absence of an established market for the common stock,
the Fair Market Value shall be determined in good faith by the Board.

10.   ADJUSTMENTS UPON CHANGES IN STOCK.

      (a)   If any change is made in the stock subject to the Plan, or subject
to any option granted under the Plan (through merger, consolidation,
reorganization, recapitalization, stock dividend, dividend in property other
than cash, stock split, liquidating dividend, combination of shares, exchange of
shares, change in corporate structure or other transaction not involving the
receipt of consideration by the Company), the Plan and outstanding options will
be appropriately adjusted in the class(es) and maximum number of shares subject
to the Plan and the class(es) and number of shares and price per share of stock
subject to outstanding options. Such adjustments shall be made by the Board, the
determination of which shall be final, binding and conclusive. (The conversion
of any convertible securities of the Company shall not be treated as a
"transaction not involving the receipt of consideration by the Company.")

      (b)   In the event of: (1) a dissolution, liquidation, or sale of all or
substantially all of the assets of the Company; (2) a merger or consolidation in
which the Company is not the surviving corporation; (3) a reverse merger in
which the Company is the surviving corporation but the shares of the Company's
common stock outstanding immediately preceding the merger are converted by
virtue of the merger into other property, whether in the form of securities,
cash or otherwise; or (4) the acquisition by any person, entity or group within
the meaning of Section 13(d) or 14(d) of the Securities Exchange Act of 1934, as
amended (the "Exchange Act") or any comparable successor provisions (excluding
any employee benefit plan, or related trust, 


                                       5
<PAGE>   6
sponsored or maintained by the Company or any Affiliate of the Company) of the
beneficial ownership (within the meaning of Rule 13d-3 promulgated under the
Exchange Act, or comparable successor rule) of securities of the Company
representing at least fifty percent (50%) of the combined voting power entitled
to vote in the election of directors, then to the extent not prohibited by
applicable law, the time during which options outstanding under the Plan may be
exercised shall be accelerated prior to such event and the options terminated if
not exercised after such acceleration and at or prior to such event.

11.   AMENDMENT OF THE PLAN.

      (a)   The Board at any time, and from time to time, may amend the Plan
and/or some or all outstanding options granted under the Plan. However, except
as provided in paragraph 10 relating to adjustments upon changes in stock, no
amendment shall be effective unless approved by the stockholders of the Company
to the extent stockholder approval is necessary for the Plan to satisfy the
requirements of Rule 16b-3 promulgated under the Exchange Act or any Nasdaq or
securities exchange listing requirements.

      (b)   Rights and obligations under any option granted before any amendment
of the Plan shall not be impaired by such amendment unless (i) the Company
requests the consent of the person to whom the option was granted and (ii) such
person consents in writing.

12.   TERMINATION OR SUSPENSION OF THE PLAN.

      (a)   The Board may suspend or terminate the Plan at any time. Unless
sooner terminated, the Plan shall terminate on March 8, 2008. No options may be
granted under the Plan while the Plan is suspended or after it is terminated.

      (b)   Rights and obligations under any option granted while the Plan is in
effect shall not be impaired by suspension or termination of the Plan, except
with the consent of the person to whom the option was granted.

      (c)   The Plan shall terminate upon the occurrence of any of the events
described in Section 10(b) above.

13.   EFFECTIVE DATE OF PLAN; CONDITIONS OF EXERCISE.

      (a)   The Plan shall become effective upon adoption by the Board.

      (b)   No option granted under the Plan shall be exercised or become
exercisable unless and until the Plan is approved by the stockholders of the
Company.


                                       6

<PAGE>   1
                                 RIBOGENE, INC.
                 1997 NON-EMPLOYEE DIRECTORS' STOCK OPTION PLAN

                            NONSTATUTORY STOCK OPTION


_________________________, Optionee:

      On __________________, 19___, an option was automatically granted to you
(the "Optionee") pursuant to the Ribogene, Inc. (the "Company") 1997
Non-Employee Directors' Stock Option Plan (the "Plan") to purchase shares of the
Company's common stock ("Common Stock"). This option is not intended to qualify
and will not be treated as an "incentive stock option" within the meaning of
Section 422 of the Internal Revenue Code of 1986, as amended (the "Code").

      The grant hereunder is in connection with and in furtherance of the
Company's compensatory benefit plan for Non-Employee Directors (as defined in
the Plan).

      The details of your option are as follows:

      1.    The total number of shares of Common Stock subject to this option is
[_____________________________ ( )].

      2.    The exercise price of this option is _____________________
($________) per share, such amount being equal to the Fair Market Value (as
defined in the Plan) of the Common Stock on the date of grant of this option.

      3.    (a)   Subject to the limitations contained herein, if:

                  (i)   this option is exercisable for 10,000 shares, then this
option shall become exercisable (i.e., vest) in four (4) equal annual
installments with the first installment becoming exercisable one (1) year after
the date of grant; or

                  (ii)  this option is exercisable for 2,500 shares, then this
option shall become exercisable (i.e., vest) one (1) year after the date of
grant;

provided, however, that you have, during the period from the date of grant to
such vesting date, continuously served as a Non-Employee Director or employee of
or consultant to the Company or any Affiliate (as defined in the Plan),
whereupon this option shall become fully exercisable with respect to that
portion of the shares represented by that installment.

