<PAGE>


                                 CHIRON CORPORATION
                           NOTICE OF GRANT OF STOCK OPTION

Chiron Corporation
4560 Horton Street
Emeryville, CA  94608
ID:  94-2754624

< < First_Name > > < < Last_Name > >         Option Number:   < < Number > >
< < Address_Line_1 > >                       Plan:            < < Plan > >
< < City, > > < < State > > < < Zip_Code > > ID:              < < SSN > >

You have been granted a(n) < < Long_Type > > to buy < < Shares_Granted > >
shares of Chiron Corporation stock at < < Option_Price > > per share,
effective as of  < < Option_Date > > (the "Option Grant Date").
     Your shares become exercisable as follows:
          < < Shares_Period_1 > > shares vest on  < < Vest_Date_Period_1 > >
          < < Shares_Period_2 > > shares will vest monthly thereafter with full
          vest on < < Vest_Date_Period_2 > >

     This Option will expire ten years from the Option Grant Date above.

     This Option shall become exercisable in accordance with the above-described
schedule.  In no event shall the Option become exercisable for any additional
Option Shares after Optionee's cessation of employment.  In no event may this
Option be exercised for any fractional shares.

     Optionee understands and agrees that the Option is granted subject to and
in accordance with the terms of the Chiron Corporation 1991 Stock Option Plan as
amended (the "Plan").  Optionee further agrees to be bound by the terms of the
Plan and the terms of the Option as set forth in the 1997-1 Form Stock Option
Agreement attached hereto as Exhibit A.  A copy of the Plan is available upon
request made to the Corporate Secretary at the Corporation's principal offices.

     NO EMPLOYMENT CONTRACT.  Nothing in this Notice or in the attached 1997-1
Form Stock Option Agreement or in the Plan shall confer upon Optionee any right
to continue in the employ of the Corporation or any affiliate or constitute any
contract or agreement of employment or interfere in any way with the right of
the Corporation or an affiliate to reduce such Optionee's compensation or to
terminate Optionee's employment at any time, with or without cause; but nothing
contained in this Notice shall affect any contractual rights of Optionee
pursuant to a written employment agreement.

     WITHHOLDING. The Option holder agrees, as a condition to the exercise of
this Option, to make appropriate arrangements with the Committee, the
Corporation, or any subsidiary that employs the Option holder for the
satisfaction of any federal, state or local income and employment tax
withholding requirements applicable to the exercise of this Option or the sale
of shares acquired under this Option.

     DEFINITIONS.  All capitalized terms in this Notice shall have the meaning
assigned to them in this Notice or in the attached 1997-1 Form Stock Option
Agreement.

DATED: ____________, ____             CHIRON CORPORATION


                              By:
                                    -------------------------------------------
                              Title:    President and Chief Executive Officer
                                    -------------------------------------------

ATTACHMENT
EXHIBIT A: 1997-1 FORM STOCK OPTION AGREEMENT


<PAGE>

                                      EXHIBIT A

                                 CHIRON CORPORATION
                         1997-1 FORM STOCK OPTION AGREEMENT


A.   MANNER OF EXERCISING OPTION.

     1.   This Option is exercisable by delivering notice in such form and to
such person as the Corporation may designate. The exercise date will be the date
that this notice is delivered ("Exercise Date").

     2.   Upon exercise, the Optionee must deliver to the Corporation full
payment of the Exercise Price in one or more of the following forms: cash,
shares of Common Stock of the Corporation held by the Option holder for the
requisite period to avoid a charge to the Corporation's earnings and valued as
of the Exercise Date, or delivery in a manner approved by the Corporation of
irrevocable instructions to a broker to promptly deliver to the Corporation the
amount of sale or loan proceeds to pay the Exercise Price.

     3.   In order to assist the Optionee in the acquisition of shares of Common
Stock pursuant to this Agreement, the Committee may (but is not required to)
authorize, under such terms and conditions as it may determine, the extension of
a loan to Optionee from the Corporation, the payment by Optionee of the Exercise
Price in installments, or a guarantee by the Corporation of a loan obtained by
Optionee from a third party.

     4.   The Option holder will furnish to the Corporation such documentation
as the Corporation may request to verify that the Optionee has the right to
exercise this Option.

