QuickLinks -- Click here to rapidly navigate through this document

Exhibit 10.502

CHIRON CORPORATION
NOTICE OF GRANT OF STOCK OPTION

«First_Name»   »Last_Name»   Chiron Corporation «Extra_Field_4»       4560
Horton Street         Emeryville, CA 94608 Option Number:   «Number»   ID:
94-275624 Plan:   «Plan»     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. The Option may become exercisable prior to completion
of the above-described schedule pursuant to the terms of Paragraph C of the
2001-1 Form Stock Option Agreement (the "Agreement") attached hereto as
Exhibit A, relating to certain terminations of employment following certain
corporate transactions. However, the Option shall not become exercisable for any
additional Option Shares after Optionee's cessation of employment, except to
that limited extent permitted under the terms of Paragraph B of the Agreement,
relating to termination by reason of death or Retirement. 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 Agreement. If you
misplaced your copy of the Prospectus or otherwise wish a new copy, you should
go to the Human Resources Stock page on Chiron's intranet site to view the
prospectus or contact the Corporate Secretary at the Corporation's principal
offices at 4560 Horton Street, Emeryville, CA 94608, Attention Stock Plan
Administration.

        No Employment Contract.    Nothing in this Notice or in the 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 Agreement.

DATED:                    , 2002   CHIRON CORPORATION
 
 
By:
 

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

 
 
Title:
 
Chairman and Chief Executive Officer

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

ATTACHMENT
Exhibit A: 2001 -1 Form Stock Option Agreement

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

EXHIBIT A
CHIRON CORPORATION
2001-1 FORM STOCK OPTION AGREEMENT

A.    Manner Of Exercising Option.

        1.    To the extent exercisable under the Grant Notice and this
Agreement, this Option may be exercised before the Expiration Date set forth in
the Grant Notice (or earlier termination of this Option) by delivering written
notice in such form and to such person as the Corporation specifies. The
exercise date will be the date that this notice is delivered ("Exercise Date").
The Option holder must furnish such documentation as the Corporation may request
to verify that such person has the right to exercise this Option. The holder of
this Option will not have any stockholder rights with respect to the Option
Shares until such person has exercised the Option, paid the Exercise Price and
become a holder of record of the purchased shares.

        2.    Upon exercise, the Optionee must pay the full Exercise Price to
the Corporation 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. In order to assist in the acquisition of
shares of Common Stock pursuant to this Agreement, the Committee may (but is not
required to) authorize 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.

        3.    For purposes of this Option, Fair Market Value of a share of
Common Stock on any date will be determined under the terms of the Plan, which,
as long as the Common Stock is traded on the NASDAQ system and the Committee
administering the Plan does not determine otherwise, will be the average of the
high and low price of one share of Common Stock during NASDAQ's regular trading
session, as determined by the Committee using such publicly available sources as
it may specify.

B.    Termination.    If the Optionee's employment terminates before the
Expiration Date, this Option will expire early and cease to be exercisable in
accordance with the following provisions. For purposes of these provisions, the
term "employment" includes service as an employee, an independent contractor or
a consultant for the Corporation or a parent or subsidiary entity.

        1.    If Optionee terminates employment other than by reason of
Retirement, death, a disability that qualifies for benefits under the
Corporation's long-term disability program, or Cause (each as defined below)
during the option term, this Option will terminate on the earlier of the
Expiration Date or 3 months after the date of termination of employment. For
purposes of this paragraph B, an employee who goes on an approved disability
leave will be deemed to have terminated employment on the earlier of the end of
such leave (if Optionee has not returned to employment with the Corporation on
or before the end of such leave) or one year after the beginning of the leave.

        2.    If Optionee terminates employment by Retirement during the option
term, this Option will terminate on the earlier of the Expiration Date or
36 months after such termination of employment. Retirement means termination of
employment by an employee (by reason other than death or Cause) after all of the
following has occurred (i) the Optionee has completed 5 or more years of
continuous employment, (ii) the Optionee has attained age 55 and (iii) the sum
of the Optionee's age in full years and full years of employment equals at least
65.

        3.    If Optionee takes an approved disability leave during the option
term and qualifies for benefits under the Corporation's long-term disability
insurance program (but not for Retirement), the Option will terminate on the
earlier of the Expiration Date or 36 months after the start of the leave.

2

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

        4.    If Optionee is on an approved leave of absence without pay, each
Vesting Date (i.e., each date on which Optionee would otherwise become eligible
to exercise this Option for the initial or additional number of shares if he or
she is then still employed by the Corporation) shall be deferred by the number
of days of such unpaid leave (in excess of 31 in the case of a personal leave),
provided that in the case of a leave during which Optionee has a statutory or
contractual right to reemployment for some period, vesting shall be deferred by
the number of days by which such leave extends beyond the date of lapse of such
right.