            (b)   Notwithstanding anything to the foregoing, this option shall
not be exercisable in whole or in part unless and until the Plan has been
approved by the Company's stockholders.

      4.    (a)   This option may be exercised, to the extent specified above,
by delivering a Notice of Exercise (in the form attached hereto or such other
form designated by the Company) together with the exercise price to the
Secretary of the Company, or to such other person as the Company may designate,
during regular business hours, together with such additional documents as the
Company may then require pursuant to Section 6 of the Plan.

            (b)   This option may only be exercised for whole shares.

            (c)   You may elect to pay the exercise price under one of the
following alternatives:

                  (i)   In cash (or check) at the time of exercise;


<PAGE>   2
                  (ii)  Provided that at the time of the exercise the Common
Stock is publicly traded and quoted regularly in The Wall Street Journal,
payment by delivery of shares of Common Stock already owned by you, held for the
period required to avoid a charge to the Company's reported earnings, and owned
free and clear of any liens, claims, encumbrances or security interest, which
Common Stock shall be valued at its Fair Market Value on the date immediately
preceding the date of exercise; or

                  (iii) Payment pursuant to a program developed under Regulation
T as promulgated by the Federal Reserve Board which results in the receipt of
cash (or check) by the Company either prior to the issuance of shares of the
Common Stock or pursuant to the terms of irrevocable instructions issued by you
prior to the issuance of shares of the Common Stock.

                  (iv)  Payment by a combination of the methods of payment
specified in subparagraphs (i) through (iii) above.

            (d)   By exercising this option you agree that the Company may
require you to enter an arrangement providing for the cash payment by you to the
Company of any tax withholding obligation of the Company arising by reason of
the exercise of this option.

      5.    The term of this option is ten (10) years measured from the date of
grant, subject, however, to earlier termination upon your termination of
service, as set forth in Section 6(a) of the Plan.

      6.    Any notices provided for in this option or the Plan shall be given
in writing and shall be deemed effectively given upon receipt or, in the case of
notices delivered by the Company to you, five (5) days after deposit in the
United States mail, postage prepaid, addressed to you at the address specified
below or at such other address as you hereafter designate by written notice to
the Company.

      7.    This option is subject to all the provisions of the Plan, a copy of
which is attached hereto and its provisions are hereby made a part of this
option, including without limitation the provisions of Section 6 of the Plan
relating to option provisions, and is further subject to all interpretations,
amendments, rules and regulations which may from time to time be promulgated and
adopted pursuant to the Plan. In the event of any conflict between the
provisions of this option and those of the Plan, the provisions of the Plan
shall control.

      Dated the ____ day of _______________, 19__.

                                       Very truly yours,
                                       RIBOGENE, INC.



                                       Duly authorized on behalf
                                       of the Board of Directors

ATTACHMENTS:  Notice of Exercise
              Prospectus-1997 Non-Employee Directors' Stock Option Plan


                                       2
<PAGE>   3
The undersigned:

      (a)   Acknowledges receipt of the foregoing option and the attachments
referenced therein and understands that all rights and liabilities with respect
to this option are set forth in the option and the Plan; and

      (b)   Acknowledges that as of the date of grant of this option, it sets
forth the entire understanding between the undersigned Optionee and the Company
and its Affiliates regarding the acquisition of Common Stock in the Company and
supersedes all prior oral and written agreements on that subject with the
exception of (i) the options and any other stock awards previously granted and
delivered to the undersigned under stock award plans of the Company, and (ii)
the following agreements only:


            NONE: _____________________
                  (Initial)

            OTHER:   __________________________________________
                     __________________________________________
                     __________________________________________




                                    Optionee



                                       3

<PAGE>   4
                                 RIBOGENE, INC.
                 1997 NON-EMPLOYEE DIRECTORS' STOCK OPTION PLAN

                               NOTICE OF EXERCISE


Ribogene, Inc.

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


Ladies and Gentlemen:

      This constitutes notice under my stock option that I elect to purchase the
number of shares for the price set forth below.

      Type of option:                       Nonstatutory

      Stock option dated:                   ___________________

      Number of shares for 
      which option is exercised:            ___________________

      Certificates to be
      issued in name of:                    ___________________

      Total exercise price:                 $__________________

      Cash payment delivered
      herewith:                             $__________________

      Value of ______ shares of
      common stock delivered herewith(1):   $__________________


      By this exercise, I agree (i) to provide such additional documents as you
may require pursuant to the terms of the Company's 1997 Non-Employee Directors'
Stock Option Plan and (ii) to provide for the payment by me to you (in the
manner designated by you) of your withholding obligation, if any, relating to
the exercise of this option.

                                       Very truly yours,



                                       _________________________________________
                                       Optionee



- ----------------
1     Shares must meet the public trading requirements set forth in the option.
Shares must be valued in accordance with the terms of the option being
exercised, must have been owned for the minimum period required in the option,
and must be owned free and clear of any liens, claims, encumbrances or security
interests. Certificates must be endorsed or accompanied by an executed
assignment separate from certificate.


                                       1


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