     5.   For purposes of this Option, the Fair Market Value of a share of
Common Stock on any relevant date will be determined in accordance with the
following provisions:

          a.   If the Common Stock is not at the time listed or admitted to
trading on any stock exchange, then the Fair Market Value will be the average
between the reported high price and the reported low price on the date in
question of one share of Common Stock in the over-the-counter market, as such
prices are reported by the National Association of Securities Dealers through
its NASDAQ system or any successor system.

          b.   If the Common Stock is at the time listed or admitted to trading
on any stock exchange, then the Fair Market Value will be the average between
the reported high price and the reported low price on the date in question of
one share of Common Stock on the stock exchange that is the primary market for
the stock, as such prices are officially quoted on such exchange.

          c.   If the Common Stock is at the time neither listed nor admitted to
trading on any stock exchange nor traded in the over-the-counter market (or, if
the Committee determines that neither subparagraph (i) nor subparagraph (ii)
above reflects Fair Market Value) then the Fair Market Value will be determined
by the Committee after taking into account such factors as the Committee deems
appropriate.

B.   TERMINATION.  This Option will cease to be exercisable and will expire
prior to the Expiration Date should one of the following provisions become
applicable.  For purposes of these provisions, the terms "employee" and
"employment" include service as an employee, an independent contractor or a
consultant.

          a.   Should Optionee cease to be an employee of the Corporation or its
subsidiaries (other than by reason of death, permanent disability or termination
for cause as specified below) at any time during the option term, then the
period for exercising this Option will be reduced to a three (3) month period
commencing with the date of such cessation of employee status, but in no event
will this Option be exercisable at any time after the Expiration Date.  During
such limited period of exercisability, this Option may not be exercised for more
than that number of Option Shares (if any) for which it is exercisable on the
date of Optionee's cessation of employment status.  Upon the expiration of such
limited period or (if earlier) upon the Expiration Date, this Option will
terminate and cease to be outstanding.

          b.   Should Optionee die while this Option is outstanding, the
executors or administrators of Optionee's estate or Optionee's heirs or legatees
(as the case may be) will have the right to exercise this Option, but only with
respect to that number of Option Shares (if any) for which the Option is
exercisable on the date of Optionee's death.  This right will lapse and this
Option will cease to be exercisable upon the earlier of (A) the expiration of
the twelve (12)-month period measured from the date of Optionee's death or (B)
the Expiration Date.

          c.   Should Optionee become permanently disabled and cease by reason
thereof to be an employee of the Corporation or its subsidiaries at any time
during the option term, then Optionee will have a period of twelve (12) months
(commencing with the date of such cessation of employee status) during which to
exercise this Option; provided, however, that in no event will this Option be
exercisable at any time after the Expiration Date.  During this limited period
of exercisability, the Option may not be exercised for more than that number of
Option Shares (if any) for which it is exercisable on the date of Optionee's
cessation of employment.  Optionee will be deemed to be permanently disabled if
Optionee is, by reason of any medically determinable physical or mental
impairment expected to result in death or to be of continuous duration of not
less than 12 months, unable to engage in any substantial gainful employment.
Upon expiration of the limited period of exercisability or (if earlier) on the
Expiration Date, this Option will terminate and cease to be outstanding.

          d.   If Optionee's employment is terminated for cause (including, but
not limited to, any act of dishonesty, willful misconduct, fraud or embezzlement
or any unauthorized disclosure of confidential information or trade secrets),
then this Option will terminate and cease to be outstanding on the date of such
termination of employment.

C.   CHANGE IN CONTROL.

     1.   In the event the Corporation or its stockholders enter into an
agreement to dispose of all or substantially all of the assets or outstanding
capital stock of the Corporation by means of sale, merger, reorganization or
liquidation then this Option, to the extent not previously exercised or
terminated, will become exercisable, immediately prior to the consummation of
such sale, merger, reorganization or liquidation with respect to the full number
of shares of

<PAGE>

Common Stock purchasable under such option.  However, no such acceleration of
the Exercise Date will occur if the terms of the agreement require, as a
prerequisite to consummation of any such sale, merger, reorganization or
liquidation, that each such outstanding option will be either assumed by the
successor corporation or the parent thereof or replaced with a comparable option
to purchase shares of capital stock of the successor corporation or parent
thereof.  The determination of such comparability will be made by the Committee,
and its determination will be final, binding and conclusive.  Upon consummation
of the sale, merger, reorganization or liquidation contemplated by the
agreement, this Option, whether or not accelerated, will terminate and cease to
be exercisable, unless assumed pursuant to a written agreement by the successor
corporation or parent thereof.

     2.   This Agreement shall not in any 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.

D.   ADJUSTMENT IN OPTION SHARES.  Should any change be made to the Common Stock
by reason of any stock split, stock dividend, recapitalization, combination of
shares, exchange of shares or other change affecting the outstanding Common
Stock as a class without the Corporation's receipt of consideration, appropriate
adjustments shall be made to (i) the total number and/or class of securities
subject to this Option and (ii) the Exercise Price in order to reflect such
change and thereby preclude a dilution or enlargement of benefits hereunder.

