CHIRON CORP
DEF 14A, 1996-04-11
IN VITRO & IN VIVO DIAGNOSTIC SUBSTANCES
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<PAGE>
                            SCHEDULE 14A INFORMATION
 
                  Proxy Statement Pursuant to Section 14(a) of
            the Securities Exchange Act of 1934 (Amendment No.    )
 
    Filed by the Registrant /X/
    Filed by a Party other than the Registrant / /
 
    Check the appropriate box:
    / /  Preliminary Proxy Statement
    / /  Confidential, for Use of the Commission Only (as permitted by Rule
         14a-6(e)(2))
    /X/  Definitive Proxy Statement
    / /  Definitive Additional Materials
    / /  Soliciting  Material  Pursuant  to  Section  240.14a-11(c)  or  Section
         240.14a-12
                                CHIRON CORPORATION
- --------------------------------------------------------------------------------
                (Name of Registrant as Specified In Its Charter)
 
- --------------------------------------------------------------------------------
    (Name of Person(s) Filing Proxy Statement, if other than the Registrant)
 
Payment of Filing Fee (Check the appropriate box):
 
/ /  $125 per  Exchange Act  Rules 0-11(c)(1)(ii),  14a-6(i)(1), 14a-6(i)(2)  or
     Item 22(a)(2) of Schedule 14A.
/ /  $500  per  each party  to  the controversy  pursuant  to Exchange  Act Rule
     14a-6(i)(3).
/ /  Fee  computed  on   table  below   per  Exchange   Act  Rules   14a-6(i)(4)
     and 0-11.
     1) Title of each class of securities to which transaction applies:
        ------------------------------------------------------------------------
     2) Aggregate number of securities to which transaction applies:
        ------------------------------------------------------------------------
     3) Per unit price or other underlying value of transaction computed
        pursuant to Exchange Act Rule 0-11 (Set forth the amount on which the
        filing fee is calculated and state how it was determined):
        ------------------------------------------------------------------------
     4) Proposed maximum aggregate value of transaction:
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     5) Total fee paid:
        ------------------------------------------------------------------------
/X/  Fee paid previously with preliminary materials.
/ /  Check box if any part of the fee is offset as provided by Exchange Act Rule
     0-11(a)(2)  and identify the  filing for which the  offsetting fee was paid
     previously. Identify the previous filing by registration statement  number,
     or the Form or Schedule and the date of its filing.
     1) Amount Previously Paid:
        ------------------------------------------------------------------------
     2) Form, Schedule or Registration Statement No.:
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     3) Filing Party:
        ------------------------------------------------------------------------
     4) Date Filed:
        ------------------------------------------------------------------------
<PAGE>
[LOGO]                                                            April 11, 1996
 
To the Stockholders of
CHIRON CORPORATION
 
    You  are cordially invited  to attend the Annual  Meeting of Stockholders of
Chiron Corporation on May  16, 1996, at  10:00 a.m., which will  be held in  the
auditorium  at  our  Emeryville  headquarters,  1450  53rd  Street,  Emeryville,
California 94608.
 
    The attached  Notice  of Annual  Meeting  and Proxy  Statement  explain  the
business to be conducted at the Annual Meeting.
 
    Also  included in  this package is  Chiron's 1995 Annual  Report. The Annual
Report is in  summary form, containing  selected financial data,  our letter  to
stockholders,  and highlights of operations. You will find the Company's audited
consolidated financial statements enclosed as a separate brochure in a pocket at
the back of the Annual Report.
 
    Whether or not you plan to attend the Annual Meeting, please sign, date, and
return the enclosed proxy  promptly in the accompanying  reply envelope. If  you
decide  to attend the Annual Meeting and wish to change your proxy vote, you may
do so by giving notice and voting in person at the Annual Meeting.
 
    We look forward to seeing you at the Annual Meeting.
 
                                          EDWARD E. PENHOET
 
                                          EDWARD E. PENHOET,
                                            PRESIDENT AND
                                            CHIEF EXECUTIVE OFFICER
<PAGE>
                               CHIRON CORPORATION
                               4560 HORTON STREET
                          EMERYVILLE, CALIFORNIA 94608
 
                    NOTICE OF ANNUAL MEETING OF STOCKHOLDERS
                          MAY 16, 1996, AT 10:00 A.M.
 
    You  are hereby notified  that the Annual Meeting  of Stockholders of Chiron
Corporation ("Chiron"  or the  "Company")  will be  held  at 1450  53rd  Street,
Emeryville,  California,  on Thursday,  May  16, 1996,  at  10:00 a.m.,  for the
following purposes:
 
        1.  To elect three Class III directors to hold office for three years;
 
        2.   To consider  and  vote upon  a proposal  to  approve and  adopt  an
    amendment to the Company's Restated Certificate of Incorporation to increase
    the  authorized number  of shares  of Common Stock  of the  Company from 100
    million to 500 million;
 
        3.   To consider  and vote  upon  a proposal  to approve  the  Company's
    amended  1991 Stock Option Plan to change the formula for granting automatic
    annual stock options to  non-employee directors, to add  an annual grant  of
    automatic  share rights for  non-employee directors, and  to add performance
    units, which are restricted shares, share rights and share units awarded  to
    corporate vice-presidents and other executive officers which comply with the
    requirements of Internal Revenue Code Section 162(m);
 
        4.   To  ratify the  selection of KPMG  Peat Marwick  LLP as independent
    public accountants for the current fiscal year; and
 
        5.  To transact  such other business that  may properly come before  the
    Annual Meeting or any adjournments or postponements thereof.
 
    Stockholders  of record at the  close of business on  March 29, 1996 will be
entitled to vote at the Annual Meeting.  A list of the stockholders entitled  to
vote  at the Annual Meeting will be  open to the examination of any stockholder,
for any purpose  germane to the  meeting, during ordinary  business hours for  a
period of ten days prior to the meeting at the principal executive office of the
Company at 4560 Horton Street, Emeryville, California 94608.
 
    WHETHER OR NOT YOU PLAN TO ATTEND THE ANNUAL MEETING, PLEASE SIGN, DATE, AND
RETURN  THE ENCLOSED PROXY IN THE REPLY  ENVELOPE PROVIDED. The prompt return of
your proxy will assist us in preparing for the Annual Meeting.
 
                                          BY ORDER OF THE BOARD OF DIRECTORS
 
                                          WILLIAM G. GREEN
                                          WILLIAM G. GREEN,
                                            SECRETARY
 
Emeryville, California
April 11, 1996
<PAGE>
                                PROXY STATEMENT
                                      FOR
                         ANNUAL MEETING OF STOCKHOLDERS
                            TO BE HELD MAY 16, 1996
 
    These  proxy materials are furnished in  connection with the solicitation of
proxies by the Board of Directors of CHIRON CORPORATION, a Delaware  corporation
("Chiron"  or the "Company"),  for the Annual Meeting  of Stockholders of Chiron
(the "Annual  Meeting"),  to  be  held  in  the  auditorium  at  our  Emeryville
headquarters,  1450 53rd Street,  Emeryville, California 94608  at 10:00 a.m. on
May 16, 1996, and  at any adjournments or  postponements of the Annual  Meeting.
These  proxy materials were first  mailed to stockholders on  or about April 11,
1996.
 
                               PURPOSE OF MEETING
 
    The specific proposals to be considered and acted upon at the Annual Meeting
are summarized in  the accompanying  Notice of Annual  Meeting of  Stockholders.
Each  of these proposals is  described in more detail  in subsequent sections of
this Proxy Statement.
 
                         VOTING RIGHTS AND SOLICITATION
 
    The Company has one type of security entitled to vote at the Annual Meeting,
its Common Stock (the "Common  Stock"). If you were  a stockholder of record  of
Common  Stock at the  close of business on  March 29, 1996, you  may vote at the
Annual Meeting. Each  share entitles  you to  one vote  on each  matter to  come
before  the Annual Meeting. On  March 29, 1996, there  were 42,182,298 shares of
Common Stock issued  and outstanding.  The Certificate of  Incorporation of  the
Company  does not provide  for cumulative voting.  If you were  a stockholder of
record of Cetus Corporation common stock at  the close of business on March  29,
1996,  and have not exchanged  your Cetus common stock  for Chiron Common Stock,
you nevertheless may  vote at  the Annual Meeting.  Each share  of Cetus  common
stock  entitles you to 0.3 of one vote  on each matter to come before the Annual
Meeting. If you were a  stockholder of record of  Viagene, Inc. common stock  at
the  close of business  on March 29,  1996, and have  not exchanged your Viagene
common stock for Chiron  Common Stock, you nevertheless  may vote at the  Annual
Meeting.  Each share of Viagene common stock entitles you to .095220 of one vote
on each matter to come before the Annual Meeting.
 
    If you are unable to attend the  Annual Meeting, you may vote by proxy.  The
enclosed proxy is solicited by the Chiron Board of Directors and, when the proxy
card  is returned  properly completed, it  will be  voted as you  direct on your
proxy card. You are urged to specify your choices on the enclosed proxy card. If
a proxy card is signed and returned without choices specified, in the absence of
contrary instructions, the shares of Common Stock represented by such proxy will
be voted "FOR" Proposals 1, 2, 3 and  4 and will be voted in the proxy  holders'
discretion as to other matters that may properly come before the Annual Meeting.
 
    You  may revoke or change  your proxy at any time  before it is exercised at
the Annual Meeting. To do this, send  a written notice of revocation or  another
signed  proxy with a later date than appears  on the proxy you wish to revoke to
the Secretary of Chiron, William G. Green, at the Company's principal  executive
office.  You also may revoke your proxy by giving notice and voting in person at
the Annual Meeting.
 
    The Company will  pay the cost  of soliciting these  proxies, including  the
printing,  handling, and  mailing of the  proxies and related  material, and the
actual  expenses  incurred  by  brokerage  houses,  custodians,  nominees,   and
fiduciaries  in forwarding proxy material to  the beneficial owners of stock. To
assure that holders of a majority of the  stock will be present in person or  by
proxy  at the Annual Meeting, certain officers, directors, and regular employees
of Chiron may solicit proxies by  telephone, telegraph, facsimile or in  person.
These persons will receive no extra compensation for their services.
 
                                       1
<PAGE>
                               VOTING PROCEDURES
 
    The  three nominees for election as directors  at the 1996 Annual Meeting of
Stockholders who receive the greatest number  of votes cast for the election  of
directors at that meeting by the holders of the Company's Common Stock, entitled
to  vote at that meeting, a quorum  being present, shall become directors at the
conclusion of the tabulation of votes.
 
    The affirmative vote of the majority of shares of Common Stock having voting
power present  in  person or  represented  by proxy  at  the Annual  Meeting  is
required  to adopt the proposals relating to approval of the amended Chiron 1991
Stock Option Plan  and the amendment  of the Company's  Restated Certificate  of
Incorporation.
 
    The  Inspector  of  Elections will  treat  an abstention  or  withholding of
authority to  vote on  the election  of directors  by a  stockholder present  in
person  or represented by proxy at the meeting as unvoted for such purposes. The
Inspector of Elections will treat an  abstention as to the proposal relating  to
approval  of the amended Chiron 1991 Stock  Option Plan or the proposal relating
to  approval  of  the  amendment  of  the  Company's  Restated  Certificate   of
Incorporation  by a stockholder present in person or represented by proxy at the
meeting as a vote "against" the  matter for such purposes. However, pursuant  to
Delaware  law  and the  Company's Bylaws,  broker non-votes  as to  the proposal
relating to  approval  of the  amended  Chiron 1991  Stock  Option Plan  or  the
proposal  relating  to  approval  of the  amendment  of  the  Company's Restated
Certificate of Incorporation are treated as shares of Common Stock not  present,
or  represented, and not entitled to vote on such proposals, will not be counted
as votes for or against, and will  not be included in calculating the number  of
votes necessary for approval of such proposals.
 
                             CIBA-GEIGY TRANSACTION
 
    Effective January 1, 1995, Ciba-Geigy Limited ("Ciba"), a Swiss corporation,
and  the  Company  closed a  transaction  (the  "Closing") to  form  a strategic
partnership. Chiron and Ciba will collaborate to discover, develop,  manufacture
and  market biotechnology and other healthcare products as the parties may agree
from time to time on  a global scale. Under the  terms of the agreement,  Chiron
and  Ciba  will  be preferred  partners  seeking to  leverage  the complementary
strengths of the  two companies  through cooperative approaches,  but each  will
remain  independent to  pursue projects outside  of the partnership.  As part of
that transaction,  Ciba  purchased through  a  partial tender  offer  11,860,467
shares  of the Company's outstanding Common  Stock from the stockholders at $117
per share. Ciba  also acquired 6,600,000  new shares of  Common Stock issued  by
Chiron  in  exchange  for  all  of Ciba's  ownership  interest  in  Ciba Corning
Diagnostics Corp., The Biocine Company  and Biocine S.p.A. These newly  acquired
shares  of Common Stock,  when combined with  the approximately 1,367,372 shares
that Ciba already held,  result in Ciba owning  approximately 47 percent of  the
outstanding Common Stock of the Company as of February 29, 1996.
 
    On  November  20,  1994, Chiron  and  Ciba  entered into  an  agreement (the
"Governance  Agreement")  which  contains   terms  relating  to  the   corporate
governance  of  the  Company  following  the  Closing  and  the  acquisition and
disposition of  securities of  the Company  by Ciba  and its  subsidiaries.  The
Governance  Agreement provides  that, from and  after the Closing,  the Board of
Directors of the Company will be comprised of 11 directors (each, a "Director"),
and the  number of  directors may  be  increased only  as described  below.  The
Nominating Committee of the Board of Directors (the "Nominating Committee") will
nominate  persons to serve as  Directors as described below,  and each person so
nominated will be  included in management's  slate of nominees  for each  annual
meeting  of the  stockholders of the  Company. The  Governance Agreement further
provides that the Nominating Committee will  nominate three persons to serve  as
management Directors (each a "Management Director"), two of whom will be the two
most  senior executives of the Company and the third of whom will be an employee
of the Company (or a person otherwise designated as a Management Director by the
Nominating Committee). In addition, Ciba will have the right to designate  three
persons to serve as Directors (each, an "Investor Director"), any of whom may be
officers  or employees of Ciba or its affiliates. If, however, Ciba's Percentage
Interest (as defined below) for any period is less than 30 percent but at  least
20 percent, during that period Ciba will instead have the right to designate for
nomination  only two Investor  Directors, and, if  Ciba's Percentage Interest is
less than
 
                                       2
<PAGE>
20 percent for any period, during that  period Ciba will instead have the  right
to  designate for nomination only one Investor Director. As used herein, "Ciba's
Percentage Interest" means  the percentage  of voting power,  determined on  the
basis  of the  number of  shares of voting  stock actually  outstanding, that is
controlled directly or indirectly by Ciba or any subsidiary of Ciba (other  than
the  Company and its subsidiaries),  including by beneficial ownership. Finally,
the Nominating Committee will nominate the remaining Directors (the "Independent
Directors"), each  of whom  must  have an  outstanding reputation  for  personal
integrity  and distinguished achievement  in areas relevant  to the Company and,
under the  terms  of  the  Governance  Agreement,  must  meet  certain  criteria
demonstrating  such  person's  independence  from  both  Ciba  and  the Company.
Pursuant to the Governance Agreement, on January 4, 1995, the Board of Directors
elected three  nominees of  Ciba: Dr.  Alex Krauer,  Mr. Pierre  Douaze and  Dr.
Francois L'Eplattenier, to serve on the Board as representatives of Ciba.
 
