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                                                                   EXHIBIT 99.1

                        IDEC PHARMACEUTICALS CORPORATION
                             1988 STOCK OPTION PLAN

                    AMENDED AND RESTATED THROUGH MAY 22, 1997


       I.      PURPOSES OF THE PLAN

               (a)  This Stock Option Plan (the "Plan") is intended to promote
the interests of IDEC Pharmaceuticals Corporation, a Delaware corporation (the
"Corporation"), by providing a method whereby (i) key employees (including
officers and directors) of the Corporation (or its parent or subsidiary
corporations) responsible for the management, growth and financial success of
the Corporation (or its parent or subsidiary corporations), (ii) the
non-employee members of the Corporation's Board of Directors (or any parent or
subsidiary corporations) and (iii) independent consultants and advisors who
provide valuable services to the Corporation (or its parent or subsidiary
corporations) may be offered incentives and rewards which will encourage them to
acquire a proprietary interest, or otherwise increase their proprietary
interest, in the Corporation and continue to render services to the Corporation
(or its parent or subsidiary corporations).

               (b)  The following provisions shall be applicable in determining
the parent and subsidiary corporations of the Corporation:

                    (i)  Any corporation (other than the Corporation) in an
unbroken chain of corporations ending with the Corporation shall be considered
to be a PARENT corporation of the Corporation, provided each such corporation in
the unbroken chain (other than the Corporation) owns, at the time of the
determination, stock possessing fifty percent (50%) or more of the total
combined voting power of all classes of stock in one of the other corporations
in such chain.

                   (ii)  Each corporation (other than the Corporation) in an
unbroken chain of corporations beginning with the Corporation shall be
considered to be a SUBSIDIARY of the Corporation, provided each such corporation
(other than the last corporation) in the unbroken chain owns, at the time of the
determination, stock possessing fifty percent (50%) or more of the total
combined voting power of all classes of stock in one of the other corporations
in such chain.

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     II.       ADMINISTRATION OF THE PLAN

               (a)    The Corporation's Board of Directors (the "Board") shall
appoint a committee ("Committee") of two (2) or more non-employee Board members
to assume full responsibility for the administration of the Plan. Members of the
Committee shall serve for such period of time as the Board may determine and
shall be subject to removal by the Board at any time.

               (b)    The Committee as Plan Administrator shall have full power 
and authority (subject to the express provisions of the Plan) to establish such
rules and regulations as it may deem appropriate for the proper administration
of the Plan and to make such determinations under, and issue such
interpretations of, the Plan and any outstanding option grants or stock
issuances as it may deem necessary or advisable. Decisions of the Plan
Administrator shall be final and binding on all parties who have an interest in
the Plan or any outstanding option or stock issuance thereunder.

     III.      ELIGIBILITY FOR OPTION GRANTS

               (a)    The persons eligible to receive option grants under the 
Plan are as follows:

                           (i)     key employees (including officers and 
        directors) of the Corporation (or its parent or subsidiary corporations)
        who render services which contribute to the success and growth of the
        Corporation (or its parent or subsidiary corporations) or which may
        reasonably be anticipated to contribute to the future success and growth
        of the Corporation (or its parent or subsidiary corporations);

                          (ii)     the non-employee members of the Board or the
        non-employee members of the board of directors of any parent or
        subsidiary corporations; and

                         (iii)     those independent consultants or other 
        advisors who provide valuable services to the Corporation (or its parent
        or subsidiary corporations).

               (b)    The Plan Administrator shall have full authority to 
determine which eligible individuals are to receive option grants under the
Plan, the number of shares to be covered by each such grant, whether the granted
option is to be an incentive stock option ("Incentive Option") which satisfies
the requirements of Section 422 of the Internal Revenue Code or a non-statutory
option not intended to meet such requirements, the time or times at which each
such option is to become exercisable, and the maximum term for which the option
is to be outstanding.


                                       2.

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      IV.      STOCK SUBJECT TO THE PLAN

               (a) The stock issuable under the Plan shall be shares of the
Corporation's authorized but unissued or reacquired Common Stock. The maximum
number of shares which may be issued under the Plan shall not exceed 5,480,000
shares.* The total number of shares issuable under the Plan shall be subject to
adjustment from time to time in accordance with Section IV(d) of the Plan.

               (b) In no event may the aggregate number of shares of Common
Stock for which any one individual participating in the Plan may be granted
stock options and separately exercisable stock appreciation rights exceed
1,250,000 shares in the aggregate over the remaining term of the Plan, subject
to adjustment from time to time in accordance with Section IV(d) of the Plan.
For purposes of such limitation, no stock options or stock appreciation rights
granted prior to January 1, 1994 shall be taken into account.