        5.    If Optionee dies while this Option is outstanding, the person or
entity who succeeds to this Option will have the following period to exercise
this Option: (i) if Optionee is employed by the Corporation at the time of
death, the 36 month period following the date of death, (ii) if Optionee
terminated employment before death by reason other than Retirement, Cause or
disability that qualifies for benefits under the Corporation's long-term
disability program, the 12 month period following the date of death or (iii) if
Optionee terminated employment before death by reason of Retirement or
disability that qualifies for benefits under the Corporation's long term
disability program, 36 months after the date of such Retirement or, in the case
of a qualifying disability, the start of the disability leave. However, in no
event can this Option be exercised after the Expiration Date.

        6.    After Optionee's termination of employment, this Option cannot be
exercised for more than that number of Option Shares (if any) for which it is
exercisable on the date of such termination, provided that (i) this shall be
subject to paragraph C below and (ii) if termination occurs by reason of death
or Retirement (including termination by reason of disability after becoming
eligible for Retirement), then during the 36 month period of limited
exercisability following such termination of employment the Option will continue
to vest and become (and remain) exercisable as if the Optionee continued as an
employee during such period. Upon the expiration of any applicable limited
period of exercise or (if earlier) upon the Expiration Date, this Option will
terminate and cease to be outstanding.

        7.    Notwithstanding any provision of this Agreement to the contrary,
if Optionee's employment is terminated for Cause or if, during any limited
period of exercisability following termination of employment by reason of
Retirement or disability that qualifies for benefits under the Corporation's
long-term disability program, Optionee engages in any activity which would
justify termination for Cause, as defined in paragraph C below, then this Option
will terminate and cease to be outstanding on the date of such termination of
employment or, if such activity occurs after termination of employment, the date
the Optionee engages in such activity. If any provision of this paragraph
contravenes or is invalid under the applicable laws of any state, this entire
paragraph will not be invalidated, but will be construed and enforced insofar as
the laws of that state are concerned as not containing the particular provision
or provisions that is invalid in that state.

C.    Change In Control.

        1.    Failure to Assume. If the Corporation or its stockholders enter
into an agreement to dispose of all or substantially all of the assets of the
Corporation, enter into an agreement to merge or consolidate with another entity
or enter into a plan of reorganization or liquidation, then this Option, to the
extent not previously exercised or terminated, may be exercised, immediately
before the consummation of such transaction with respect to all the shares of
Common Stock purchasable under this Option, unless this Option will be either
continued or assumed by the successor entity or its parent or replaced with a
comparable option to purchase equity interests of the successor entity or parent
thereof. The Committee will determine such comparability, and its determination
will be final, binding and conclusive. Upon consummation of such a transaction,
this Option, whether or not accelerated, will terminate and cease to be
exercisable, unless continued or assumed by the successor entity or parent
thereof.

3

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

        2.    Certain Terminations Following a Change in Control. If there is a
Change in Control of the Corporation pursuant to which the exercisability of the
Option does not accelerate in full pursuant to 1. above and within twenty-four
(24) calendar months thereafter there is a Qualifying Termination of Optionee's
employment, then this Option will become immediately exercisable for all of the
Option Shares then subject to this Option. For this purpose, the following
definitions apply:

a.A "Change in Control" of the Corporation shall be deemed to have occurred as
of the first day that any one or more of the following conditions is satisfied
and regulatory approval has been granted if necessary:

i.The "beneficial ownership" (as defined in Rule 13d-3 under the Securities
Exchange Act of 1934) of securities representing more than thirty percent (30%)
of the combined voting power of all securities of the Corporation is acquired,
directly or indirectly, by a Person (other than the Corporation, any trustee or
other fiduciary holding securities under an employee benefit plan of the
Corporation or an affiliate thereof, or any corporation owned, directly or
indirectly, by the stockholders of the Corporation in substantially the same
proportions as their ownership of stock of the Corporation); or

ii.During any period of two (2) consecutive years, individuals who at the
beginning of such period constitute the Board of Directors of the Corporation
and any new director (other than a director designated by a person who has
entered into an agreement with the Corporation to effect a transaction described
in i. above) whose election by the Board of Directors or nomination for election
by the Corporation's stockholders was approved by a vote of at least two-thirds
of the directors then still in office who either were directors at the beginning
of the period or whose election or nomination for election was previously so
approved, cease for any reason to constitute a majority thereof; or

iii.The stockholders of the Corporation approve a definitive agreement to sell
or otherwise dispose of all or substantially all of its assets, or adopt a plan
for liquidation, provided that such sale or liquidation has not been abandoned.