    Under  the  terms  of the  Governance  Agreement,  Ciba agreed  that  in any
election of  directors or  any meeting  of stockholders  of the  Company  called
expressly  for  the removal  of directors,  so  long as  the Board  of Directors
includes (and  will include  after  any such  removal)  the number  of  Investor
Directors contemplated by the Governance Agreement, Ciba and its affiliates will
be  present for purposes of establishing a quorum and will vote all their shares
of voting stock (i) in favor of  any nominee or director selected or removed  in
accordance  with the terms of the Governance Agreement, (ii) in favor of removal
of any Director in circumstances where the number of Investor Directors is  more
than  required under the terms of that Agreement and (iii) otherwise against the
removal of any director designated in accordance with the Governance  Agreement.
In any other matter submitted to a vote of the stockholders of the Company, Ciba
may  vote any or all of its shares in its sole discretion unless such matter was
approved by Ciba or a majority of the Investor Directors in accordance with  the
terms  of the Governance Agreement,  in which case Ciba  and its affiliates will
cast all their votes in favor of such matter. Because a majority of the Investor
Directors have approved the amendment  of the Company's Restated Certificate  of
Incorporation  and the amended 1991 Stock Option  Plan which are the subjects of
Proposals 2 and  3 of this  Proxy Statement, the  Company anticipates that  Ciba
will cast all of its votes in favor of such matters at the Annual Meeting.
 
    STANDSTILL.   Under the terms of the Governance Agreement, during the period
beginning at  the  Closing and  terminating  at  January 15,  2000  (the  "First
Standstill  Period"), Ciba has agreed that  it will not, directly or indirectly,
purchase or otherwise acquire any Equity Securities (as defined below) from  any
person  other than the Company unless (i)  such acquisition is a Market Purchase
(as defined  below) and  (ii) immediately  after such  purchase or  acquisition,
Ciba's  Percentage Interest would  not exceed the greatest  of (A) 49.9 percent,
(B) the highest  Ciba's Percentage  Interest resulting from  any acquisition  by
Ciba or its affiliates of Equity Securities that has been approved by a majority
of  the  Independent Directors  as described  below and  (C) the  highest Ciba's
Percentage Interest immediately following any action by the Company (including a
purchase by the  Company of outstanding  Equity Securities or  a sale of  Equity
Securities  to  Ciba or  its affiliates  by the  Company) that  increases Ciba's
Percentage Interest.
 
    As defined in the  Governance Agreement, "Equity  Securities" means (i)  the
Common  Stock and any other voting stock  of the Company, (ii) any securities of
the Company convertible into  or exchangeable for Common  Stock or other  voting
stock  or  (iii) any  options, rights  or warrants  (or any  similar securities)
issued by the Company to acquire Common Stock or other voting stock, and "Market
Purchase"  means  an  acquisition  of  Equity  Securities  that  is  within  the
definition  of "Rule  10b-18 Purchase"  under Rule  10b-18 under  the Securities
Exchange Act of 1934  (the "Exchange Act")  as in effect  on November 20,  1994,
that satisfies the conditions of paragraph (b) of Rule 10b-18.
 
    During  the period beginning at  the end of the  First Standstill Period and
terminating, if  ever, at  the date  that  Ciba and  its affiliates  become  the
beneficial  owners  of all  outstanding shares  of  Equity Securities,  Ciba has
further agreed that it will not,  directly or indirectly, purchase or  otherwise
acquire  any Equity Securities from any person other than the Company unless (i)
such acquisition is a Market Purchase  and (ii) immediately after such  purchase
or  acquisition, Ciba's Percentage Interest would not exceed the greatest of (A)
55 percent,  (B)  the highest  Ciba's  Percentage Interest  resulting  from  any
acquisition  by  Ciba  or its  affiliates  of  Equity Securities  that  has been
approved by a majority of the Independent Directors as
 
                                       3
<PAGE>
described below  and  (C) the  highest  Ciba's Percentage  Interest  immediately
following  any action  by the  Company (including a  purchase by  the Company of
outstanding Equity Securities  or a  sale of Equity  Securities to  Ciba or  its
affiliates by the Company) that increases Ciba's Percentage Interest.
 
    Except  with  respect  to  a  Buyout  Transaction  (as  defined  below), the
Governance Agreement provides that any  other purchase or acquisition of  Equity
Securities by Ciba or its affiliates from any person other than the Company will
require the approval of a majority of the Independent Directors acting solely in
the  interest of the unaffiliated stockholders and in granting such approval the
Independent Directors, unless a majority of them decide otherwise, will  require
a  purchase price for such Equity Securities reflecting a proportionate share of
then prevailing Third Party Sale Value  (as defined below), except that no  such
purchase may increase Ciba's Percentage Interest above 79.9 percent.
 
    As  defined in the Governance Agreement,  "Third Party Sale Value" means the
value that an  unaffiliated third party  would be expected  (based on  financial
analyses  generally used by investment bankers  in the preparation of a fairness
opinion for an acquisition transaction) to pay for all the Equity Securities  of
the  Company in an arm's-length transaction negotiated by a willing seller and a
willing buyer.
 
    BUYOUT TRANSACTION.  The Governance Agreement provides that, notwithstanding
the  standstill  provisions  described  above,  at  any  time  after  the  sixth
anniversary  of  the Closing,  but  as early  as  the fifth  anniversary  of the
Closing, if certain conditions exist, Ciba  may propose and consummate a  tender
offer,  merger, sale  of substantially  all of  the Company's  assets or similar
transaction involving  Ciba or  one of  its affiliates  and the  Company or  the
unaffiliated  stockholders  that (1)  offers  each unaffiliated  stockholder the
opportunity to dispose  of all Equity  Securities owned by  such stockholder  or
otherwise  provides for the  acquisition of all Equity  Securities owned by such
stockholder, in  each  case  for  consideration  reflecting  such  stockholder's
proportionate  share of consideration  at least equal to  Third Party Sale Value
(the "Third Party Sale  Value Consideration") and (2)  for each class of  Equity
Securities,  provides the same consideration for each security within such class
(any such transaction being referred to herein as a "Buyout Transaction"). Under
the terms  of  the  Governance  Agreement, a  Buyout  Transaction  may  only  be
consummated pursuant to certain procedures specified therein.
 
    The  Governance  Agreement  provides  that  until  Ciba  and  its affiliates
beneficially own  all outstanding  shares  of Equity  Securities, Ciba  and  its
subsidiaries  will  not  (i)  make,  or  in  any  way  participate,  directly or
indirectly, in any "solicitation" of "proxies"  to vote (as such terms are  used
in the proxy rules of the Securities and Exchange Commission) or seek to advise,
encourage  or influence any person  or entity with respect  to the voting of any
shares of capital stock of the  Company, initiate, propose or otherwise  solicit
stockholders  of  the  Company  for  the approval  of  one  or  more stockholder
proposals  or  induce  or  attempt   to  induce  any  other  individual,   firm,
corporation,  partnership or other entity  to initiate any stockholder proposal;
or (ii) deposit any shares  of voting stock into a  voting trust or subject  any
shares  of voting  stock to  any arrangement  or agreement  with respect  to the
voting of  such  securities or  form,  join or  in  any way  participate  in  or
otherwise  encourage  the formation  of, with  respect to  any shares  of Common
Stock, any group of persons formed for the purpose of acquiring, holding, voting
or disposing of voting stock which would be required under Section 13(d) of  the
Exchange  Act, and the rules and regulations  thereunder, to file a statement on
Schedule 13D with  the Commission as  a "person" within  the meaning of  Section
13(d)(3)  of  the Exchange  Act if  such group  beneficially owned  voting stock
representing more than 5 percent of any class of voting stock then outstanding.
 
                                       4
<PAGE>
                             PRINCIPAL STOCKHOLDERS
 
    The following are the only persons  known by Chiron to own beneficially,  as
of  February 29, 1996, 5 percent or more of the outstanding shares of its Common
Stock.
 
    On February 29, 1996,  there were 42,108,818 shares  of Chiron Common  Stock
outstanding.
 
<TABLE>
<CAPTION>
                                                                                 AMOUNT AND
                                                                                  NATURE OF
                                                                                 BENEFICIAL       PERCENT
NAME AND ADDRESS OF BENEFICIAL OWNER                                            OWNERSHIP (1)    OF CLASS
- -----------------------------------------------------------------------------  ---------------  -----------
<S>                                                                            <C>              <C>
Ciba-Geigy Limited ..........................................................    19,829,949(2)       47.1%
 Klybeckstrasse CH-4002
 Basel, Switzerland
Jennison Associates Capital Corp. (3) .......................................     2,220,027           5.3%
 466 Lexington Avenue
 New York, NY 10017
The Prudential Insurance Company of America (4) .............................     2,227,704           5.3%
 Prudential Plaza
 Newark, NJ 07102-3777
</TABLE>
 
- ------------------------
(1) Under the terms of the Governance Agreement, Ciba is permitted to acquire up
    to  49.9 percent of the Company's  Common Stock through market purchases and
    to participate  pro rata  in  certain issuances  of  new securities  by  the
    Company.  In addition,  in certain  instances, under  the terms  of a Market
    Price Option Agreement between  Ciba and the Company,  Ciba is permitted  to
    purchase  Common Stock  directly from the  Company upon  the satisfaction of
    certain  conditions.  See  "Related   Transactions"  below  for  a   further
    discussion of Chiron's relationships with Ciba.
 
(2) Includes  approximately 87,007  shares of  the Company's  Common Stock which
    underlie a convertible subordinated note held by Ciba.
 
(3) According to a Schedule 13G sent to the Company, Jennison Associates Capital
    Corp. ("Jennison"),  an  investment adviser,  was  the beneficial  owner  of
    2,220,027  shares  of the  Company's stock  at  December 31,  1995. Jennison
    reports sole  voting power  as to  271,981 shares  of the  Company's  stock,
    shared voting power as to 1,672,903 shares of the Company's stock and shared
    dispositive power as to 2,220,027 shares of the Company's stock.
 
(4) According  to a Schedule  13G sent to the  Company, The Prudential Insurance
    Company of America ("Prudential"),  an insurance company, broker-dealer  and
    investment  adviser, was  the beneficial  owner of  2,227,704 shares  of the
    Company's stock at  December 31,  1995. Prudential reports  sole voting  and
    dispositive power as to 200,328 shares of the Company's stock, shared voting
    power  as to 1,752,233 shares of  the Company's stock and shared dispositive
    power as to 2,027,376 shares of the Company stock.
 
                                       5
<PAGE>
                        SECURITY OWNERSHIP OF MANAGEMENT
 
    The following table sets forth the  beneficial ownership of Common Stock  of
Chiron  as of February  29, 1996, by each  director and nominee  to the Board of
Directors,  the  Chief  Executive  Officer  and  the  four  other  most   highly
compensated  executive  officers and,  as  a group,  by  such persons  and other
executive officers of Chiron. All shares are subject to the named person's  sole
voting and investment power.
 
<TABLE>
<CAPTION>
                                                                                AMOUNT AND
                                                                                 NATURE OF
                                                                                BENEFICIAL     PERCENT OF
NAME OF BENEFICIAL OWNER                                                       OWNERSHIP (1)   CLASS (2)
- -----------------------------------------------------------------------------  -------------  ------------
<S>                                                                            <C>            <C>
Lewis W. Coleman.............................................................        14,273        *
Pierre Douaze................................................................         4,250        *
Donald A. Glaser.............................................................        97,457        *
William G. Green.............................................................        81,369        *
Alex Krauer..................................................................         4,250        *
Francois L'Eplattenier.......................................................         4,250        *
Edward E. Penhoet............................................................       256,456        *
William J. Rutter............................................................       608,628         1.4%
Henri Schramek...............................................................        15,760        *
Jack W. Schuler..............................................................        29,603        *
Pieter J. Strijkert..........................................................        13,656        *
Dennis L. Winger.............................................................        75,494        *
C. William Zadel.............................................................           -0-        *
All directors and executive officers as a group (29 persons).................     1,667,348         4.0%
</TABLE>
 
- ------------------------
(1) This   disclosure  is  made  pursuant   to  certain  rules  and  regulations
    promulgated by  the  Securities  and Exchange  Commission  and,  in  certain
    instances, the number of shares shown as being beneficially owned may not be
    deemed  to be beneficially  owned for other  purposes. Includes shares which
    are subject to options or warrants exercisable on or before April 29,  1996,
    in  the following  amounts: Mr.  Coleman, 13,656  shares; Mr.  Douaze, 4,250
    shares; Dr. Glaser,  31,802 shares;  Mr. Green, 70,344  shares; Dr.  Krauer,
    4,250  shares; Dr. L'Eplattenier, 4,250 shares; Dr. Penhoet, 163,095 shares;
    Dr. Rutter, 196,694 shares; Dr. Schramek, 15,760 shares; Mr. Schuler, 28,800
    shares; Dr. Strijkert,  13,656 shares;  Mr. Winger, 16,473  shares; and  all
    directors and executive officers as a group, 896,059 shares.
 
(2) Percentage  of  outstanding Common  Stock and  of Common  Stock that  may be
    acquired upon  exercise of  outstanding options  and warrants  on or  before
    April  29,  1996,  by the  persons  named  above and  by  all  directors and
    executive officers as a  group. The asterisk (*)  indicates that the  shares
    beneficially   owned  represent  less   than  one  percent   of  the  shares
    outstanding.
 