               (c) Should an option expire or terminate for any reason prior to
exercise in full (including options cancelled in accordance with the
cancellation-regrant provisions of Section VIII of the Plan), the shares subject
to the portion of the option not so exercised shall be available for subsequent
option grants under the Plan. Unvested shares issued under the Plan and
subsequently repurchased by the Corporation, at the option exercise price paid
per share, pursuant to the Corporation's repurchase rights under the Plan, shall
be added back to the number of shares of Common Stock reserved for issuance
under the Plan and shall accordingly be available for reissuance through one or
more subsequent option grants under the Plan. Shares subject to any option
cancelled in accordance with Section IX of the Plan shall reduce on a
share-for-share basis the number of shares of Common Stock available for
subsequent option grants under this Plan. In addition, should the exercise price
of an outstanding option under the Plan be paid with shares of Common Stock,
then the number of shares of Common Stock available for issuance under the Plan

- -----------------------
* Adjusted to reflect (i) the 1 for 2.5 reverse Common Stock split effected by
the Company on August 18, 1991, (ii) the 670,000 share increase authorized by
the Board on March 18, 1992 and approved by the stockholders at the 1992 Annual
Meeting, (iii) the 700,000 share increase authorized by the Board on January 13,
1993 and approved by the stockholders at the 1993 Annual Meeting, (iv) the
650,000 share increase authorized by the Board on February 28, 1994 and approved
by the stockholders at the 1994 Annual Meeting, (v) the 500,000 share increase
authorized by the Board on January 25, 1995, and approved by the stockholders at
the 1995 Annual Meeting, (vi) the 1,200,000 share increase authorized by the
Board on January 24, 1996, and approved by the stockholders at the 1996 Annual
Meeting, and (vii) the 800,000 share increase authorized by the Board on
February 24, 1997 and approved by the stockholders at the 1997 Annual Meeting.
In no event, however, shall more than 4,793,277 shares of Common Stock be issued
under the Plan after February 28, 1997, subject to adjustment under Section
IV(d) in the event of changes in the Company's capital structure.

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shall be reduced by the gross number of shares for which the option is
exercised, and not by the net number of shares of Common Stock actually issued
to the option holder.

               (d) In the event any change is made to the Common Stock issuable
under the Plan by reason of any stock split, stock dividend, combination of
shares, exchange of shares or other change affecting the outstanding Common
Stock as a class without the Corporation's receipt of consideration, then
appropriate adjustments shall be made to (I) the maximum number and/or class of
securities issuable under the Plan, (II) the maximum number and/or class of
securities for which stock options and separately exercisable stock appreciation
rights may be granted to any one participant in the aggregate after December 31,
1993 and (III) the number and/or class of securities and exercise price per
share in effect under each outstanding option in order to prevent the dilution
or enlargement of benefits thereunder. The adjustments determined by the Plan
Administrator shall be final, binding and conclusive.

       V.      TERMS AND CONDITIONS OF OPTIONS

               Options granted pursuant to the Plan shall be authorized by
action of the Plan Administrator and may, at the Plan Administrator's
discretion, be either Incentive Options or non-statutory options. Individuals
who are not Employees (as defined in Section V.3.D below) may only be granted
non-statutory options. Each granted option shall be evidenced by one or more
instruments in the form approved by the Plan Administrator; provided, however,
that each such instrument shall comply with the terms and conditions specified
below. Each instrument evidencing an Incentive Option shall, in addition, be
subject to the applicable provisions of Section VI.

               1.     Option Price.

                      A.     The option price per share shall be fixed by the 
Plan Administrator, but in no event shall the option price per share be less
than eighty-five percent (85%) of the fair market value of a share of Common
Stock on the date of the option grant.