E.   STOCKHOLDER RIGHTS.  The holder of this Option shall not have any
stockholder rights with respect to the Option Shares until such person shall
have exercised the option, paid the Exercise Price and become a holder of record
of the purchased shares.

F.   NONTRANSFERABILITY.  This Option shall be neither transferable nor
assignable by Optionee other than by will or by the laws of descent and
distribution following Optionee's death and may be exercised, during Optionee's
lifetime, only by Optionee.  The terms of this Option are binding upon the
executors, administrators, successors and assigns of the Optionee.

G.   COMPLIANCE WITH LAWS AND REGULATIONS.

     1.   The exercise of this Option and the issuance of the Option Shares upon
such exercise shall be subject to compliance by the Corporation and Optionee
with all applicable requirements of law relating thereto and with all applicable
regulations of any stock exchange on which the Common Stock may be listed for
trading at the time of such exercise and issuance.

     2.   The inability of the Corporation to obtain approval from any
regulatory body having authority deemed by the Corporation to be necessary to
the lawful issuance and sale of any Common Stock pursuant to this Option shall
relieve the Corporation of any liability with respect to the non-issuance or
sale of the Common Stock as to which such approval shall not have been obtained.

H.   NOTICES.  Any notice required to be given or delivered to the Corporation
under the terms of this Agreement shall be in writing and addressed to the
Corporation at its principal corporate offices.  Any notice required to be given
or delivered to Optionee shall be in writing and addressed to Optionee at the
address indicated below Optionee's signature line on the Grant Notice.  All
notices shall be deemed effective upon personal delivery or upon deposit in the
U.S. mail, postage prepaid and properly addressed to the party to be notified.

I.   EXCESS SHARES.  If the Option Shares covered by this Agreement exceed, as
of the Grant Date, the number of shares of Common Stock which may without
stockholder approval be issued under the Plan, then this Option shall be void
with respect to those excess shares, unless stockholder approval of an amendment
sufficiently increasing the number of shares of Common Stock issuable under the
Plan is obtained in accordance with the provisions of the Plan.

J.   ADDITIONAL TERMS APPLICABLE TO AN INCENTIVE OPTION.  In the event this
Option is designated an Incentive Option in the Grant Notice, the following
terms and conditions shall also apply to the grant:

          a.   This Option shall cease to qualify for favorable tax treatment as
an Incentive Option if (and to the extent) this Option is exercised for one or
more Option Shares: (A) more than three (3) months after the date Optionee
ceases to be an employee for any reason other than death or permanent disability
or (B) more than twelve (12) months after the date Optionee ceases to be an
employee by reason of death or permanent disability.

          b.   No installment under this Option shall qualify for favorable tax
treatment as an Incentive Option if (and to the extent) the aggregate Fair
Market Value (determined at the Grant Date) of the Common Stock for which such
installment first becomes exercisable hereunder would, when added to the
aggregate value (determined as of the respective date or dates of grant) of the
Common Stock or other securities for which this Option or any other Incentive
Options granted to Optionee prior to the Grant Date (whether under the Plan or
any other option plan of the Corporation or any parent or subsidiary) first
become exercisable during the same calendar year, exceed One Hundred Thousand
Dollars ($100,000) in the aggregate.  Should such One Hundred Thousand Dollar
($100,000) limitation be exceeded in any calendar year, this Option shall
nevertheless become exercisable for the excess shares in such calendar year as a
Non-Statutory Option.

          c.   Should the exercisability of this Option be accelerated upon a
Change in Control, then this Option shall qualify for favorable tax treatment as
an Incentive Option only to the extent the aggregate Fair Market Value
(determined at the Grant Date) of the Common Stock for which this Option first
becomes exercisable in the calendar year in which the Change in Control occurs
does not, when added to the aggregate value (determined as of the respective
date or dates of grant) of the Common Stock or other securities for which this
Option or one or more other Incentive Options granted to Optionee prior to the
Grant Date (whether under the Plan or any other option plan of the Corporation
or any parent or subsidiary) first become exercisable during the same calendar
year, exceed One Hundred Thousand Dollars ($100,000) in the aggregate.  Should
the applicable One Hundred Thousand Dollar ($100,000) limitation be exceeded in
the calendar year of such Change in Control, the Option may nevertheless be
exercised for the excess shares in such calendar year as a Non-Statutory Option.

          d.   Should Optionee hold, in addition to this Option, one or more
other options to purchase Common Stock which become exercisable for the first
time in the same calendar year as this Option, then the foregoing limitations on
the exercisability of such options as Incentive Options shall be applied on the
basis of the order in which such options are granted.