                                  PROPOSAL 1:
                             ELECTION OF DIRECTORS
 
    Chiron has three  classes of directors  serving staggered three-year  terms.
Three directors presently serve in Class I, three directors in Class II and four
directors  in  Class III.  This year,  the  following three  directors presently
serving in Class III are nominated to be reelected for three-year terms expiring
in 1999: Dr. William J. Rutter and Messrs. Jack W. Schuler and Lewis W. Coleman.
See "Ciba-Geigy Transaction" at pp. 2-4 for a discussion of matters relating  to
Ciba's  voting  of shares  held  by it  and its  affiliates  in any  election of
directors. Effective December 31, 1995, Dr. Gilbert Amelio, a Class II director,
resigned from the Board of Directors, creating  a vacancy that has not yet  been
filled.  The  Company  understands that  Dr.  L'Eplattenier is  not  expected to
continue to serve as a director following consummation of the pending merger  of
Ciba  and Sandoz Ltd. and, accordingly, will not stand for reelection as a Class
III director. Under the Governance Agreement, Ciba may designate a successor for
Dr.   L'Eplattenier.    Until    a    successor   is    designated    by    Ciba
 
                                       6
<PAGE>
and  duly nominated  and elected,  the position held  by Dr.  L'Eplattenier as a
Class III director will be vacant. If a successor is designated by Ciba and duly
nominated by the Board prior to the  Annual Meeting, the proxies intend to  vote
all proxies received by them for such nominee.
 
           THE BOARD OF DIRECTORS RECOMMENDS A VOTE FOR EACH NOMINEE.
 
    The  persons named on the enclosed proxy (the "proxy holders") will vote for
election of the above-named nominees unless you have withheld authority for them
to do so on your proxy card. In the unanticipated event that a nominee is unable
to or declines to  serve as a director  at the time of  the Annual Meeting,  the
proxies will be voted for any nominee named by the present Board of Directors to
fill the vacancy. As of the date of this Proxy Statement, the Board of Directors
is  not aware of any nominee who is unable  to or who will decline to serve as a
director. In the  event that additional  persons are nominated  for election  as
directors, the proxy holders intend to vote all proxies received by them for the
nominees listed above.
 
    Information  as to the  nominees, and as  to each other  director whose term
will continue after the 1996 Annual Meeting of Stockholders, is given below.
 
<TABLE>
<CAPTION>
                                                                                                              SERVED AS
                    NAME                           AGE                  PRINCIPAL OCCUPATION               DIRECTOR SINCE
- ---------------------------------------------      ---      ---------------------------------------------  ---------------
<S>                                            <C>          <C>                                            <C>
CLASS III (1999 CLASS)
  Lewis W. Coleman...........................          54   Senior Managing Director, Co-Director                  1991
                                                             Investment Banking,
                                                             Montgomery Securities
  William J. Rutter..........................          67   Chairman, Chiron Corporation                           1981
  Jack W. Schuler............................          55   Chairman, Stericycle Corporation                       1991
 
CLASS I (1997 CLASS)
  Donald A. Glaser...........................          69   Professor of Physics, of Molecular                     1991
                                                             Biology, and of Neuroscience,
                                                             University of California, Berkeley
  Alex Krauer................................          65   Chairman of the Board and Chief                        1995
                                                             Executive Officer, Ciba-Geigy
                                                             Limited
  Pieter J. Strijkert........................          60   Chairman of the Board, IntroGene                       1987
                                                             b.v., Pharming b.v. and New Drug
                                                             Research Foundation
 
CLASS II (1998 CLASS)
  Pierre Douaze..............................          56   Member of the Executive Committee                      1995
                                                             of management, Ciba-Geigy Limited
  Edward E. Penhoet..........................          55   President and Chief Executive Officer,                 1981
                                                             Chiron Corporation
  Henri Schramek.............................          77   Retired; Former Member of the                          1989
                                                             Board of Directors, Ciba-Geigy
                                                             Limited
</TABLE>
 
CLASS III (1999 CLASS)
 
    LEWIS W. COLEMAN is Senior  Managing Director and Co-Director of  Investment
Banking  at Montgomery Securities.  Prior to joining  Montgomery Securities, Mr.
Coleman was Vice  Chairman of  the Board of  Directors and  the Chief  Financial
Officer  of BankAmerica Corp.  from February 1993 to  December 1995. Mr. Coleman
joined Bank of  America in  1986 as Executive  Vice President  and Chief  Credit
Officer, World Banking Group. He also headed the Capital Markets Group and later
served  from 1990 to  1993 as Vice Chairman  of the Board and  Head of the World
Banking Group at Bank of America.
 
                                       7
<PAGE>
    WILLIAM J.  RUTTER is  a cofounder  of the  Company and  has served  as  its
Chairman  of the Board since the Company's inception. In 1969, Dr. Rutter joined
the faculty  of  the  University  of  California,  San  Francisco  ("UCSF"),  as
Hertzstein   Professor,  and  he  served  as   Chairman  of  the  Department  of
Biochemistry and Biophysics at UCSF from 1969 to 1982. From August 1983  through
April  1989, in addition to  his responsibilities at Chiron,  Dr. Rutter was the
Director of the  Hormone Research  Institute at UCSF.  In May  1989, Dr.  Rutter
became  a full-time employee of Chiron and consequently vacated the Directorship
of the Hormone  Research Institute. He  became Professor emeritus  in 1991.  Dr.
Rutter is a member of the Board of Directors of Ciba.
 
    JACK  W.  SCHULER  is Chairman  of  Stericycle Corporation,  a  company that
processes, sterilizes and recycles medical  waste. Prior to joining  Stericycle,
Mr.  Schuler was  President and Chief  Operating Officer  of Abbott Laboratories
("Abbott") from 1987 to 1989. He joined Abbott in 1972 as Director of Sales  and
Marketing  for the diagnostics  division, and held a  series of diagnostic sales
and management positions. He served on  the Abbott Board of Directors from  1985
to  1989. Mr.  Schuler is a  member of the  Board of Directors  of Somatogen and
Medtronic, Inc.
 
CLASS I (1997 CLASS)
 
    DONALD A. GLASER was a founder of  Cetus Corporation, a member of its  Board
of Directors from 1971 to 1991, and Chairman of the Board of Scientific Advisors
of  Cetus.  He  has served  on  the  faculty at  the  University  of California,
Berkeley, since 1959. Dr. Glaser received a Nobel Prize in Physics in 1960.
 
    ALEX KRAUER has been the Chairman  of the Board and Chief Executive  Officer
of Ciba since 1987.
 
    PIETER  J.  STRIJKERT is  Chairman of  the Board  of three  Dutch companies:
IntroGene b.v., Pharming b.v. and  New Drug Research Foundation. Previously,  he
was  a member of the Management Board  of Gist-Brocades N.V., a fermentation and
pharmaceutical company headquartered in the  Netherlands, from 1985 until  1993,
and  was Chairman of  the Supervisory Board  of International Bio-Synthetics BV,
now called Bio-Specialties Division, a division of Gist-Brocades N.V.
 
CLASS II (1998 CLASS)
 
    PIERRE DOUAZE has been a member of the Executive Committee of management  of
Ciba since 1991 and Head of the Pharma Division of Ciba since 1989.
 
    EDWARD E. PENHOET, a cofounder of the Company and a director since 1981, has
served as Chief Executive Officer since the Company's inception. Dr. Penhoet has
been  a  faculty member  of  the Biochemistry  Department  at the  University of
California, Berkeley, for 24 years. Since 1983, he has been an Adjunct Professor
at that university.
 
    HENRI SCHRAMEK became a director of the  Company in April 1989. He was  with
Ciba  for thirty-eight years, having retired  from operations in 1983 and having
served as a Member of the Board of  Directors of that company from 1983 to  1988
and as Vice Chairman of the Board of Directors from 1987 until 1988.
 
                           COMPENSATION OF DIRECTORS
 
    The  Company pays each  non-employee director a retainer  fee of $16,000 per
year; an additional fee  of $2,000 for  each meeting of  the Board of  Directors
attended  in person; an additional fee of $500 for each telephone meeting of the
Board of Directors; and a fee of $200 per hour, to a maximum of $1,000 per  day,
for  time spent on meetings of Committees of the Board of Directors on days when
no meeting  of the  Board  of Directors  is held.  The  Company also  pays  each
non-employee  director serving  as chairman  of one  of the  Board Committees an
additional retainer of $5,000 per year.
 
    Under the  Company's  1991  Stock  Option  Plan  (the  "Option  Plan"),  the
automatic  option grant  program provides  that each  non-employee director will
automatically be granted a non-statutory stock option ("Automatic Option Grant")
to purchase 3,000 shares of  the Company's Common Stock on  the last day of  the
second  quarter of each fiscal year, with an option price per share equal to the
fair market value (as defined  in the plan) of the  Common Stock on that  annual
grant date. The option exercise price is payable in
 
                                       8
<PAGE>
cash,  or in shares of Chiron Common Stock held for at least six months, or with
the proceeds of a same day sale of  the option shares. Each person who is  newly
elected  or appointed as a  non-employee member of the  Board of Directors after
the effective date of the  Option Plan (other than  on an automatic grant  date)
will  receive, on the date of such  election or appointment, an Automatic Option
Grant to purchase a pro  rata number of shares  of Common Stock. Each  Automatic
Option Grant will have a term of ten years measured from its grant date and will
be  exercisable at any time for all or any part of the number of granted shares.
The shares purchased under  the options are subject  to repurchase by Chiron  at
the  original  exercise price  in the  event a  non-employee director  ceases to
provide service to  Chiron or  its subsidiaries as  a director,  an employee,  a
consultant  or an independent  contractor. Chiron's repurchase  right will lapse
(and the optionee's interest in the purchased  shares will vest) in a series  of
equal  annual installments over a five-year period measured from the date of the
automatic grant,  provided  the optionee  continues  to provide  such  services.
Chiron's  repurchase right  will lapse  in its  entirety, and  full vesting will
occur, if, while providing  such services, the optionee  dies or is  permanently
disabled.  In the event the optionee ceases to provide services to Chiron or its
subsidiaries as  a  director,  an  employee,  a  consultant  or  an  independent
contractor,  the option may be exercised for  a period of three months after the
date of such cessation of services (12 months in the case of cessation by reason
of disability or  death). Discretionary provisions  of the Option  Plan are  not
applicable  to the Automatic Option Grants. On  the effective date of the Option
Plan, the terms and conditions of outstanding automatic option grants under  the
Company's  1982 Stock Option Plan were  conformed to the Automatic Option Grants
under the Option Plan; however,  the term of the  options was not extended.  See
Proposal  3 below at p. 29 for a  discussion of amendments to the Company's 1991
Stock Option  Plan  whereby the  formula  for granting  annual  automatic  stock
options  to non-employee directors  is changed and an  annual grant of automatic
share rights for non-employee directors is added.
 
    Of the current  directors, Dr. Penhoet  and Dr. Rutter  are not eligible  to
receive  Automatic Option Grants because they  are employees of the Company. Mr.
Schuler has waived his right to receive these grants for so long as he serves as
consultant to the Company as described in the following paragraph.
 
    In December 1991,  the Company  retained Mr.  Schuler as  a consultant.  The
Company  agreed to pay Mr.  Schuler $200,000 per year  of consulting, payable in
monthly increments, and granted Mr. Schuler options to acquire 40,000 shares  of
Chiron Common Stock, vesting on a pro rata basis over four years.
 
    In  May 1992,  the Company  retained Dr. Donald  Glaser to  consult with and
advise the  Company in  the  fields of  general  automation and  technology  and
neurobiology  over a period of three years  ending in January 1995, at an annual
retainer of not less than $45,000.
 
              INFORMATION CONCERNING BOARD MEETINGS AND COMMITTEES
 
    The Board of Directors of the Company held a total of seven meetings  during
the  fiscal year  ended December  31, 1995.  To assist  in the  discharge of its
responsibilities,  the  Board   of  Directors  has   designated  four   standing
committees.  They  are a  Finance  and Audit  Committee  (now called  the "Audit
Committee"), a Compensation Committee, an Employee Stock Option Committee and  a
Nominating Committee. The Governance Agreement provides that each such committee
will  generally continue  to have the  same responsibilities as  held before the
Ciba transaction. The number of Investor Directors on each committee (other than
the Nominating Committee)  will generally be  the same proportion  of the  total
membership  of such  committee as  the number  of Investor  Directors is  of the
entire Board of Directors.
 
    The Audit  Committee is  responsible for  finance, budget,  audit,  internal
control, accounting, and related matters. This Committee, which consisted of Mr.
Coleman,  as Chairman,  Dr. Amelio  and Dr.  Krauer, held  four meetings  in the
Company's last fiscal year. Following Dr. Amelio's resignation from the Board of
Directors on December 31, 1995, the Board of Directors appointed Mr. Schuler  as
a member of the Audit Committee.
 
    The  Compensation  Committee's  principal  functions  are  to  evaluate  the
performance of  the  Company's executive  officers,  to consider  and  plan  for
executive  officer succession, to review  and approve executive compensation, to
review the  design  and  competitiveness of  the  Company's  compensation  plans
generally
 
                                       9
<PAGE>
and  to  administer the  Company's stock  option,  stock purchase  and executive
officer variable cash compensation plans pursuant  to the terms of those  plans.
The  members of  the Compensation Committee  are non-employee  directors and are
ineligible to participate in any of the plans or programs which are administered
by the Committee. This  Committee, which consisted of  Dr. Amelio, as  Chairman,
and  Drs. Strijkert, Schramek and Krauer and  Mr. Coleman, held four meetings in
the Company's last fiscal year.  Following Dr. Amelio's resignation on  December
31,  1995, the Board of Directors appointed  Mr. Coleman interim chairman of the
Compensation Committee. The Board has also delegated to an Employee Stock Option
Committee, composed of Drs. Penhoet and Rutter, authority to make routine  stock
option grants calculated according to the policies, procedures and methodologies
approved  from time  to time  by the Compensation  Committee to  any employee or
consultant except executive officers and directors.
 
    In February 1994, the Board of Directors established a Nominating Committee.
The Nominating Committee is responsible  for matters relating to composition  of
the  Board of Directors including  recruitment, nomination and succession. Under
the terms of the Governance  Agreement, the Nominating Committee will  initially
be  comprised  of two  Independent Directors,  one  Management Director  and one
Investor Director. After the fifth anniversary of the Closing, so long as Ciba's
Percentage Interest is at least 40 percent, an additional Investor Director will
serve on the Nominating  Committee. While the Nominating  Committee will act  by
the  vote of a majority  of its members, the  Governance Agreement provides that
after the  fifth  anniversary of  the  Closing,  so long  as  Ciba's  Percentage
Interest  is  at  least  40  percent, the  Management  Director  serving  on the
Nominating Committee will  not be able  to break  any tie vote  between all  the
Investor  Director members,  on the one  hand, and all  the Independent Director
members, on the other hand. In  addition, after the eleventh anniversary of  the
Closing,  so long  as Ciba's  Percentage Interest  is at  least 49  percent, the
Governance  Agreement  provides  that  the  Investor  Director  members  of  the
Nominating Committee will have a deciding vote to break any tie vote between all
the Investor Director members, on the one hand, and all the Independent Director
members,  on the other hand (meaning that, with respect to any motion before the
committee, if  the  two Investor  Director  members vote  one  way and  the  two
Independent  Director  members vote  the  other way,  the  vote of  the Investor
Directors will control).  No procedure  has been established  by the  Nominating
Committee  for  the  consideration  of  nominees  recommended  by  stockholders.
However, stockholders of Chiron are entitled to nominate candidates for director
at the Annual Meeting if they  have complied with the advance notice  procedures
contained  in the Company's Bylaws. The Nominating Committee, which consisted of
Dr. Amelio,  Mr. Coleman,  Dr. Rutter,  Mr. Schuler,  and Dr.  Krauer, held  one
meeting in the Company's last fiscal year.
 