                      B.     The option price shall become immediately due upon 
exercise of the option and shall, subject to the provisions of Section X and the
instrument evidencing the grant, be payable in one of the alternative forms
specified below:

                           (i)      full payment in cash or check payable to the
        Corporation; or

                          (ii)      full payment in shares of Common Stock held 
        by the optionee for the requisite period necessary to avoid a charge to
        the Corporation's reported earnings and valued at fair market value on
        the Exercise Date (as such term is defined below); or

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                         (iii)      full payment through a combination of shares
        of Common Stock held by the optionee for the requisite period necessary
        to avoid a charge to the Corporation's reported earnings and valued at
        fair market value on the Exercise Date and cash or check payable to the
        Corporation; or

                          (iv)      full payment effected through a broker-
        dealer sale and remittance procedure pursuant to which the optionee
        shall provide irrevocable written instructions (I) to a
        Corporation-designated brokerage firm to (A) effect the immediate sale
        of a sufficient number of the purchased shares to enable such firm to
        remit to the Corporation, out of the sale proceeds available on the
        settlement date, sufficient funds to cover the aggregate option price
        payable for the purchased shares plus all applicable Federal and State
        income and employment taxes required to be withheld by the Corporation
        in connection with such purchase and (B) remit those funds to the
        Corporation on the settlement date, and (II) to the Corporation to
        deliver the certificates for the purchased shares directly to such
        brokerage firm.

                      For purposes of this subparagraph B, the Exercise Date 
shall be the date on which written notice of the option exercise is received by
the Corporation. Except to the extent the sale and remittance procedure is
utilized in connection with the exercise of the option, payment of the option
price for the purchased shares must accompany such notice.

                      C.     The fair market value per share of Common Stock on 
any relevant date under subparagraph A or B (and for all other valuation
purposes under the Plan) shall be determined in accordance with the following
provisions:

                           (i)      If the Common Stock is not at the time 
        listed or admitted to trading on any national stock exchange but is
        traded on the Nasdaq National Market, the fair market value shall be the
        closing selling price per share of Common Stock on the date in question,
        as reported by the National Association of Securities Dealers on the
        Nasdaq National Market or any successor system. If there is no reported
        closing selling price for the Common Stock on the date in question, then
        the closing selling price on the last preceding date for which such
        quotation exists shall be determinative of fair market value.

                          (ii)      If the Common Stock is at the time listed or
        admitted to trading on any national stock exchange, then the fair market
        value shall be the closing selling price per share of Common Stock on
        the date in question on the stock exchange determined by the Plan
        Administrator to be the primary market for the Common Stock, as such
        price is officially quoted

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        in the composite tape of transactions on such exchange. If there is no
        reported sale of Common Stock on such exchange on the date in question,
        then the fair market value shall be the closing selling price on the
        exchange on the last preceding date for which such quotation exists.

               2.     Term and Exercise of Options. Each option granted under 
the Plan shall be exercisable at such time or times, during such period, and for
such number of shares as shall be determined by the Plan Administrator and set
forth in the instrument evidencing such option; provided, however, that no such
option shall have a term in excess of ten (10) years from the grant date.

               3.     Limited Transferability of Options. During the lifetime of
the optionee, Incentive Options shall be exercisable only by the optionee and
shall not be assignable or transferable other than by will or by the laws of
descent and distribution following the optionee's death. However, non-statutory
options may, in connection with the optionee's estate plan, be assigned in whole
or in part during the optionee's lifetime to one or more members of the
optionee's immediate family or to a trust established exclusively for one or
more such family members. The assigned portion may only be exercised by the
person or persons who acquire a proprietary interest in the option pursuant to
the assignment. The terms applicable to the assigned portion shall be the same
as those in effect for the option immediately prior to such assignment and shall
be set forth in such documents issued to the assignee as the Plan Administrator
may deem appropriate.

               4.     Effect of Termination of Service.

                      A.     Should an optionee cease to remain in Service (as 
defined in subparagraph D below) for any reason (including death or permanent
disability as defined in Section 22(e)(3) of the Internal Revenue Code) while
the holder of one or more outstanding options granted to such optionee under the
Plan, then such option or options shall not (except to the extent otherwise
provided pursuant to Section XI below) remain exercisable for more than a
thirty-six (36)-month period (or such shorter period determined by the Plan
Administrator and specified in the instrument evidencing the grant) following
the date of such cessation of Service. Under no circumstances, however, shall
any such option be exercisable after the specified expiration date of the option
term. Each such option shall, during such thirty-six (36)-month or shorter
period, be exercisable only to the extent of the number of shares (if any) for
which the option is exercisable on the date of the optionee's cessation of
Service. Upon the expiration of such thirty-six (36)-month or shorter period or
(if earlier) upon the expiration of the option term, the option shall terminate
and cease to be exercisable. However, the option shall, immediately upon the
optionee's cessation of Service for any reason, terminate and cease to be
outstanding for any option shares for which the option is not otherwise at that
time exercisable.


                                       6.