Notwithstanding anything else contained herein to the contrary, in no event
shall a Change in Control be deemed to have occurred by reason of a purchase, or
series of purchases of Corporation stock by Novartis or its successor such that
the acquiring entity remains subject to the terms of that certain Governance
Agreement dated as of January 5, 1995, as amended through December 9, 2000,
provided the acquiring entity's Corporation stock holdings, direct or indirect,
in the aggregate, represent less than seventy-nine and nine-tenths of a percent
(79.9%) of the combined voting power of all outstanding Corporation securities.
In addition, in no event shall a Change in Control be deemed to have occurred,
with respect to the Optionee, if the Optionee is part of a purchasing group that
consummates the Change-in-Control transaction. The Optionee shall be deemed
"part of a purchasing group" for purposes of the preceding sentence if the
Optionee is an equity participant in the purchasing company or group (except
for: (i) passive ownership of less than three percent (3%) of the stock or other
equity of the purchasing company; or (ii) ownership of equity participation in
the purchasing company or group which is otherwise not significant, as
determined prior to the Change in Control by a majority of the nonemployee
continuing Directors).

b."Qualifying Termination" means an involuntary termination of the Optionee's
employment by the Corporation for reasons other than Cause, death or disability.

c."Cause" means:

i.The Optionee's willful failure to substantially perform his/her duties with
the Corporation (other than any such failure resulting from disability);

4

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

ii.The Optionee's material act of dishonesty, fraud or embezzlement against the
Corporation, unauthorized disclosure of confidential information or trade
secrets of any of the Corporation or an affiliate (whether or not in violation
of any confidentiality agreement) or other willful conduct (other than conduct
covered under (i) above) that is demonstrably injurious to the Corporation,
monetarily or otherwise; or

iii.The Optionee's having been convicted of a felony.

For purposes of this subparagraph, no act, or failure to act, on the Optionee's
part shall be deemed "willful" unless done, or omitted to be done, by the
Optionee not in good faith and without reasonable belief that the action or
omission was in the best interests of the Corporation.

        3.    Right to Effect Transactions. This Agreement does 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.    If there is a 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 will 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.    Limited Transferability.    This Option cannot be transferred or assigned
other than by will or by the laws of descent and distribution and, during
Optionee's lifetime, can only be exercised by Optionee, unless and to the extent
that this Option is originally designated a Non-Statutory Option, in which case,
subject to such limitations as the Corporation may establish from time to time
for administrative and regulatory compliance reasons (including continued
eligibility of Registration Form S-8), this Option may be assigned by Optionee
by gift or pursuant to a domestic relations order to one or more of Optionee's
family members or an entity owned, benefiting or controlled by the Optionee or
one or more of Optionee's family members. Notwithstanding the foregoing, the
Optionee may also designate a beneficiary to whom this Option will automatically
be transferred if still outstanding upon the Optionee's death. The terms of this
Option are binding upon the executors, administrators, successors and assigns of
the Optionee.

F.    Compliance With Plan, Laws And Regulations.    The exercise of this Option
and the issuance of the Option shares upon such exercise is subject to the terms
of the plan and compliance by the Corporation and Optionee with all applicable
laws and with all applicable regulations of any stock exchange on which the
common stock is listed for trading at the relevant time. If the Corporation
cannot obtain approval from any regulatory body having authority deemed by the
Corporation to be necessary to the lawful issuance of common stock pursuant to
this Option, the Corporation will not have any liability with respect to the
failure to issue the common stock as to which such approval is not obtained.

G.    Additional Terms Applicable To An Incentive Option.    If this Option is
designated an Incentive Option in the Grant Notice, the following terms and
conditions will also apply to the grant:

        1.    This Option will not qualify for favorable tax treatment as an
Incentive Option to the extent that it is exercised: (A) more than 3 months
after the date Optionee ceases to be an employee for any reason other than death
or permanent and total disability or (B) more than 12 months after the date
Optionee ceases to be an employee by reason of permanent and total disability.
For this purpose (i) permanent and total disability means the inability to
engage in any substantial gainful activity by reason of any medically
determinable physical or mental impairment which can be expected to result in
death or which has lasted or can be expected to last for a continuous period of
not less than 12 months and (ii) an employee on a leave of absence will be
deemed to have terminated employment on the 91st day after the employee no
longer has a contractual or statutory right to reemployment.

5

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

        2.    To the extent that the aggregate Fair Market Value of the stock
for which options intended to be Incentive Options first become exercisable
during any calendar year (under this Plan or any other plan of the Corporation
or any parent or subsidiary and whether by reason of initial installment
exercisability or acceleration of exercisability upon a Change in Control) would
exceed $100,000 in the aggregate, the options shall not qualify as Incentive
Options, but shall be exercisable as Non-Statutory Options. The foregoing limit
will be applied by taking into account options in the order in which they were
granted.