    The  Governance Agreement also contemplates the  creation in the future of a
Strategic Planning Committee with certain responsibilities, described below. The
Governance Agreement provides that the Board  of Directors will set and  approve
measurement standards to evaluate the Company's performance for each fiscal year
of  the Company.  The Governance Agreement  further provides  that the Strategic
Planning Committee of the  Board of Directors will  function from and after  any
fiscal  year  for which  the Company  fails to  meet the  applicable measurement
standards and will continue  to function until the  measurement standards for  a
subsequent  full  fiscal year  are fulfilled.  The Strategic  Planning Committee
will, under the terms of the Governance Agreement, prepare and recommend to  the
Board of Directors a remedial plan intended to restore the Company to compliance
with  applicable measurement standards.  In the event the  Company fails to meet
the measurement  standards  for two  consecutive  fiscal years,  the  Governance
Agreement  provides  that  thereafter  until  the  measurement  standards  for a
subsequent full fiscal year are  fulfilled, in addition to the  responsibilities
of  the  Strategic Planning  Committee described  above, the  Strategic Planning
Committee will have the  delegated power of  the Board of  Directors to set  the
compensation  and  terminate the  employment of  the  executive officers  of the
Company. Under the  terms of  the Governance Agreement,  the Strategic  Planning
Committee  will be comprised of the  three Investor Directors, three Independent
Directors and one  Management Director. While  the Strategic Planning  Committee
will  act by  the vote of  a majority  of its members,  the Governance Agreement
provides  that  the  Management  Director  serving  on  the  Strategic  Planning
Committee  will  not be  able to  break any  tie vote  between all  the Investor
Director members, on the one hand, and all the Independent Director members,  on
the other hand.
 
                                       10
<PAGE>
    Each  director attended more than 75  percent of the combined total meetings
of the Board of Directors and its Committees on which the director served at any
time during the year.
 
                             EXECUTIVE COMPENSATION
 
    The following table sets  forth certain summary  information for the  fiscal
years ended December 31, 1993, 1994 and 1995, concerning compensation paid to or
accrued  by the  Company and  its subsidiaries on  behalf of,  those persons who
were, at December 31, 1995, (i) the  chief executive officer and (ii) the  other
four most highly compensated executive officers of the Company ("named executive
officers"):
 
                           SUMMARY COMPENSATION TABLE
<TABLE>
<CAPTION>
                                                                                               LONG-TERM COMPENSATION
                                                                                            -----------------------------
                                                      ANNUAL COMPENSATION                        AWARD
                                      ----------------------------------------------------  ---------------    PAYOUTS
                                                                            OTHER ANNUAL      SECURITIES     ------------
                                                                            COMPENSATION      UNDERLYING         LTIP
    NAME AND PRINICPAL POSITION         YEAR     SALARY ($)    BONUS ($)         ($)          OPTIONS (#)    PAYOUTS ($)
- ------------------------------------  ---------  -----------  -----------  ---------------  ---------------  ------------
<S>                                   <C>        <C>          <C>          <C>              <C>              <C>
Edward E. Penhoet ..................       1995   $ 397,917    $ 350,000      $  --               62,175        --
 President and Chief                       1994     373,338      300,000         --               35,000        --
 Executive Officer                         1993     323,122      247,754         --               32,000        --
William J. Rutter ..................       1995     397,917      350,000         --               62,175        --
 Chairman                                  1994     373,334      300,000         --               35,000        --
                                           1993     322,917      247,754         --               32,000        --
C. William Zadel (2) ...............       1995     332,923      254,198         --                5,037     $ 325,215(3)
 Vice President and Chief
 Executive Officer, Ciba
 Corning Diagnostics Corp.
William G. Green ...................       1995     326,667      213,200         --               29,475        --
 Senior Vice President, Secretary          1994     311,000      200,000         --               10,000        --
 and General Counsel                       1993     299,621      125,750         --               17,400        --
Dennis L. Winger ...................       1995     263,717      172,250         --               28,675        --
 Senior Vice President, Finance            1994     248,800      150,000         --               10,000        --
 and Administration, and                   1993     238,750      124,860         --               13,900        --
 Chief Financial Officer
 
<CAPTION>
                                        ALL OTHER
                                       COMPENSATION
    NAME AND PRINICPAL POSITION           ($)(1)
- ------------------------------------  --------------
<S>                                   <C>
Edward E. Penhoet ..................  $ 1,426,529
 President and Chief                        4,500
 Executive Officer                          7,075
William J. Rutter ..................    1,426,529
 Chairman                                   4,500
                                            7,075
C. William Zadel (2) ...............    1,178,929(4)
 Vice President and Chief
 Executive Officer, Ciba
 Corning Diagnostics Corp.
William G. Green ...................      616,312
 Senior Vice President, Secretary           4,500
 and General Counsel                        7,075
Dennis L. Winger ...................      151,319
 Senior Vice President, Finance             4,500
 and Administration, and                    6,862
 Chief Financial Officer
</TABLE>
 
- ------------------------------
(1)  "All Other Compensation" includes Company contributions of $4,500 under the
    Company's, or as to Mr. Zadel, a subsidiary's, 401(k) Plan on behalf of each
    of the  named executives  to match  pretax elective  deferral  contributions
    (included under Salary) made by each named executive to such plan and, as to
    Mr.   Zadel,  also  includes  Company   contributions  of  $27,389  under  a
    supplemental executive retirement plan, on  behalf of Mr. Zadel. "All  Other
    Compensation"  for  1995 also  includes as  to Drs.  Penhoet and  Rutter and
    Messrs. Green and Winger the following cash payments from Ciba applicable to
    certain options which first became exercisable in calendar year 1995: Edward
    E. Penhoet -- $1,422,029; William J. Rutter -- $1,422,029; William G.  Green
    -- $611,812 and Dennis L. Winger -- $146,819.
 
(2)  Mr. Zadel was employed by the Company in connection with the acquisition of
    Ciba  Corning  Diagnostics  Corp.  ("CCD")  in  January  1995  and  resigned
    effective December 31, 1995.
 
(3)  Payment under  terms of long-term  performance plan of  CCD, a wholly-owned
    subsidiary of the Company as of  January 1, 1995, which plan was  terminated
    effective December 31, 1994.
 
(4)  Includes $1,147,040 payable to Mr. Zadel  as a result of the termination of
    his employment, effective December 31, 1995. Certain additional amounts  may
    be payable to Mr. Zadel in certain circumstances. See "Related Transactions"
    at pp. 25-26 for a discussion of Mr. Zadel's agreement with the Company.
 
                                       11
<PAGE>
                                 OPTION GRANTS
 
    The following table sets forth certain information regarding grants of stock
options  pursuant to the Company's 1991 Stock Option Plan during the fiscal year
ended December 31, 1995, to the named executive officers. No stock  appreciation
rights were granted under that plan during fiscal year 1995.
 
                       OPTION GRANTS IN LAST FISCAL YEAR
 
<TABLE>
<CAPTION>
                                            INDIVIDUAL GRANTS
                           ---------------------------------------------------       POTENTIAL REALIZED VALUE
                           NUMBER OF                                                 AT ASSUMED ANNUAL RATES
                           SECURITIES   % OF TOTAL                                        OF STOCK PRICE
                           UNDERLYING     OPTIONS                                        APPRECIATION FOR
                            OPTIONS     GRANTED TO     EXERCISE OR                       OPTION TERM (3)
                            GRANTED    EMPLOYEES IN    BASE PRICE   EXPIRATION  ----------------------------------
          NAME               (#)(1)     FISCAL YEAR     ($/SH)(2)      DATE       0% ($)      5% ($)     10% ($)
- -------------------------  ----------  -------------   -----------  ----------  ----------  ----------  ----------
<S>                        <C>         <C>             <C>          <C>         <C>         <C>         <C>
Edward E. Penhoet........    30,000         1.14%      $   62.125     2/24/05   $        0  $1,172,103  $2,970,337
                             32,175         1.23%          49.750     5/18/05            0   1,006,676   2,551,113
William J. Rutter........    30,000         1.14%          62.125     2/24/05            0   1,172,103   2,970,337
                             32,175         1.23%          49.750     5/18/05            0   1,006,676   2,551,113
C. William Zadel.........     5,037         0.19%          51.125     5/31/05            0     161,951     410,415
William G. Green.........    11,000         0.42%          62.125     2/24/05            0     429,771   1,089,124
                             18,475         0.71%          49.750     5/18/05            0     578,037   1,464,858
Dennis L. Winger.........    10,200         0.39%          62.125     2/24/05            0     398,515   1,009,915
                             18,475         0.71%          49.750     5/18/05            0     578,037   1,464,858
</TABLE>
 
- ------------------------------
(1) The options become exercisable as to 25 percent of the granted shares on the
    first  anniversary  of the  date of  grant  and, for  the balance,  in equal
    monthly installments over the 36-month period thereafter, so long as service
    with the Company  or one of  its subsidiaries continues,  except for  option
    grants expiring 5/18/05 which are exercisable as follows: the options become
    exercisable  as to  33 1/3  percent of  the granted  shares after  each year
    commencing  with  1996  in  which  the  Company  satisfies  the  Measurement
    Standards  determined  in  accordance  with  the  terms  of  the  Governance
    Agreement. See "Information Concerning Board Meetings and Committees"  above
    at pp. 9-10 for a description generally of the Measurement Standards. If the
    Measurement   Standards  are  not  met  in  any  year,  the  options  remain
    outstanding, but unvested, until the earlier of (i) 3 years of  satisfaction
    of  the Measurement Standards or (ii) 6 years expire from the date of grant.
    To  the  extent  not  already  exercisable,  the  options  generally  become
    exercisable  in the event of an agreement to dispose of all or substantially
    all of the assets or  outstanding capital stock of  the Company by means  of
    sale,  merger, reorganization or liquidation. However, an outstanding option
    will  not  be  so  accelerated   if,  in  connection  with  such   corporate
    transactions,  the option  is either assumed  or replaced  with a comparable
    option to purchase shares of capital stock of the successor corporation.  As
    a result of Mr. Zadel's resignation effective December 31, 1995, the options
    shown for Mr. Zadel expired unvested at the date of his resignation.
 
(2) Upon   exercise,  the  exercise  price   and  any  related  tax  withholding
    obligations  may  generally  be  paid  in  cash,  or,  in  the  Compensation
    Committee's  discretion, in shares of Common  Stock held by the optionee for
    the requisite period to avoid a charge to Chiron's earnings and valued as of
    the exercise date, or under certain  conditions from the proceeds of a  same
    day   sale  of  the  shares  acquired  upon  exercise  of  the  option.  The
    Compensation Committee may  also assist an  optionee in the  exercise of  an
    option  by authorizing a  loan from the  Company for the  purchase price and
    related tax obligations.
 
(3) In accordance with Securities  and Exchange Commission rules, these  columns
    reflect  hypothetical gains  or "option  spreads" that  would exist  for the
    respective options. These rules require that  the gains be based on  assumed
    rates  of annual  compounded stock  price appreciation  of 5  percent and 10
    percent from the date the options were granted over the full ten-year option
    term. The market price of Chiron Common  Stock in May 2005 would be  $101.20
    and  $161.14 per share for the first group of options and $81.04 and $129.04
    for the second group of options,  respectively, at 5 percent and 10  percent
    annual  compounded rates  of appreciation,  regarding option  grants to Drs.
    Penhoet and Rutter and Messrs. Green  and Winger and $83.28 and $132.61  per
    share,  respectively, at 5 percent and 10 percent annual compounded rates of
    appreciation, regarding the  option granted to  Mr. Zadel. There  can be  no
    assurance  that these assumed rates of appreciation or any appreciation will
    occur.
 
                                       12
<PAGE>
               OPTION EXERCISES AND FISCAL YEAR-END OPTION VALUES
 
    The following table provides information with respect to the named executive
officers as to option exercises by them in fiscal year 1995 and the  unexercised
options  held by  them at  the end  of fiscal  year 1995.  No stock appreciation
rights were exercised in fiscal year 1995.
 
   AGGREGATED OPTION EXERCISES IN LAST FISCAL YEAR AND FISCAL YEAR-END OPTION
                                     VALUES
 
<TABLE>
<CAPTION>
                                                                          NUMBER OF SECURITIES         VALUE OF UNEXERCISED
                                                                         UNDERLYING UNEXERCISED            IN-THE-MONEY
                                                                         OPTIONS AT FY-END (#)       OPTIONS AT FY-END ($)(1)
                                  SHARES ACQUIRED        VALUE        ----------------------------  --------------------------
             NAME                 ON EXERCISE (#)   REALIZED ($)(1)(2) EXERCISABLE  UNEXERCISABLE   EXERCISABLE  UNEXERCISABLE
- -------------------------------  -----------------  ----------------  -----------  ---------------  -----------  -------------
<S>                              <C>                <C>               <C>          <C>              <C>          <C>
Edward E. Penhoet..............         52,947         $4,449,279        143,438         97,790     $10,944,547   $ 5,277,659
William J. Rutter..............         74,348          7,162,788        177,037         97,790      14,825,659     5,277,659
C. William Zadel...............              0                  0              0              0               0             0
William G. Green...............         40,821          3,255,474         65,001         41,053       4,635,759     2,227,475
Dennis L. Winger...............         92,054          5,969,583         11,507         39,014         549,047     2,114,395
</TABLE>
 
- ------------------------------
(1) Value realized is equal to market  price of shares on date of exercise  less
    exercise  price and value of  unexercised in-the-money options is calculated
    based on  market  price  of  shares at  fiscal  year-end  ($111.3125),  less
    exercise  price, with the following exception:  with respect to options held
    by the  named executive  officers on  November 20,  1994 that  first  become
    exercisable  before  or after  1995, each  optionee,  except Mr.  Zadel, was
    granted the right to surrender for cancellation, that portion of such option
    relating to 37.33  percent of  the underlying shares  in return  for a  cash
    payment from Ciba equal to (A) the difference between $117 per share and the
    exercise  price per  share of  such option multiplied  by (B)  the number of
    shares with respect to which such option is so surrendered and canceled.  Of
    the  total amounts listed under the  heading "Value Realized", the following
    amounts reflect the exercise of such  rights by each of the named  executive
    officers,  except  Mr. Zadel,:  Edward  E. Penhoet,  $3,814,755;  William J.
    Rutter,  $7,162,788;  William  G.  Green,  $2,493,599;  Dennis  L.   Winger,
    $3,424,533.  The  FY-End Value  for each  of  the named  executive officers,
    except Mr. Zadel, includes the following amounts that could be realized upon
    the exercise of the above-discussed  rights: Edward E. Penhoet:  Exercisable
    --  $1,192,068, Unexercisable -- $727,401; William J. Rutter: Exercisable --
    $0,  Unexercisable  --  $727,401;  William  G.  Green:  Exercisable  --  $0,
    Unexercisable   --   $220,354;  Dennis   L.   Winger:  Exercisable   --  $0,
    Unexercisable -- $191,214.
 