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                      B.     Any outstanding option held by the optionee and 
exercisable in whole or in part on the date of his or her death may be
subsequently exercised, but only to the extent of the number of shares (if any)
for which the option is exercisable on the date of the optionee's cessation of
Service (less any option shares subsequently purchased by the optionee prior to
death), by the personal representative of the optionee's estate or by the person
or persons to whom the option is transferred pursuant to the optionee's will or
in accordance with the laws of descent and distribution. The right to exercise
the option for those shares shall terminate upon the earlier of (i) the third
anniversary of the date of the optionee's cessation of Service or (ii) the
specified expiration date of the option term.

                      C.     Notwithstanding subparagraphs A and B above, the 
Plan Administrator shall have complete discretion, exercisable either at the
time the option is granted or at any time while the option remains outstanding,
to permit one or more options held by the optionee under the Plan to be
exercised, during the limited period of exercisability provided under Section
V.4.A above, not only with respect to the number of shares for which each such
option is exercisable at the time of the optionee's cessation of Service but
also with respect to one or more subsequent installments for which the option
would otherwise have become exercisable had such cessation of Service not
occurred.

                      D.     For purposes of the foregoing provisions of this 
Section V.4 (and all other provisions of the Plan), the optionee shall be deemed
to remain in the SERVICE of the Corporation for so long as such individual
renders services on a periodic basis to the Corporation or any parent or
subsidiary corporation in the capacity of an Employee, a non-employee member of
the board of directors or an independent consultant or advisor, unless the
option agreement evidencing the option grant and/or the purchase agreement
evidencing the purchased option shares specifically provides otherwise. The
optionee shall be considered to be an EMPLOYEE for so long as such individual
remains in the employ of the Corporation or one or more of its parent or
subsidiary corporations, subject to the control and direction of the employer
entity as to the work to be performed and as to the manner and method of
performance.

               5.     Stockholder Rights.  An optionee shall have none of the 
rights of a stockholder with respect to any shares covered by the option until
such individual shall have exercised the option and paid the option price for
the purchased shares.

               6.     Repurchase Rights.  Unvested shares of Common Stock may be
issued under the Plan which are subject to repurchase by the Corporation in
accordance with the following provisions:

                      (a)     Upon the optionee's cessation of Service while 
        holding unvested shares under the Plan, the Corporation shall have the
        right to repurchase any or all of those unvested shares at the option
        price paid per share. The terms and conditions upon which such
        repurchase right shall be

                                       7.

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        exercisable (including the period and procedure for exercise and the
        appropriate vesting schedule for the purchased shares) shall be
        established by the Plan Administrator and set forth in the instrument
        evidencing such repurchase right.

                      (b)     All of the Corporation's outstanding repurchase 
        rights shall automatically terminate, and all shares subject to such
        terminated rights shall immediately vest in full, upon the occurrence of
        any Corporate Transaction under Section VII of this Plan, except to the
        extent: (i) any such repurchase right is to be assigned to the successor
        corporation (or parent thereof) in connection with the Corporate
        Transaction or (ii) such accelerated vesting is precluded by other
        limitations imposed by the Plan Administrator at the time the repurchase
        right is issued.

                      (c)     The Plan Administrator shall have the 
        discretionary authority, exercisable either before or after the
        optionee's cessation of Service, to cancel the Corporation's outstanding
        repurchase rights with respect to any or all unvested shares purchased
        or purchasable by the optionee under the Plan and thereby accelerate the
        vesting of those shares in whole or in part at any time.

      VI.      INCENTIVE OPTIONS.

               The terms and conditions specified below shall be applicable to
all Incentive Options granted under the Plan. Incentive Options may only be
granted to individuals who are Employees. Options which are specifically
designated as "non-statutory" options when issued under the Plan shall not be
subject to such terms and conditions.

               (a)    Option Price. The option price per share of the Common 
Stock subject to an Incentive Option shall in no event be less than one hundred
percent (100%) of the fair market value of a share of Common Stock on the date
of grant.

               (b)    Dollar Limitation. The aggregate fair market value
(determined as of the respective date or dates of grant) of the Common Stock for
which one or more options granted to any Employee after December 31, 1986 under
this Plan (or any other option plan of the Corporation or its parent or
subsidiary corporations) may for the first time become exercisable as incentive
stock options under the Federal tax laws during any one calendar year shall not
exceed the sum of One Hundred Thousand Dollars ($100,000). To the extent the
Employee holds two or more such options which become exercisable for the first
time in the same calendar year, the foregoing limitation on the exercisability
of such options as incentive stock options under the Federal tax laws shall be
applied on the basis of the order

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in which such options are granted. Should the number of shares of Common Stock
for which an Incentive Option first becomes exercisable in any calendar year
exceed the applicable One Hundred Thousand Dollar ($100,000) limitation, the
option may nevertheless be exercised for those excess shares in such calendar
year as a non-statutory option.