6

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

ADDENDUM
TO
STOCK OPTION AGREEMENT

        The following provisions are hereby incorporated into, and are hereby
made a part of, that certain Stock Option Agreement (the "Option Agreement") by
and between Chiron Corporation (the "Corporation")
and                        ("Optionee") evidencing the stock option (the
"Option") granted this day to Optionee under the terms of the Corporation's 1991
Stock Option Plan, and such provisions are effective immediately. All
capitalized terms in this Addendum, to the extent not otherwise defined herein,
shall have the meanings assigned to them in the Option Agreement.

INVOLUNTARY TERMINATION FOLLOWING
A CHANGE IN CONTROL

        For purposes of Section C. of the Option Agreement, relating to
involuntary termination of Service following a Change in Control, the following
additional provisions shall apply:

        1.    For purposes of determining whether the Corporation's termination
of Optionee's employment is for Cause, Optionee's willful failure to
substantially perform his/her duties with the Corporation shall not constitute
Cause unless both (i) such failure does not occur by reason of disability or
after the Optionee has notified the Corporation in writing of his or her
termination for Good Reason (as defined below), but in the latter case, only if
the Corporation has not requested a Transition Employment Period (as defined
below) for Optionee and (ii) a written demand for substantial performance is
delivered to the Optionee that specifically identifies the manner in which the
Corporation believes that the Optionee has willfully failed to substantially
perform his/her duties and the Optionee has failed to resume substantial
performance of his/her duties on a continuous basis within thirty (30) calendar
days of receiving such demand;

        2.    The Corporation will be deemed to have involuntarily terminated
Optionee's employment and a Qualified Termination shall be deemed to have
occurred if Optionee voluntarily terminates employment for Good Reason pursuant
to a written notice of termination delivered to the Corporation by the Optionee;
provided that, if upon receiving such notice of termination, the Corporation
requests that the Optionee remain an employee for a period ending no later than
six (6) months following the date of the Change in Control (the "Transition
Employment Period") with compensation and benefits equal to or greater than the
Optionee's compensation and benefits immediately before the Qualifying
Termination (or, if more favorable to the Optionee, immediately before the
Change in Control), the Optionee will not be deemed to have a Qualifying
Termination unless he or she remains employed throughout the Transition Period
or Executive's employment earlier terminates due to death, disability or
involuntary termination by the Corporation for reason other than Cause.

        3.    For purposes of this Addendum, "Good Reason" shall mean the
occurrence, without the Optionee's express written consent, of any one or more
of the following:

        a.    The assignment of the Optionee to duties materially inconsistent
with the Optionee's authorities, duties, responsibilities as an employee of the
Corporation, or a material reduction in the nature or status of the Optionee's
authorities, duties, or responsibilities than those in effect immediately
preceding the Change in Control;

        b.    The Corporation's requiring the Optionee to be based at a location
which is at least fifty (50) miles further from the Optionee's current primary
residence than is such residence from the Corporation's current headquarters,
except for required travel on the Corporation's business to an extent
substantially consistent with the Optionee's business obligations as of the
Effective Date;

7

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

        c.    A material reduction in the Optionee's Base Salary or bonus
opportunity as in effect on the Effective Date or as the same shall be increased
from time to time;

        d.    A material reduction in the Optionee's level of participation in
any of the Corporation's short- and/or long-term incentive compensation plans,
or employee benefit or retirement plans, policies, practices, or arrangements in
which the Optionee participates immediately preceding the Change in Control;
provided, however, that reductions in the levels of participation in any such
plans shall not be deemed to be "Good Reason" if the Optionee's reduced level of
participation in each such program remains substantially consistent with the
average level of participation of other employees who have positions
commensurate with the Optionee's position. Long-term incentive plans shall mean
the Chiron Executive Long-Term Incentive Plan, the 1991 Stock Option Plan, and
any other similar plans instituted by the Corporation.

However, the occurrence of an event set forth in (a) through (d) above shall not
constitute Good Reason if the Corporation has cured such event within fifteen
(15) days of receipt of written notice from the Optionee that such event has
occurred and constitutes Good Reason.

IN WITNESS WHEREOF, Chiron Corporation has caused this Addendum to be executed
by its duly authorized officer as of the Effective Date specified below.

    Very truly yours,
 
 
CHIRON CORPORATION
 
 
By:
 

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

 
 
Title:
 

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

EFFECTIVE DATE:

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

 

8

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

QuickLinks

CHIRON CORPORATION NOTICE OF GRANT OF STOCK OPTION
EXHIBIT A CHIRON CORPORATION 2001-1 FORM STOCK OPTION AGREEMENT
ADDENDUM TO STOCK OPTION AGREEMENT
INVOLUNTARY TERMINATION FOLLOWING A CHANGE IN CONTROL