(2) As described below at p. 24 under "Related Transactions," under the terms of
    the Investment Agreement,  as amended,  Ciba paid interest  to officers  and
    directors  of the Company  in connection with their  exercise of the payment
    rights described in footnote 1, including the following amounts to the named
    executive  officers:  Edward  E.  Penhoet,  $128,989;  William  J.   Rutter,
    $214,295; William G. Green, $77,213; Dennis L. Winger, $90,538.
 
                               PENSION AGREEMENTS
 
    The  Company has entered into supplemental pension agreements with two named
executives: William G. Green and Dr. William J. Rutter.
 
    Mr. Green's supplemental  pension agreement  is a monthly  benefit for  life
beginning  at  age  60. The  benefit  is  based on  an  initial  contribution of
$110,000, plus an annual contribution for  each year of service until Mr.  Green
is  age 60, such that the annual contribution when added to the maximum employee
and Company matching contribution under the Company's 401(k) Plan and any future
retirement benefit  shall  not  be  less than  $20,000.  This  amount  shall  be
increased by an assumed 7 percent interest rate compounded annually. Taking into
account  certain  assumptions  about  Internal  Revenue  Code  limitations,  and
assuming Mr. Green makes the maximum 401(k) contribution under the Chiron 401(k)
Plan, and receives the  maximum matching contribution  each year, the  actuarial
equivalent of Mr. Green's benefit at age 65 would be $48,921 annually for life.
 
    Dr.  Rutter's benefit is meant  to indemnify Dr. Rutter,  up to an amount of
$10,000 in any  twelve-month period,  for any University  of California  pension
benefits  he loses by  reason of his  change in status  with the University from
full-time to part-time. From  age 65, Dr. Rutter  would receive annual  payments
for  life of approximately $6,084,  increased each year by  a 2.5 percent annual
cost of living adjustment.
 
    In addition, at age 65, Mr. Zadel is entitled to a monthly benefit for  life
of $6,046 under CCD's pension plan and supplemental retirement plan, under which
plans no further benefits are accruing.
 
                                       13
<PAGE>
          COMPENSATION COMMITTEE INTERLOCKS AND INSIDER PARTICIPATION
 
    As  noted above, during  1995, Chiron's Compensation  Committee consisted of
Drs. Amelio, Strijkert, Krauer and Schramek and Mr. Coleman.
 
    Under the  Governance Agreement,  subject to  certain conditions,  Ciba  has
agreed  to  nominate (and,  at the  end  of each  term, renominate)  Dr. Rutter,
Chairman of the Company, for election  to Ciba's Board of Directors. Dr.  Krauer
has  been the Chairman  of the Board  and Chief Executive  Officer of Ciba since
1987. Under the  terms of  the Governance Agreement,  Dr. Krauer  is serving  on
Chiron's   Compensation  Committee  as  a  designee  of  Ciba.  See  "Ciba-Geigy
Transaction" above at  p. 2  and "Related  Transactions" below  at p.  20 for  a
further description of Chiron's relationships with Ciba.
 
           COMPENSATION COMMITTEE REPORT ON EXECUTIVE COMPENSATION(1)
 
    Decisions  on compensation of  the Company's executive  officers are made by
the Compensation  Committee  of the  Board  of  Directors. All  members  of  the
Compensation  Committee during 1995 were  non-employee directors. As required by
the rules of the Securities and Exchange Commission, this Compensation Committee
Report describes the matters considered generally by the Compensation  Committee
in  reaching  its  decisions  regarding  compensation  for  executive  officers,
including Dr.  Edward  Penhoet, Chief  Executive  Officer; Dr.  William  Rutter,
Chairman; and Messrs. William Green, Dennis Winger, and C. William Zadel(2), the
executive  officers,  who  together  with  Drs.  Rutter  and  Penhoet,  were the
Company's five most highly compensated executives for 1995.
 
COMPENSATION PHILOSOPHY
 
    Chiron's executive compensation  programs seek to  accomplish several  major
goals:
 
        - To align the interests of executive officers with the long-term
          interests   of  stockholders   through  participation   in  the
          Company's stock option plan;
 
        - To  motivate  executives  to  achieve  important  business  and
          individual  performance objectives and to reward them when such
          objectives are met; and
 
        - To recruit and  retain highly qualified  executive officers  by
          offering  overall  compensation that  is competitive  with that
          offered for comparable positions  in other biotechnology,  high
          technology and pharmaceutical companies.
 
    The  Compensation  Committee administers  executive compensation  to support
Chiron's business mission of  becoming a leading biotechnology-based  healthcare
company.  For 1995,  the Company's  compensation program  included the following
components: (i) a base  annual salary; (ii)  annual variable cash  compensation,
which  was provided under the 1995  Executive Officer Variable Cash Compensation
Plan (the "1995 Plan")  as to those  officers subject to  Section 162(m) of  the
Internal  Revenue Code  (which includes  all of  the Senior  Executives)(3); and
(iii) long-term equity-based incentives in the form of stock options.
 
- ------------------------
(1) The  material in  this report  and  under the  caption "Common  Stock  Price
    Performance  Graph" are not "soliciting material," are not deemed filed with
    the Securities and  Exchange Commission and  are not to  be incorporated  by
    reference  in any filing of the Company under the Securities Act of 1933, as
    amended, or the Exchange Act whether made  before or after the date of  this
    Proxy  Statement  and  irrespective of  any  general  incorporation language
    therein.
 
(2) Mr. Zadel was the President of CCD until his resignation effective  December
    31,  1995. His compensation for 1995  was determined exclusively by: (i) the
    terms of his employment  when CCD was acquired  by the Company effective  on
    January  1,  1995  and (ii)  the  terms  of an  agreement  with  the Company
    regarding  his  severance   discussed  below   at  p.   25  under   "Related
    Transactions".
 
(3)  The term Senior Executives means Drs.  Rutter and Penhoet and Messrs. Green
    and Winger. The Senior  Executives, together with Mr.  Zadel, were the  five
    most highly compensated executives of the Company for 1995.
 
                                       14
<PAGE>
COMPENSATION COMMITTEE PROCEDURES AND PERFORMANCE CONSIDERATIONS REGARDING 1995
EXECUTIVE COMPENSATION
 
    In  February of each year, the  Compensation Committee meets to consider the
Company's performance  and the  performance of  each executive  officer for  the
prior  year. For 1995,  this meeting occurred  on February 22  and 23, 1996. The
Committee reviewed the performance of the  Company, its business units, and  the
executive  officers, other than the Senior  Executives, and approved base salary
recommendations for 1996 and variable cash compensation for performance in  1995
for each of them at its meeting on February 22, 1996. The Committee sought input
from  Drs. Penhoet and Rutter,  the Chief Executive Officer  and Chairman of the
Board, regarding the performance of all other executive officers. The  Committee
solicited  the views of seven other  executive officers of the Company regarding
the performances of  Drs. Rutter and  Penhoet. The Committee  also met with  the
remaining  non-employee directors to  consider further the  performances of Drs.
Rutter and Penhoet. The Committee approved the base salary for 1996 for each  of
the Senior Executives on February 23, 1996. It also certified the accomplishment
of  the performance objective  under the 1995  Plan -- an  increase over 1994 of
greater than 20  percent in  operating earnings  before taxes,  as adjusted  for
certain extraordinary items. The Committee exercised its discretion as permitted
by  that  plan  to  reduce  the  variable  compensation  awards  for  the Senior
Executives to  the levels  shown in  the Summary  Compensation table  at p.  11.
Similar  meetings occurred in February 1995 to review performance of the Company
and executive officers in  1994 and to determine  each executive officer's  base
salary for 1995.
 
    The  Compensation Committee concluded that the Company's overall performance
in 1995 justified favorable consideration  of all executive officers,  including
the  Senior Executives, for increases in base  salary for 1996, for stock option
awards and, subject to the  1995 Plan as applied  to the Senior Executives,  for
awards  of variable cash compensation. The Committee noted the overall financial
and operational performance of the Company in 1995 and its success in  effecting
the  fundamental repositioning of each of its business units for sustainable and
profitable growth and  to play  important strategic  roles in  the markets  each
serves.  The  Committee  specifically  considered the  following:  In  1995, the
Company  more  than  doubled  in  employees  and  sales.  The  acquisition   and
integration  of CCD into Chiron Diagnostics was accomplished while expanding the
sales and profit  contribution of  the diagnostics business  at rates  exceeding
those of the diagnostics industry as a whole. The acquisition and integration of
IOLAB  into  Chiron Vision  nearly  doubled the  revenues  of Chiron  Vision and
positioned its cataract business strongly among  the top three companies in  the
market.   The  acquisition  and   integration  of  Viagene,   Inc.  into  Chiron
Technologies strengthened  the  Company's  position in  a  fundamental  enabling
technology  for  pharmaceutical  development.  In  1995,  Chiron  developed  and
initiated implementation of strategic initiatives in each of its business  units
to  continue and accelerate its transformation into a leading healthcare company
based on biotechnology.
 
    Based on the favorable determination  of Company performance, the  principle
factors  which  were  used  to fix  each  executive  officer's  salary increase,
variable cash compensation  award, and  stock option award  were the  subjective
evaluation  of the individual's performance and, where relevant, the performance
of the officer's business unit or  functional area of responsibility and  survey
information  concerning  corresponding  elements of  compensation  for benchmark
positions from a survey group of  comparable companies. Officers subject to  the
1995  Plan were entitled to variable cash compensation determined as a result of
achievement of the performance objective  established under that plan for  1995.
The  stock option grants to  the Senior Executives in 1995  are set forth in the
option grant  table on  p. 12.  In determining  the size  of these  grants,  the
Committee  did  not consider  the number  of  stock options  previously awarded,
whether vested or unvested, or the aggregate number of outstanding stock options
held by the recipients of the current awards.
 
SURVEY COMPARISONS FOR 1995
 
    The Committee continued for  1995 the Company's  general approach that  base
salaries  for  executive  officers  should  be  compared  to  the  median  (50th
percentile) of base  salaries for benchmark  positions in comparable  companies.
Further,  the Compensation Committee intends that a significant portion of total
cash compensation (salary plus variable compensation) should be in the form of a
variable annual cash award that is "at risk", dependent on individual,  business
unit and overall Company performance.
 
                                       15
<PAGE>
    The  Company has retained  Hewitt & Associates,  an independent compensation
consulting firm ("Hewitt"),  to evaluate  the appropriateness  of the  Company's
executive  compensation  programs.  That  firm  has  provided  the  Compensation
Committee with survey data using analyses of benchmark positions from a group of
selected biotechnology,  high  technology  and pharmaceutical  companies  (  the
"Survey Group") with whom the Company competes for the recruitment and retention
of  executive personnel. Median annual  sales for 1995 of  the Survey Group as a
whole were $3.4  billion. The common  stock performance graphs  on pp. 19-20  of
this  proxy  statement  provide  stock  performance  information  for  groups of
companies that  include some,  but not  all, of  the companies  included in  the
Survey Group.
 
    The survey information serves as a general reference for the Company and the
Compensation  Committee. However, because of many other factors, including those
described above and the  inherent lack of  comparability between any  individual
officer's  responsibilities,  performance,  and  value to  the  Company  and the
average information from the Survey Group, no element of any executive officer's
compensation is  determined solely  or principally  by reference  to the  survey
information.  The  survey  information  concerning  base  salaries  of benchmark
positions shows  that  the  Company's overall  salary  structure  for  executive
officers  is slightly above the  50th percentile level of  the Survey Group on a
size-adjusted basis and  below the  50th percentile of  the Survey  Group on  an
unadjusted  basis.  The  survey information  regarding  total  cash compensation
indicates that executive officers' total cash compensation (salary and  variable
compensation) in the aggregate is in the third quartile of the Survey Group on a
size-adjusted  basis  and at  or slightly  below the  median for  most benchmark
positions of the Survey Group on an unadjusted basis.
 
LONG TERM INCENTIVES -- STOCK OPTIONS AND PERFORMANCE UNITS
 
    The Compensation  Committee  believes that  stock  option awards  under  the
Company's  1991 Stock Option Plan serve to  align the long-term interests of the
Company's executive  officers  with those  of  its stockholders  and  contribute
importantly  to the recruitment and retention  of executive personnel. Under the
1991 Stock Option Plan, the Company's executive officers are eligible to receive
grants of options  to purchase shares  of the Company's  stock. The options  are
generally  granted upon initial employment and annually thereafter with exercise
prices generally  equal  to  the  prevailing market  price  at  date  of  grant.
Therefore,  stock options will  have value to  the executive only  to the extent
that the market  price for the  Company's stock increases.  Stock option  grants
generally  become exercisable  or "vest" in  increments over four  (4) years, so
long as service of the option recipient with the Company continues.
 
    Executive officers,  including the  Senior  Executives, received  two  stock
option  awards in  1995. The  first of  these were  annual awards,  as described
above, in which  vesting occurs over  four years of  continued service with  the
Company.  The  second award,  in May  1995,  represented a  first step  to align
long-term, equity-based incentive compensation with performance objectives.  The
Senior  Executives  and  other  senior  managers  within  the  Company  received
"performance-accelerated" stock  options  for which  vesting  will occur  as  to
one-third  of the shares subject to each such option at the end of each calendar
year commencing with 1996 in which the Company meets or exceeds the "Measurement
Standards". The  Measurement  Standards  are a  set  of  performance  objectives
determined  annually  by the  Board of  Directors  to satisfy  the terms  of the
Governance Agreement between Chiron and  Ciba. If the Measurement Standards  are
not  met in  any year, the  option vesting  is not accelerated,  but the options
remain outstanding and unvested, to become exercisable only upon achievement  of
the Measurement Standards in a future year, or after May 2001, for those options
held by recipients then still employed by the Company.
 