               (c)  10% Stockholder. If any individual to whom the Incentive
Option is granted is the owner of stock (as determined under Section 424(d) of
the Internal Revenue Code) possessing ten percent (10%) or more of the total
combined voting power of all classes of stock of the Corporation or any one of
its parent or subsidiary corporations, then the option price per share shall not
be less than one hundred and ten percent (110%) of the fair market value per
share of Common Stock on the grant date, and the option term shall not exceed
five (5) years, measured from such grant date.

               Except as modified by the preceding provisions of this Section
VI, all the provisions of the Plan shall be applicable to the Incentive Options
granted hereunder.

     VII.      CORPORATE TRANSACTION/CHANGE IN CONTROL

               (a)    In the event of any of the following transactions (a 
"Corporate Transaction"):

                           (i)      a merger or consolidation in which the
        Corporation is not the surviving entity, except for a transaction the 
        principal purpose of which is to change the State of the Corporation's
        incorporation,

                          (ii)      the sale, transfer or other disposition of 
        all or substantially all of the assets of the Corporation in liquidation
        or dissolution of the Corporation, or

                         (iii)      any reverse merger in which the Corporation 
        is the surviving entity but in which fifty percent (50%) or more of the
        Corporation's outstanding voting stock is transferred to persons
        different from those who held the stock immediately prior to such
        merger,

                      each outstanding option under the Plan shall automatically
accelerate so that each such option shall, immediately prior to the specified
effective date for the Corporate Transaction, become exercisable for the total
number of shares of Common Stock at the time subject to such option and may be
exercised for all or any portion of those shares as fully-vested shares of
Common Stock. However, an outstanding option under the Plan shall not so
accelerate if and to the extent: (i) such option is, in connection with the
Corporate Transaction, either to be assumed by the successor corporation or
parent thereof or be replaced with a comparable option to purchase shares of the
capital stock of the successor corporation or parent thereof or (ii) the
acceleration of such option is subject to

                                       9.



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other applicable limitations imposed by the Plan Administrator at the time of
grant. The determination of comparability under clause (i) above shall be made
by the Plan Administrator and its determination shall be final, binding and
conclusive.

               (b)    Each outstanding option under the Plan which is assumed in
connection with the Corporate Transaction or is otherwise to continue in effect
shall be appropriately adjusted, immediately after such Corporate Transaction,
to apply and pertain to the number and class of securities which would have been
issued, in consummation of such Corporate Transaction, to an actual holder of
the same number of shares of Common Stock as are subject to such option
immediately prior to such Corporate Transaction. Appropriate adjustments shall
also be made to the option price payable per share, provided the aggregate
option price payable for such securities shall remain the same. In addition, the
class and number of securities available for issuance under the Plan on both an
aggregate and per participant basis shall be appropriately adjusted to reflect
the effect of the Corporate Transaction upon the Corporation's capital
structure.

               (c)    In connection with any Change in Control (as defined 
below), the Plan Administrator shall have full power and authority, exercisable
either at the time the option is granted or at any time while the option remains
outstanding, to provide for the automatic acceleration of each outstanding
option under the Plan so that each such option shall, immediately prior to the
effective date of the Change in Control, become exercisable for the total number
of shares at the time subject to such option and may be exercised for all or any
portion of those shares as fully-vested shares of Common Stock. The Plan
Administrator shall also have full power and authority to condition such option
acceleration, and the termination of any of the Corporation's repurchase rights
with respect to any unvested shares purchased or purchasable under the Plan,
upon the subsequent termination of the optionee's Service within a designated
period following the Change in Control.

           A CHANGE IN CONTROL shall be deemed to occur in the event:

                           (i)     twenty-five percent (25%) or more of the
        Corporation's outstanding voting stock is acquired pursuant to a tender
        or exchange offer (A) which is made directly to the Corporation's
        stockholders by any person or related group of persons (other than the
        Corporation or a person that directly or indirectly controls, is
        controlled by or is under common control with, the Corporation) and (B)
        which the Board does not recommend the stockholders to accept; or

                          (ii)     there is a change in the composition of the 
        Board over a period of twenty-four (24) consecutive months or less such
        that a majority of the Board members ceases, by reason of one or more
        proxy contests for the election of Board members, to be comprised of
        individuals who either (A) have been Board members continuously since
        the beginning of such period or (B) have been elected or nominated for
        election as Board

                                       10.