    As described in this proxy statement under Proposal 3, to strengthen further
the  link  between  compensation  and  performance  objectives,  the  Company is
amending its  1991 Stock  Option Plan  to provide  for the  award of  restricted
shares,  share rights  and share units  which become  vested ONLY if  and to the
extent that specific performance objectives are achieved ("performance  units").
The  Compensation  Committee, based  on Hewitt's  analysis, expects  that annual
stock option grants will provide long-term incentive compensation for  executive
officers,  including the Senior Executives, at approximately the 50th percentile
level of the Survey  Group and that achievement  of higher compensation  through
equity-based  incentives up  to approximately the  75th percentile  level of the
Survey Group  will  depend  upon  achievement  of  performance  objectives.  The
Committee  has awarded performance units in 1996  which will vest, if at all, in
1999 based
 
                                       16
<PAGE>
upon the three-year relative total  shareholder return, as measured by  dividend
yield and cumulative stock price appreciation of Chiron Common Stock as compared
to  two stock market indices -- The  AMEX Biotechnology Index and the Standard &
Poor's Health Care Composite Index.
 
CHIEF EXECUTIVE OFFICER COMPENSATION
 
    Dr. Penhoet has the title President  and Chief Executive Officer of  Chiron.
Many  senior  managerial  responsibilities,  however,  are  shared  between Drs.
Penhoet and Rutter. Effective February  1, 1995, the Compensation Committee  had
established base salaries of $400,000 for each of them, representing an increase
of  approximately 6.7  percent from  1994. On  February 23,  1996, the Committee
approved a variable cash compensation award under the 1995 Plan for fiscal  year
1995  for Drs. Penhoet and Rutter of  $350,000 each, based on the achievement in
1995 as  certified by  the Committee  of the  1995 performance  objective --  an
increase  over  1994 of  greater than  20 percent  in operating  earnings before
taxes, as adjusted for certain extraordinary items. The Committee fixed the base
salary and exercised  its permitted  discretion under the  1995 Plan  as to  Dr.
Penhoet  after considering:  his contribution to  building long-term stockholder
value through employee development,  external relations and skillful  management
of corporate interactions, and his ability to work effectively with external and
internal  constituencies and collaborators. The  Committee fixed the base salary
and exercised  its  discretion  under the  1995  Plan  as to  Dr.  Rutter  after
considering:  his overall leadership,  the contribution of  his strategic vision
and the dramatic transformation of  the Company's business units and  strategies
in  1995. The Committee  also considered corresponding  elements of compensation
for comparable positions from the Survey  Group. The base salary and total  cash
compensation  of each  of Drs. Rutter  and Penhoet  are below the  median of the
Survey Group on an absolute and a size-adjusted basis.
 
    As described above, the Compensation Committee granted stock options to Drs.
Rutter and Penhoet, and the other Senior  Executives in 1995 in the amounts  set
out  in the option grant table  on p. 12. The awards  to Drs. Penhoet and Rutter
were based on,  among other  things, subjective assessment  of their  respective
past contributions, and anticipated future contributions to the Company.
 
    As  shown in the option exercise table on p. 13 above, Dr. Penhoet exercised
stock options during 1995 that were granted  to him in 1987 and which expire  in
1997. The options had an exercise price per share equal to the market price of a
share  of the Company's Common  Stock on the date  the options were granted, and
became exercisable  or  "vested"  in increments  with  Dr.  Penhoet's  continued
employment  with  the  Company.  The amounts  realized  by  Dr.  Penhoet through
exercise of  these  stock  options  resulted solely  from  appreciation  of  the
Company's  stock  price during  his  tenure as  Chief  Executive Officer  of the
Company. Dr.  Rutter exercised  no  stock options  in  1995. During  1995,  Drs.
Penhoet  and Rutter also exercised the right granted to Chiron option holders at
November 20,  1994 by  Ciba  to surrender  certain  eligible stock  options  for
cancellation  in consideration of a cash payment  from Ciba of $117 a share less
the exercise price. Compensation received as  a result of such option  surrender
is described in footnote 1 to the option exercise table on p. 13.
 
POLICY REGARDING SECTION 162(m)
 
Section  162(m) limits  federal income tax  deductions for  compensation paid to
each of the chief executive officer  and the four other most highly  compensated
officers  of a public company to $1,000,000  per year, but contains an exception
for certain performance-based compensation.  The Compensation Committee  expects
to  continue to use the  1995 Plan, stock options  and performance units awarded
under  the  amendments  to  the  1991  Stock  Option  Plan  being  proposed  for
consideration  by  the stockholders  at  the 1996  Annual  Meeting, in  order to
preserve federal  income  tax deductions  that  might otherwise  be  limited  by
Section  162(m), so long as  the Committee considers such use  to be in the best
interest of the Company and its stockholders.
 
    The Compensation  Committee, nevertheless,  may award  stock options,  other
equity-based   compensation  or  variable  cash   compensation  under  plans  or
procedures that are not intended to qualify for exemption to the Section  162(m)
limitations.  As  described above  under Long-Term  Incentives, the  Company has
developed programs  to link  long-term, equity-based  incentive compensation  to
performance  objectives. The Compensation Committee  has approved in concept the
implementation in 1996 and 1997 of global strategic
 
                                       17
<PAGE>
approaches to compensation in which: (i)  a portion of each executive  officer's
long-term,  equity-based incentives  will be in  the form  of performance units,
subject to stockholder approval of amendments  to the 1991 Stock Option Plan  as
described  in Proposal  3 of  this proxy  statement, and  (ii) executive officer
annual variable  cash compensation  will  be linked  to achievement  of  annual,
quantifiable  "success metrics" that grow from  the Company's strategic plan and
are implemented through annually updated operating plans of the Company and each
of its business units.  The Compensation Committee elected  not to grant  awards
under  the  1995  Plan  for  1996,  because  it  felt  that  the  variable  cash
compensation  for  1996  of  all  executive  officers  should  be   administered
consistently,  using the Company's "success  metrics" as performance objectives.
The success  metrics  contain  performance milestones  that  are  insufficiently
objective  to  satisfy  Section  162(m). Accordingly,  to  the  extent  that the
variable cash compensation for 1996 of  any of the five most highly  compensated
officers,  together  with  other  compensation that  does  not  qualify  for the
performance-based exceptions, exceeds $1,000,000 in 1997, the Company will  lose
a  tax deduction.  It is  not expected  that the  compensation of  any executive
officers will exceed $1,000,000 in 1997, unless an officer elects to receive all
or a portion of the cash payments that may be made by Ciba to certain holders of
Chiron stock options, which payments are not exempt from the application of  the
Section 162(m) limitations.
 
                                          COMPENSATION COMMITTEE
 
                                          Lewis W. Coleman, ACTING CHAIRMAN
                                          Alex Krauer
                                          Henri Schramek
                                          Pieter J. Strijkert
 
                                       18
<PAGE>
                      COMMON STOCK PRICE PERFORMANCE GRAPH
 
    The  first graph below  compares cumulative total  stockholder return on the
Common Stock of  Chiron for the  five years  ended December 31,  1995, with  the
cumulative  total return on the NASDAQ Global Stock Index, the Hambrecht & Quist
Health Care Stock  Index, and the  NASDAQ Pharmaceuticals Stock  Index over  the
same period.
 
    The  second graph compares cumulative total stockholder return on the Common
Stock of Chiron for the five years ended December 31, 1995, with the  cumulative
total  return on the Standard & Poor's  Health Care Composite Index and the AMEX
Biotechnology Index over the same period. The Compensation Committee has adopted
these indices for use in measuring  corporate performance as discussed above  in
the  Compensation  Committee  Report  on Executive  Compensation  at  pp. 16-17.
Subject to stockholder approval of the  Amended 1991 Stock Option Plan which  is
the  subject of Proposal  3 in this proxy  statement, the Compensation Committee
has awarded performance units in 1996 which will vest, if at all, in 1999, based
upon the 3-year relative total shareholder return, as measured by dividend yield
and cumulative stock price  appreciation of Chiron Common  Stock as compared  to
the  Standard &  Poor's Health Care  Composite Index and  the AMEX Biotechnology
Index. For  these  reasons,  the  Company has  elected  to  provide  information
comparing the Company's total return with the newly selected indices in addition
to the indices used last year.
 
    The  graphs assume $100 were  invested on December 31,  1990, in Chiron, and
each of the indices, and that dividends were reinvested. The comparisons in  the
graphs  are  required by  the  Securities and  Exchange  Commission and  are not
intended to forecast  or be  indicative of  possible future  performance of  the
Company's Common Stock.
 
EDGAR REPRESENTATION OF DATA POINTS USED IN PRINTED GRAPHIC
 
<TABLE>
<CAPTION>
           CHIRON STOCK    NASDAQ - GLOBAL STOCK INDEX    NASDAQ PHARMACEUTICALS STOCK INDEX    H&Q HEALTH CARE STOCK INDEX
<S>        <C>            <C>                            <C>                                   <C>
1990                 100                            100                                   100                            100
1991                 159                            160                                   266                            243
1992                 128                            185                                   221                            208
1993                 191                            214                                   197                            162
1994                 183                            207                                   148                            163
1995                 251                            288                                   271                            274
</TABLE>
 
                                       19
<PAGE>
EDGAR REPRESENTATION OF DATA POINTS USED IN PRINTED GRAPHIC
 
<TABLE>
<CAPTION>
           CHIRON STOCK   S&P HEALTHCARE INDEX    AMEX BIOTECH INDEX
<S>        <C>            <C>                    <C>
1990                 100                    100                   100
1991                 159                    151                   291
1992                 128                    123                   233
1993                 191                    109                   158
1994                 183                    120                   112
1995                 251                    185                   182
</TABLE>
 
                              RELATED TRANSACTIONS
 
    From  April 1987 through December 31, 1994,  Chiron and an affiliate of Ciba
each owned a 50 percent equity interest in The Biocine Company, a joint  venture
partnership  formed for vaccine research. In  1992, Chiron and Ciba acquired the
vaccine business of  Sclavo S.p.A. of  Siena, Italy, and  renamed this  business
Biocine  S.p.A. Through December 31, 1994, Chiron and Ciba each owned 50 percent
of Biocine S.p.A and  shared equally in its  management, profits and losses  and
capital funding requirements.
 
    In  November 1994,  Chiron and  Ciba entered  into the  Investment Agreement
which provided  for the  creation of  a strategic  partnership between  the  two
companies  and  a partial  tender  offer by  Ciba  to purchase  approximately 38
percent of the Company's outstanding Common Stock and the sale by Ciba to Chiron
of its interests in The Biocine Company and Biocine S.p.A as well as all of  the
issued  and  outstanding shares  of CCD  ("the Ciba  Biocine Business"  and "CCD
Shares"), in consideration  for which Chiron  sold to Ciba  6,600,000 shares  of
Chiron  Common Stock and made a cash payment to Ciba of $24 million. The sale to
Chiron of  the Ciba  Biocine Business  and CCD  Shares was  completed  effective
January 1, 1995 (the "Closing").
 
    The  Investment Agreement provides that after  the Closing, Ciba shall issue
to a  bank  selected by  Ciba  and reasonably  acceptable  to the  Company  (the
"Selected  Bank")  a  guarantee  for  the  benefit  of  the  Company  (the "Ciba
Guarantee") pursuant to which Ciba will guarantee for the benefit of the Company
a credit facility  provided by the  Selected Bank. The  principal amount of  the
Credit  Facility  that may  be  outstanding at  any  time is  $425  million (the
"Maximum Borrowing Amount"), except that  the Maximum Borrowing Amount shall  be
reduced by $1.50 for each $1.00 in additional funding (up to $50 million in such
additional funding) requested by the Company under the Limited Liability Company
Agreement described below. The Company shall repay any outstanding amounts under
the  Credit Facility  to the  extent such  amounts exceed  the Maximum Borrowing
Amount. The Company  may not  borrow or reborrow  any amounts  under the  Credit
Facility  after the fifth anniversary of the Closing unless Ciba and the Company
otherwise agree.
 
    The Investment  Agreement  provides  further that  simultaneously  with  the
issuance  of  the  Ciba  Guarantee,  the Company  shall  execute  and  deliver a
reimbursement agreement (the "Reimbursement Agreement")
 
                                       20
<PAGE>
pursuant to which the Company will agree to reimburse Ciba for any payments made
by Ciba pursuant to the Ciba  Guarantee as well as all reasonable  out-of-pocket
costs  and expenses incurred by Ciba in  connection with the Ciba Guarantee. The
Company's  obligations  under   the  Reimbursement  Agreement   will  be   fully
collateralized  by any collateral,  including equity securities  of the Company,
that is reasonably  acceptable to  Ciba. The Reimbursement  Agreement also  will
contain a negative pledge covenant with respect to the collateral and such other
terms  and conditions as are customary  to reimbursement agreements of its type.
Pursuant to  the above-described  terms, in  1995, Ciba  guaranteed a  revolving
credit  facility for the benefit of the Company in the amount of $50 million and
the Company executed a reimbursement agreement as to such amount.
 
    In connection with  the acquisition  of CCD by  the Company  from Ciba,  all
existing  indebtedness of CCD and its subsidiaries to Ciba was consolidated into
a single loan from Ciba to CCD evidenced  by a promissory note in the amount  of
$50,760,000,  maturing  January  1,  2000. At  December  31,  1995,  interest of
$3,255,777, at a  variable rate  based on LIBOR,  had accrued  on the  principal
amount  outstanding  under  that  promissory  note.  In  addition,  certain Ciba
subsidiaries engaged in the business of commercial finance make lines of  credit
available  to certain overseas subsidiaries of the Company. Accrued interest and
fees payable to Ciba by the Company under such credit facilities in 1995 totaled
$303,000. The interest rate  and charges on both  the note and these  facilities
are  more favorable to the Company than  would be the terms reasonably available
to the Company  under comparable financing  from any unaffiliated  institutional
lender.
 
    To  implement  the research  funding commitment  by  Ciba in  the Investment
Agreement, during 1995, Ciba  and the Company entered  into a Limited  Liability
Company  Agreement, under which  Ciba will purchase interests  in a newly formed
Limited Liability  Company (the  "LLC") as  a means  of providing  funding.  The
Agreement  contains the  following terms:  (i) during  the period  commencing on
December 28, 1995, and ending on December 31, 1999 (the "Funding Period"),  Ciba
will  fund, at Chiron's  request, research and  development expenses incurred by
the Company on or after January  1, 1995, for certain Funded Projects  currently
under  development which initially consist of adult vaccines, pediatric vaccines
and Insulin-like growth factor-I;  (ii) during the  Funding Period, the  Company
shall  be entitled to propose additional Funded Projects from time to time which
the Company  wishes  Ciba  to fund  or  partially  fund; (iii)  subject  to  the
limitations  set forth below, Ciba will fund  its share of all development costs
of Funded Projects, which  shall be 100  percent, or such  lesser amount as  the
parties  may agree (but not in excess of the maximum funding provided for in the
Investment Agreement); (iv) the obligation of Ciba to fund Funded Projects shall
be subject to the following limitations: (a) in no event shall Ciba be obligated
to provide funding to the Company in any calendar year during the Funding Period
for Funded Projects in an amount in excess of (x) $34,000,000 in 1995, (y)  $123
million  in 1996 and (z) for calendar years thereafter, equal annual portions of
the remaining unexpended aggregate amount under  (b) below; and (b) in no  event
shall  (x) the aggregate amount of funding  provided to the Company by Ciba LESS
(y) the aggregate amount of any payments to or profits paid or earned by Ciba in
connection with any product or products developed in any Funded Projects at  any
time during the Funding Period exceed $250,000,000; provided, however, that such
amount  may be  increased, at  the Company's request,  to up  to $300,000,000 in
consideration of a reduction in the Maximum Borrowing Amount (as defined  above)
at  the rate  of $1.00  of increased research  and development  funding for each
$1.50 reduction of  the Credit  Facility; (v)  in consideration  of the  funding
provided  by Ciba for the Funded Projects,  and subject to the Company's buy-out
right  described  below,  but   without  thereby  guaranteeing  the   successful
conclusion  of any project  included in the Funded  Projects, Ciba will receive,
through its interest in the LLC, an  interest in a stream of variable  royalties
in  future worldwide sales  from certain adult  vaccines, pediatric vaccines and
Insulin-like growth factor  I (the  "Products") and an  interest in  promotional
rights,  in countries other than in North  America and Europe, for certain adult
vaccines; (vi) in  the event that  the Company requests  funding for  additional
Funded Projects in the future, the Company will offer Ciba, through its interest
in  the LLC, the opportunity to share in additional product opportunities, which
may be in the form of royalties, profit sharing or participation in distribution
or sales activities in selected geographic  markets or otherwise; and (vii)  the
Company shall have the right, but not the obligation, to buy out Ciba's interest
in  the  LLC (including  Ciba's interest  in  royalties, co-promotion  and other
product rights) upon tender by the Company  to Ciba of payment in the amount  of
the  Buyout Amount (as described below) provided that such right shall expire if
such tender is not made prior to January 1, 2002.
 
                                       21
<PAGE>
The "Buyout Amount" means, as of the time of tender the amount equal to (i)  the
sum of all payments made by Ciba to the Company to purchase interests in the LLC
prior  to such time, PLUS (ii) interest on such amount at LIBOR from the date of
payment to the date of tender, LESS  (iii) the aggregate amount of all  payments
or  profits received by Ciba  in distributions from the  LLC and in co-promotion
profits, LESS (iv)  interest on  the amount referenced  in (iii)  at LIBOR.  The
Company  shall be entitled to make the payment  of the Buyout Amount in the form
of cash or Common Stock, or a combination of the two. In the event of a  buyout,
Ciba  retains certain distribution  rights with respect to  adult vaccines as to
which it has then exercised its promotion rights. Under the terms of the Limited
Liability Company Agreement, the  Company received $27  million of funding  from
Ciba  during 1995.  Chiron anticipates receiving  substantial additional funding
from Ciba in future periods, pursuant to the terms of the Agreement.
 
    Ciba  and  the  Company   have  also  entered   into  the  Cooperation   and
Collaboration  Agreement  regarding  research  and  development  collaborations,
marketing and  manufacturing arrangements,  access of  each party  to the  other
party's  technology and reciprocal most  favored nation rights regarding certain
licenses. The agreement  provides a  mechanism by  which either  party may  make
specific  proposals for areas of research and development collaboration with the
other and retain a 90-day right of first negotiation with respect to such areas.
Neither party  to  such agreement  has  the right  to  enter into  any  material
research  and  development  collaboration  related  to  the  Company's strategic
mission with any third party if such third party's only material contribution to
the collaboration is expected to be funding, unless such party has first offered
the other party  the opportunity to  enter into such  collaboration on the  same
terms  as such third party,  provided that such restrictions  shall not apply to
collaborations with non-commercial sources of  funding, including grants, or  to
financing  arrangements with  third parties  in which  the consideration  to the
third party is the return on  financing. In addition, under the Cooperation  and
Collaboration  Agreement,  the  parties have  (x)  a reciprocal  right  of first
refusal with respect to marketing certain products developed by the other  party
or  with respect  to which the  other party  has the right  to market  and (y) a
reciprocal right  of first  negotiation with  respect to  manufacturing  certain
products  developed by the other party or  with respect to which the other party
has the right to manufacture.
 
    The first collaboration  project between the  Company and Ciba  contemplated
under   the  Cooperation  and  Collaboration  Agreement   is  in  the  field  of
combinatorial chemistry. In November 1995, the  Company and Ciba entered into  a
collaboration  agreement under which Ciba will pay $26.0 million to Chiron, over
a five-year  period  and subject  to  certain  adjustments, in  exchange  for  a
non-exclusive,  perpetual  license to  utilize Chiron's  combinatorial chemistry
techniques. In addition, the parties  will collaborate to utilize  combinational
chemistry  technology to identify  potential products in  selected target areas.
The agreement  provides  for research  funding  by Ciba,  and  certain  upfront,
milestone  and royalty payments, as well as product commercialization rights for
both parties. In the fourth quarter of 1995, Chiron received a payment from Ciba
of $5.5 million under the terms of the agreement.
 
    Under the Governance Agreement, so long  as Ciba has the right to  designate
for nomination at least one Investor Director, subject to certain exceptions, if
the  Board of Directors  authorizes the issuance of  any Equity Securities after
the Closing, Ciba will  have the right  to purchase its Pro  Rata Share of  such
securities.  As used herein,  "Pro Rata Share"  means the fraction  of an entire
issuance of securities, the numerator of which shall be the number of shares  of
Common  Stock owned by Ciba  and its affiliates (other  than the Company and its
subsidiaries) immediately  prior to  such issuance  of such  securities and  the
denominator  of which shall  be the aggregate  number of shares  of Common Stock
outstanding immediately prior to such issuance of such securities. If Ciba shall
elect to purchase any such securities,  such securities will be issued and  sold
to  Ciba by the Company at the same time and on the same terms and conditions as
the new securities are issued  and sold to third  parties (except that, if  such
securities are issued for consideration other than cash, Ciba shall pay the fair
market   value  thereof,  as  determined   in  accordance  with  the  Governance
Agreement).
 
    Ciba and  the  Company  have  also entered  into  the  Market  Price  Option
Agreement  pursuant  to  which Ciba  shall  have  the right  to  purchase shares
directly from the Company under  the circumstances described below. Pursuant  to
the  Market  Price  Option  Agreement,  the  Company  granted  to  Ciba  Biotech
Partnership, Inc., an affiliate of  Ciba ("Ciba Biotech") an irrevocable  option
(the "Option") to purchase on each
 
                                       22
<PAGE>
exercise  closing date,  on the  terms and subject  to the  conditions set forth
therein, up to the number of newly-issued shares (the "Option Shares") equal, as
of the related Exercise Date  (as defined below), to  the number of Shares  that
Ciba  would be permitted to  purchase from persons other  than the Company as of
such Exercise Date under the Governance Agreement.
 
    The Market Price Option Agreement provides that the Option may be  exercised
by  Ciba Biotech (or  its designee, which designee  must be Ciba  or a direct or
indirect wholly-owned subsidiary of Ciba), in whole or in part, at any time,  or
from  time  to time  (the date  of any  such  exercise being  referred to  as an
"Exercise Date"), during the period beginning upon the Closing and ending on the
date  that  Ciba  and  its  affiliates  become  the  beneficial  owners  of  all
outstanding  shares of Equity  Securities, so long as  an Exercise Condition (as
defined below) shall exist on such  Exercise Date; provided, however, that  Ciba
Biotech may not exercise the Option at any time unless it owns Equity Securities
representing at least 30 percent of the aggregate number of votes entitled to be
voted  in an election of directors of  the Company by all the outstanding voting
stock. The  Option  may  be  repeatedly exercised  by  Ciba  Biotech;  provided,
however,  that each exercise of the Option  for fewer than the maximum number of
Shares then issuable pursuant to an exercise of the Option shall be for at least
that number of shares that results in a purchase price of $1,000,000.
 
    Pursuant to the Market Price Option Agreement, an "Exercise Condition" shall
exist if  any  of the  following  conditions  are satisfied:  (i)  Ciba  Biotech
concludes  that  it  is  in  any  way legally  (including  as  a  result  of any
regulation)  restricted  from  purchasing  or  otherwise  acquiring  any  Equity
Securities  from any  person other than  the Company,  including any restriction
resulting from Ciba Biotech's possession of any non-public material  information
regarding  the Company; (ii)  Ciba Biotech concludes  that there is insufficient
liquidity in the open market to permit it to (A) purchase on the open market the
amount of Equity Securities it desires to purchase within the time period during
which it desires to make such purchases  or (B) make such purchases within  such
time  period without such  purchases unduly affecting  the price of  any of such
Equity Securities, in which case  the Option may be  exercised to the extent  of
such  insufficient  liquidity as  determined by  Ciba  Biotech, or  (iii) Ciba's
Percentage Interest  is  below 50  percent  and  Ciba Biotech  desires,  and  is
permitted under the Governance Agreement, to increase Ciba's Percentage Interest
to  a percentage exceeding 50 percent; provided  that if as of any Exercise Date
the only existing Exercise Condition is the condition specified in clause  (iii)
above,  then Ciba Biotech shall not purchase  through the exercise of the Option
on such  date any  Shares  that would  increase  Ciba's Percentage  Interest  to
greater than 51 percent. The purchase price for any Shares purchased pursuant to
an exercise of the Option shall be the Fair Market Value of such shares.
 
    Ciba  and  the Company  have also  entered  into the  Subscription Agreement
pursuant to which the Company shall have the right, exercisable at any time  and
from  time  to time  during the  eleven  year period  following the  Closing, to
require Ciba Biotech to  acquire Common Stock of  the Company directly from  the
Company  at Fair Market Value (as defined  below) up to the Subscription Amount.
"Subscription Amount" means, initially $500,000,000, and thereafter, such amount
as reduced by the aggregate  price paid from time to  time after the Closing  by
Ciba  Biotech or any of  its affiliates to the Company  or any subsidiary of the
Company for each purchase from the Company  or any subsidiary of the Company  of
any  Equity Securities of  the Company by  any of them,  whether pursuant to the
Market Price  Option  Agreement,  the  Governance  Agreement,  the  Subscription
Agreement  or  otherwise  except  for  (i)  purchases  by  Ciba  Biotech  or its
affiliates in connection with collaborations entered into by Ciba Biotech or its
affiliates and the Company in accordance  with the terms of the Cooperation  and
Collaboration  Agreement  or  (ii)  Equity  Securities  issued  to  Ciba  or its
affiliates in  accordance  with  the  terms of  the  Limited  Liability  Company
Agreement.  Ciba Biotech's  obligation to  purchase any  shares pursuant  to the
Subscription Agreement will be subject to the satisfaction as of the  applicable
closing date of certain conditions.
 
    Except  as described in the second paragraph of "Related Transactions" above
at p. 20, in  fiscal year 1995,  Ciba did not purchase  any securities from  the
Company pursuant to the Market Price Option Agreement, the Governance Agreement,
the Subscription Agreement or otherwise.
 
    The  Governance Agreement provides that the  Company will not enter into any
material transaction with Ciba or any of its affiliates after the Closing (other
than those expressly contemplated by the Investment
 
                                       23
<PAGE>
Agreement, the Governance Agreement or  any other Ancillary Agreement) unless  a
majority  of the Independent  Directors or holders  of a majority  of the voting
power of the  voting stock which  is held by  unaffiliated stockholders  approve
such transaction.
 
    The  Company and subsidiaries  received revenue of  $10,348,800 in 1995 from
sales of products  and services  to Ciba,  including revenue  of $6,721,800  for
promotional  services provided  in connection  with the  sale of  Ciba's product
Aredia-Registered Trademark-.
 
    In connection with  the acquisition of  CCD from Ciba  by the Company,  Ciba
agreed  that Ciba and its subsidiaries would continue for a reasonable period to
provide to  CCD and  its subsidiaries  administrative and  similar services  and
incidental  research and development services. Such  services are required to be
provided at Ciba's cost. Use of Ciba  services has been expanded where Ciba  has
been  determined to  be the  best available source  for a  particular service or
phased out where  more attractive alternative  sources for a  service have  been
identified.  In  1995,  the  Company  paid  Ciba  $195,000  for  purchasing  and
distribution support, $832,000  for overseas office  support, $640,000 for  data
processing,   telecommunications  and  information  services  and  $550,000  for
research and development services. For 1996, budgeted payments to Ciba for these
services are  approximately $196,000  for purchasing  and distribution  support,
$738,000   for   overseas  office   support,   $872,000  for   data  processing,
telecommunications and  information  services  and  $165,000  for  research  and
development services.
 
    In  fiscal year 1995, Biocine S.p.A.,  a subsidiary of the Company, incurred
approximately $662,000 of commissions  on the sale of  vaccines by Ciba and  its
affiliates.  In  addition,  Biocine  S.p.A.  earned  approximately  $507,000  in
interest income during fiscal  year 1995 from an  interest-bearing deposit in  a
financing subsidiary of Ciba.
 
    Under  the  terms of  the Investment  Agreement, all  holders of  options to
acquire shares of Common Stock under Chiron's 1991 Stock Option Plan on November
20, 1994,  including  executive officers  and  directors of  the  Company,  were
granted  certain cash  payment rights in  connection with  the Ciba transaction.
Each optionee was granted  the right to  receive a cash  payment from Ciba  with
respect  to options outstanding on November 20, 1994, equal to (A) 37.33 percent
of the number of shares of Common  Stock with respect to which each such  option
would  first  become exercisable  in calendar  year 1995  multiplied by  (B) the
difference between  $117 per  share and  the exercise  price per  share of  such
option  with respect to such shares ("1995 Cash Payments"). In fiscal year 1995,
the Company  paid  1995  Cash  Payments  to  eligible  option  holders  totaling
approximately  $24,124,000 and Ciba  reimbursed the Company  for such amounts as
well as  payroll taxes  totaling approximately  $1,453,000 associated  with  the
payments.  With respect to the remaining shares  of Common Stock subject to each
such option (i.e., those shares with  respect to which the option first  becomes
exercisable  before  or  after  1995),  each  optionee  was  granted  the right,
exercisable at any  time during  which such  option remains  outstanding and  is
exercisable  with respect  to such  shares, to  surrender for  cancellation that
portion of such option relating to 37.33 percent of such shares in return for  a
cash  payment from Ciba equal  to (A) the difference  between $117 per share and
the exercise price  per share of  such option  multiplied by (B)  the number  of
shares with respect to which such option is so surrendered and canceled ("Option
Participation   Payment").  In   fiscal  year  1995,   Ciba  paid  approximately
$59,541,000 to  eligible option  holders in  connection with  the surrender  for
cancellation  of  such  options and  reimbursed  the Company  for  payroll taxes
totaling approximately $1,447,000 associated with the payments.
 