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        members during such period by at least a majority of the Board members
        described in clause (A) who were still in office at the time such
        election or nomination was approved by the Board.

               (d)    Immediately following the consummation of a Corporate
Transaction, all outstanding options under the Plan shall terminate and cease to
be outstanding, except to the extent assumed by the successor corporation or its
parent company. Upon a Change in Control, each outstanding option accelerated
pursuant to subsection VII(c) above shall remain fully exercisable until the
expiration or sooner termination of the option term specified in the agreement
evidencing such grant.

               (e)    The exercisability as incentive stock options under the
Federal tax laws of any options accelerated in connection with a Corporate
Transaction or Change in Control shall remain subject to the dollar limitation
of Section VI(b) of the Plan. To the extent such dollar limitation is exceeded,
the accelerated option shall be exercisable as a non-statutory option under the
Federal tax laws.

               (f)    The grant of options under this Plan shall in no way 
affect the right of the Corporation to adjust, reclassify, reorganize or
otherwise change its capital or business structure or to merge, consolidate,
dissolve, liquidate or sell or transfer all or any part of its business or
assets.

    VIII.      CANCELLATION AND REGRANT OF OPTIONS

               The Plan Administrator shall have the authority to effect, at any
time and from time to time, with the consent of the affected optionees, the
cancellation of any or all outstanding options under the Plan and to grant in
substitution therefor new options under the Plan covering the same or different
numbers of shares of Common Stock but having an option price per share not less
than (i) eighty-five percent (85%) of the fair market value per share of the
Common Stock on the new grant date or (ii) one hundred percent (100%) of such
fair market value in the case of an Incentive Option or (iii) one hundred and
ten percent (110%) of such fair market value in the case of an Incentive Option
granted to a 10% Stockholder.

      IX.      STOCK APPRECIATION RIGHTS

               (a)    Provided and only if the Plan Administrator determines in 
its discretion to implement the stock appreciation right provisions of this
Section IX, one or more optionees may be granted the right, exercisable upon
such terms and conditions as the Plan Administrator may establish, to surrender
all or part of an unexercised option under the Plan in exchange for a
distribution from the Corporation in an amount equal to the excess of (i) the
fair market value (on the option surrender date) of the number of shares in
which

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the optionee is at the time vested under the surrendered option (or surrendered
portion thereof) over (ii) the aggregate option price payable for such vested
shares.

               (b)    No surrender of an option shall be effective hereunder 
unless it is approved by the Plan Administrator. If the surrender is so
approved, then the distribution to which the optionee shall accordingly become
entitled under this Section IX may be made in shares of Common Stock valued at
fair market value on the option surrender date, in cash, or partly in shares and
partly in cash, as the Plan Administrator shall in its sole discretion deem
appropriate.

               (c)    If the surrender of an option is rejected by the Plan
Administrator, then the optionee shall retain whatever rights the optionee had
under the surrendered option (or surrendered portion thereof) on the option
surrender date and may exercise such rights at any time prior to the later of
(i) five (5) business days after the receipt of the rejection notice or (ii) the
last day on which the option is otherwise exercisable in accordance with the
terms of the instrument evidencing such option, but in no event may such rights
be exercised more than ten (10) years after the date of the option grant.

               (d)    One or more officers of the Corporation subject to the
short-swing profit restrictions of the Federal securities laws may, in the Plan
Administrator's sole discretion, be granted limited stock appreciation rights in
tandem with their outstanding options under the Plan. Upon the occurrence of a
Hostile Take-Over, each outstanding option with such a limited stock
appreciation right shall automatically be cancelled, to the extent such option
is at the time exercisable for fully-vested shares of Common Stock (including
any shares which may vest in connection with such Hostile Take-Over). The
optionee shall in return be entitled to a cash distribution from the Corporation
in an amount equal to the excess of (i) the Take-Over Price of the vested shares
of Common Stock at the time subject to the cancelled option (or cancelled
portion of such option) over (ii) the aggregate exercise price payable for such
shares. The cash distribution payable upon such cancellation shall be made
within five (5) days following the consummation of the Hostile Take-Over. The
Plan Administrator shall pre-approve, at the time the limited stock appreciation
right is granted, the subsequent exercise of that right in accordance with the
terms of the grant and the provisions of this Section IX(d). No additional
approval of the Plan Administrator or the Board shall be required at the time of
the actual option cancellation and cash distribution. The balance of the option
(if any) shall continue to remain outstanding and exercisable in accordance with
the terms and conditions of the instrument evidencing such grant.

               (e)    For purposes of Section IX(d), the following definitions 
shall be in effect:

                      A HOSTILE TAKE-OVER shall be deemed to occur in the event
        any person or related group of persons (other than the Corporation or a
        person that directly or indirectly controls, is controlled by, or is
        under common

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        control with, the Corporation) directly or indirectly acquires
        beneficial ownership (within the meaning of Rule 13d-3 of the Securities
        Exchange Act of 1934) of securities possessing more than twenty-five
        percent (25%) of the total combined voting power of the Corporation's
        outstanding securities pursuant to a tender or exchange offer made
        directly to the Corporation's stockholders which the Board does not
        recommend such stockholders to accept.

                      The TAKE-OVER PRICE per share shall be deemed to be equal
        to the greater of (a) the fair market value per share on the date of
        cancellation, as determined pursuant to the valuation provisions of
        Section V.1.C, or (b) the highest reported price per share paid by the
        acquiring entity in effecting such Hostile Take-Over. However, to the
        extent the cancelled option is an Incentive Option, the Take-Over Price
        shall not exceed the clause (a) price per share.

               (f)    The shares of Common Stock subject to any option 
surrendered or cancelled for an appreciation distribution pursuant to this
Section IX shall NOT be available for subsequent option grant under the Plan.

       X.      LOANS OR INSTALLMENT PAYMENTS

               The Plan Administrator may, in its discretion, assist any
optionee (including any officer or director of the Corporation) in the exercise
of one or more options granted to such individual under the Plan, including the
satisfaction of any Federal and State income and employment tax obligations
arising therefrom, by (i) authorizing the extension of a loan from the
Corporation to such optionee or (ii) permitting the optionee to pay the option
price for the purchased Common Stock in installments over a period of years. The
terms of any such loan or installment method of payment (including the interest
rate and terms of repayment) will be upon such terms as the Plan Administrator
specifies in the applicable option agreement or otherwise deems appropriate
under the circumstances. Loans or installment payments may be granted with or
without security or collateral (other than to individuals who are independent
consultants or advisors, in which event the loan must be adequately secured by
collateral other than the purchased shares). However, the maximum credit
available to the optionee may not exceed the option price of the acquired shares
plus any Federal and State income and employment tax liability incurred by the
optionee in connection with the exercise of the option.

      XI.      EXTENSION OF EXERCISE PERIOD

               The Plan Administrator shall have full power and authority, to
extend the period of time for which the option is to remain exercisable
following the optionee's

                                       13.



   14


cessation of Service from the thirty-six (36) month or shorter period set forth
in the option agreement to such greater period of time as the Plan Administrator
shall deem appropriate. In no event, however, shall such option be exercisable
after the specified expiration date of the option term.

     XII.      AMENDMENT OF THE PLAN

               The Board shall have complete and exclusive power and authority
to amend or modify the Plan in any or all respects whatsoever; provided,
however, that no such amendment or modification shall, without the consent of
the holders, adversely affect rights and obligations with respect to options at
the time outstanding under the Plan. In addition, certain amendments may require
stockholder approval pursuant to applicable laws or regulations.


    XIII.      EFFECTIVE DATE AND TERM OF PLAN

               (a) The Plan was initially adopted by the Board on July 19, 1988
and approved by the Corporation's stockholders on March 29, 1989. The Plan was
subsequently amended by the Board on July 18, 1990, and such amendment was
approved by the Corporation's stockholders in October, 1990. In January 1991,
the Plan was again amended to increase by 480,000 shares the number of shares of
Common Stock issuable under the Plan, and such share increase was approved by
the Corporation's stockholders on March 20, 1991. The Board further amended the
Plan on May 22, 1991, with such amendments to become effective as of the date
the Corporation's Common Stock first became traded on the Nasdaq National
Market, in order to revise certain provisions previously required when the Plan
was subject to the permit requirements of the California Corporations
Department. On March 18, 1992, the Plan was amended and restated in its
entirety, including an increase of 670,000 shares to the number of shares of
Common Stock issuable thereunder. The 1992 restatement, including the
670,000-share increase, was approved by the stockholders at the 1992 Annual
Meeting. On January 13, 1993, the Board amended the Plan to increase by an
additional 700,000 shares the number of shares of Common Stock issuable under
the Plan, and such share increase was approved by the stockholders at the 1993
Annual Meeting. On February 28, 1994, the Board amended the Plan to increase by
an additional 650,000 shares the number of shares of Common Stock issuable under
the Plan, and such increase was approved by the stockholders at the 1994 Annual
Meeting. On January 25, 1995, the Board amended the Plan to increase by an
additional 500,000 shares the number of shares of Common Stock issuable under
the Plan, and such increase was approved by the stockholders at the 1995 Annual
Meeting. On January 24, 1996, the Board adopted an amendment which increased the
number of shares of Common Stock issuable under the Plan by an additional
1,200,000 shares, and such increase was approved by the stockholders at the 1996
Annual Meeting.


                                       14.



   15



               On February 24, 1997, the Board adopted a series of amendments to
the Plan (the "1997 Amendments") which (i) increased the number of shares of
Common Stock reserved for issuance over the term of the Plan by an additional
800,000 shares, (ii) rendered non-employee Board members serving as Plan
Administrator eligible to receive option grants under the Plan, (iii) allowed
unvested shares issued under the Plan and subsequently repurchased by the
Corporation at the option exercise price paid per share to be reissued under the
Plan, (iv) removed certain restrictions on the eligibility of non-employee Board
members to serve as Plan Administrator, (v) extended the term of the Option Plan
from July 19, 1998 to December 31, 2002 and (vi) effected a series of additional
changes to the provisions of the Plan (including the stockholder approval
requirements, the transferability of non-statutory stock options and the
elimination of the six (6)-month holding period requirement as a condition to
the exercise of stock appreciation rights) in order to take advantage of the
recent amendments to Rule 16b-3 of the 1934 Act which exempts certain officer
and director transactions under the Plan from the short-swing liability
provisions of the federal securities laws. The 1997 Amendments were approved by
the Corporation's stockholders at the 1997 Annual Meeting.

               (b) The provisions of the 1992 restatement and of each subsequent
amendment to the Plan shall apply only to stock options and stock appreciation
rights granted under the Plan from and after the applicable effective date of
such restatement or amendment. All stock options and stock appreciation rights
issued and outstanding under the Plan immediately prior to each such effective
date shall continue to be governed by the terms and conditions of the Plan (and
the respective agreements evidencing each such option or stock appreciation
right) as in effect on the date each such option or stock appreciation right was
previously granted, and nothing in the 1992 restatement or in any subsequent
amendment shall be deemed to affect or otherwise modify the rights or
obligations of the holders of such prior options or stock appreciation rights
with respect to their acquisition of shares of Common Stock under such options
or their exercise of such stock appreciation rights. However, the Plan
Administrator may, in its discretion, modify stock option or stock appreciation
right issued and outstanding immediately prior to the effective date of the 1992
restatement or any subsequent amendment to include one or more provisions to the
Plan added by such restatement or amendment.

               (c) Unless sooner terminated in accordance with Section VII, the
Plan shall terminate upon the earlier of (i) December 31, 2002 or (ii) the date
on which all shares available for issuance under the Plan shall have been issued
or cancelled pursuant to the exercise, surrender of cash-out of the stock
options and stock appreciation rights granted hereunder. If the date of
termination is determined under clause (i) above, then each stock option or
stock appreciation right outstanding on such date shall thereafter continue to
have force and effect in accordance with the provisions of the instruments
evidencing such grant.

               (d) Options may be granted under this Plan to purchase shares of
Common Stock in excess of the number of shares then available for issuance under
the Plan, provided any excess shares actually issued under the Plan are held in
escrow until stockholder

                                       15.



   16


approval is obtained for a sufficient increase in the number of shares available
for issuance under the Plan. If such stockholder approval is not obtained within
twelve (12) months after the date the first such excess option grants are made,
then (I) any unexercised excess options shall terminate and cease to be
exercisable and (II) the Corporation shall promptly refund the purchase price
paid for any excess shares actually issued under the Plan and held in escrow,
together with interest (at the applicable Short Term Federal Rate) for the
period the shares were held in escrow.

     XIV.      USE OF PROCEEDS

               Any cash proceeds received by the Corporation from the sale of
shares pursuant to options granted under the Plan shall be used for general
corporate purposes.

      XV.      REGULATORY APPROVALS

               The implementation of the Plan, the granting of any stock option
or stock appreciation right hereunder, and the issuance of stock upon the
exercise of any such option or stock appreciation right shall be subject to the
procurement by the Corporation of all approvals and permits required by
regulatory authorities having jurisdiction over the Plan, the options and stock
appreciation rights granted under it and the stock issued pursuant to it.


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