    The grant and  exercise of  any 1995  Cash Payment  or Option  Participation
Payment right with respect to any executive officer (i.e., an officer subject to
Section  16 of the Exchange Act) or director  of the Company was approved by the
Compensation Committee and was made subject to stockholder approval of the grant
of such right  at the  Company's 1995  stockholder meeting,  which approval  was
received  on  May 18,  1995. Under  the  terms of  the Investment  Agreement, as
amended, Ciba agreed  that once  stockholder approval was  obtained, Ciba  would
make all such payments to executive officers and directors to which such persons
would  have been entitled at  the Closing, increased at a  rate of 6 percent per
annum calculated from the Closing to the date such payment was actually made  by
Ciba, provided that such increased payments were
 
                                       24
<PAGE>
required  only  for  payment  rights  exercised  within  5  business  days after
stockholder approval was  obtained. Under this  provision, Ciba made  cumulative
interest  payments of approximately $845,000 to the Company's executive officers
and directors in connection with their exercise of payment rights.
 
    The Company agreed that if any of the above-described cash payments by  Ciba
to  Chiron executive officers, alone or  when aggregated with other compensation
payable to any such executive officers, constitute an "excess parachute payment"
within the meaning of Section  280G of the Internal  Revenue Code and/ or  would
subject  such individuals to  a tax under  Section 4999 of  the Internal Revenue
Code, the Company  may pay  such executive  officers such  additional amount  or
amounts  as shall be  necessary to assure  that, on any  date, the net after-tax
amount realized  by such  executive officers  from the  compensation paid  as  a
result  of such cash payments from Ciba  plus such additional amount shall equal
the net after-tax amount that such individuals would have realized from the cash
payment from Ciba if such additional tax were not imposed.
 
    During 1995, in connection with the Company's acquisition of CCD from  Ciba,
the Company and Ciba each contributed $12.5 million to pay transitional costs to
preserve  through the date  of the acquisition the  value of retirement benefits
earned by CCD employees under its defined benefit retirement plan. In  addition,
Ciba  and  the  Company  each  contributed  approximately  $500,000  to  resolve
transitional issues  affecting  CCD's employee  post-retirement  life  insurance
benefits.
 
    In  1990, the  Company entered into  agreements with Bios  Chile ("Bios"), a
Chilean biotechnology  company  in  which  Dr.  Pablo  Valenzuela,  Senior  Vice
President,  holds an ownership interest.  Dr. Bernardita Mendez, Vice President,
Regulatory and  Quality  Affairs, who  is  married  to Dr.  Valenzuela,  is  the
daughter  of the general manager of Bios.  Under the agreements, as amended: (a)
Dr. Valenzuela will be permitted to contribute up to 20 percent of his work time
in any year to Bios; (b) Chiron acquired 19 percent of the outstanding stock  of
Bios upon payment of $100,000, plus an option to acquire up to 50 percent of the
outstanding  stock  upon  payment of  an  additional $100,000;  (c)  Chiron will
contribute equipment to Bios with a value  of $250,000 in the first year of  the
agreement  and $50,000 a  year for ten  years thereafter; (d)  Chiron will pay a
maximum of $25,000 per year for each of the next ten years for reasonable  costs
and  expenses incurred by Dr. Valenzuela  while performing services for Bios. In
return, Bios will perform research services  for Chiron valued at not less  than
$200,000  in the first  year of the agreement  and $50,000 a  year for ten years
thereafter. The agreement between the companies further contemplates the  supply
of  certain biotechnological  services and supplies  by Bios to  Chiron having a
value of  no  less than  $100,000  in each  of  the three  years  following  its
effective  date.  Chiron will  have the  right  to commercialize,  outside Latin
America, any product of Bios and Bios will have the right to sell certain Chiron
reagents for research purposes. In fiscal year 1995, the Company paid to Bios  a
total  of $78,100  under various  provisions of  the above-mentioned agreements.
Under a separate letter of intent  relating to development of protocols for  the
Company's  subsidiary CCD, CCD made a payment  to Bios of $25,000 in fiscal year
1995. The Company anticipates that a  definitive agreement between CCD and  Bios
will  be signed, under the terms of which Bios would undertake the research work
agreed upon for a fee of approximately $125,000.
 
    Mr. Lewis Coleman, a director of the Company, was Chief Financial Officer of
BankAmerica Corp. until December 1995. During fiscal year 1995, the Company paid
approximately $74,000 to a BankAmerica Corp. subsidiary in fees incurred in  the
ordinary  course of business in  connection with the management  of a portion of
Chiron's investment  portfolio.  The  Company  also  maintains  routine  banking
relationships  with Bank  of America  N.T. &  S.A., a  subsidiary of BankAmerica
Corp. The Company  believes that  fees and costs  associated with  all of  these
services are customary and reasonable in relation to the services rendered.
 
    Mr.  Jack W. Schuler, a  director of the Company,  is chairman of Stericycle
Corporation, a company  that processes, sterilizes  and recycles medical  waste.
During  fiscal year  1995, the Company  and its  subsidiaries paid approximately
$93,000 to Stericycle for services rendered.
 
    Mr. C. William  Zadel, Vice  President and  Chief Executive  Officer of  CCD
until  his resignation on December 31, 1995,  entered into an agreement with the
Company in June 1995 regarding the termination of his employment which  provides
the  following:  (i) in  lieu  of any  payment  for 1995  under  CCD's long-term
incentive plan, CCD agreed to pay him $171,200 following the termination of  his
employment;  (ii) on January 1, 1996, and January 1, 1997, CCD agreed to pay him
lump sum payments of $650,560 and $325,280,
 
                                       25
<PAGE>
respectively, which  amounts represent  approximately 18  months of  salary  and
target short-term and long-term cash compensation; (iii) in the event he has not
accepted a successor position by July 1997, CCD will pay him a monthly severance
amount  of $54,213  per month  up to  6 months  and $28,533  per month  up to an
additional 6 months, until he accepts a successor position, but in no event  for
more  than  12  months in  the  aggregate;  (iv) until  he  accepts  a successor
position, CCD will maintain  in effect for his  benefit the medical, dental  and
life  insurance coverage he held in June 1995,  but in no event for more than 30
months after  the  termination  of  his  employment; and  (v)  in  lieu  of  his
participating  in the  post-retirement medical program  established for eligible
CCD employees following the acquisition of CCD by the Company, the Company  will
pay him a lump sum of $33,000.
 
    In  September 1990, Mr. William Green,  Senior Vice President, Secretary and
General Counsel, entered into an agreement with the Company which provides  that
the  Company will maintain life insurance for  him in the amount of $500,000 and
that in the event Mr. Green's  contributions or premiums associated with  health
or  dental insurance exceed $4,500 in any year, the Company will pay the excess.
Mr. Green's agreement with  the Company further provides  that in the event  the
Company  terminates his employment without cause, all options to purchase shares
of Common Stock of  the Company granted to  Mr. Green on his  date of hire  will
immediately  vest. All such options had vested in accordance with their terms by
December 31, 1995.
 
    Pursuant to the provisions of an executive loan program adopted by the Board
of Directors to promote stock  ownership by executive officers ("Executive  Loan
Program"),  in December  1995, the  Company provided a  loan of  $351,250 to Mr.
Green to enable him to purchase 10,000 shares of Chiron Common Stock through the
exercise of a  stock option.  Mr. Green  agreed: (1)  to pledge  to the  Company
10,000  shares of Chiron Common  Stock acquired by him  as security for the loan
and (2) that the shares will be subject to an additional restriction on transfer
which will lapse as to fifty (50) percent  of the shares after one year and  the
remainder after two years. The loan bears an interest rate of 8.5 percent and is
due  in full  on or prior  to December  29, 1997. As  of December  31, 1995, the
amount outstanding on the loan to  Mr. Green, including interest, was  $351,250.
During  the fiscal year ended December 31, 1995, the largest aggregate amount of
indebtedness outstanding on the loan was $351,250.
 
    The Company  has  made several  loans  to  Dr. Dino  Dina,  Vice  President,
Virology  and  Vaccine Development,  and President,  Chiron Biocine  Company, to
assist him in the rebuilding of  his residence following its destruction in  the
October  1991 Oakland/Berkeley fire and pending resolution of insurance coverage
disputes. In December 1992 and January 1993, the Company loaned Dr. Dina a total
of $200,000 at a variable  prime interest rate. The loan  was due in full on  or
prior  to December  8, 1995. On  April 1, 1993,  the Company loaned  Dr. Dina an
additional $200,000 at a variable prime interest rate. The loans were secured by
a second deed of trust  on the property and a  pledge of stock whereby Dr.  Dina
granted Chiron a security interest in 10,000 shares of Chiron Common Stock owned
by  him. On April 12, 1994, Dr. Dina partially repaid the loans made in December
1992 and January 1993. On January 31, 1995, Dr. Dina repaid in full the  amounts
outstanding  on  the  two  remaining  loans.  The  largest  aggregate  amount of
indebtedness outstanding during the fiscal year  ended December 31, 1995 on  the
two loans to Dr. Dina was $296,543.
 
    Pursuant  to the provisions of the Executive Loan Program, in December 1993,
the Company provided a loan  of $408,000 to Dr. Dina  to enable him to  purchase
34,000 shares of Chiron Common Stock through the exercise of a stock option. Dr.
Dina  agreed: (1) to pledge to the  Company 34,000 shares of Chiron Common Stock
acquired by him as security for the  loan; (2) that the shares would be  subject
to  an additional  restriction on  transfer which would  lapse as  to fifty (50)
percent of the shares after one year  and the remainder after two years and  (3)
that  in the event he left  the employ of the Company  prior to the lapse of the
transfer restriction, for any reason  other than death or permanent  disability,
the  shares  then subject  to  a restriction  on  transfer would  be  subject to
repurchase by the Company at the original stock option exercise price. The  loan
bore  an interest  rate equal  to the average  yield on  the Company's aggregate
investment portfolio  adjusted quarterly  and was  due in  full on  or prior  to
December  8,  1998. On  January 31,  1995, Dr.  Dina repaid  in full  the amount
outstanding on this loan.  During the fiscal year  ended December 31, 1995,  the
largest aggregate amount of indebtedness outstanding on the loan to Dr. Dina was
$428,100.
 
                                       26
<PAGE>
    In September 1994, the Company provided a loan of $200,000 to Dr. William J.
Link, Vice President of the Company and Chief Executive Officer of Chiron Vision
Corporation,  to assist him in financing his principal residence. The loan has a
fixed interest rate of 7.75 percent and is due in full on or prior to  September
2,  1999. The loan is secured  by a second deed of  trust on the property. As of
December 31, 1995,  the amount outstanding  on the loan  to Dr. Link,  including
interest, was $203,875. The largest aggregate amount of indebtedness outstanding
during  the fiscal  year ended  December 31, 1995  on the  loan to  Dr. Link was
$203,875.
 
    In October 1993, the Company  provided a loan of  $400,000 to Dr. Mickey  S.
Urdea,  Vice President, Nucleic Acid Systems Research and Development, to assist
him in the renovation of a residence.  The loan bears an interest rate equal  to
the  average  yield on  the  Company's aggregate  investment  portfolio adjusted
quarterly. In December 1995, Dr.  Urdea partially repaid the amount  outstanding
on  the loan  and the  Company agreed to  extend the  due date  of the remaining
amount from October  11, 1995, to  October 11, 1996.  The loan is  secured by  a
second  deed of trust on the property.  As additional security for the loan, Dr.
Urdea has  agreed to  transfer  to the  Company  stock underlying  vested  stock
options  to  purchase 3,000  shares  of Chiron  Common  Stock held  by  him when
acquired. As of December  31, 1995, the  amount outstanding on  the loan to  Dr.
Urdea,  including  interest,  was  $335,832.  The  largest  aggregate  amount of
indebtedness outstanding during the fiscal year  ended December 31, 1995 on  the
loan to Dr. Urdea was $392,818.
 
    In  October and November 1992, prior to his becoming an executive officer of
the Company, the  Company provided  two loans  totaling $183,000  to Mr.  Robert
Blackburn,  Vice  President  and Chief  Patent  Counsel,  to assist  him  in the
purchase of a  primary residence.  The first loan  for $133,000  had a  variable
prime  interest rate, was  due in full  on or prior  to April 25,  1995, and was
secured by a  pledge of stock  whereby Mr. Blackburn  granted Chiron a  security
interest  in 36,000 shares of Chiron  Common Stock underlying stock options held
by him. The second loan for $50,000 had a variable prime interest rate, was  due
in full on or prior to April 25, 1995, and was secured by a second deed of trust
on  the property. On  April 18, 1995,  Mr. Blackburn repaid  in full the amounts
outstanding on  the two  loans.  The largest  aggregate amount  of  indebtedness
outstanding  during the fiscal year ended December  31, 1995 on the two loans to
Mr. Blackburn was $187,151.
 
    In February 1994,  in connection  with his recruitment  and relocation,  the
Company  provided a loan of $450,000 to Dr. David Martin, Senior Vice President,
and President, Chiron Therapeutics  until April 30, 1995,  to assist him in  the
purchase  of a residence. The  loan bore a variable  prime interest rate and was
due in full on or prior  to February 9, 1999. The  loan was secured by a  second
deed  of trust  on Dr.  Martin's property in  Pennsylvania. Dr.  Martin left the
Company in April  1995 and  all amounts outstanding  on Dr.  Martin's note  were
repaid  on his behalf. The largest  aggregate amount of indebtedness outstanding
during the fiscal year  ended December 31,  1995 on the loan  to Dr. Martin  was
$474,645.
 
    In  August 1994, the  Company provided a  loan of $200,000  to Mr. Dennis L.
Winger, Senior Vice President and Chief Financial Officer, to assist him in  the
purchase  of real property. The  loan bore an interest  rate of 7.25 percent and
was due in full on or  prior to June 1, 1996. The  loan was secured by a  second
deed  of trust on  Mr. Winger's residence.  In July 1995,  Mr. Winger repaid the
loan in full. The  largest aggregate amount  of indebtedness outstanding  during
the fiscal year ended December 31, 1995 on the loan to Mr. Winger was $200,000.
 
    In  January 1995, prior to his becoming an executive officer of the Company,
the Company provided a loan of  $150,000 to Mr. Mario Lorenzoni, Vice  President
and  Chief Executive Officer of Biocine S.p.A. The loan bore an interest rate of
8.5 percent and was  due in full  on or prior  to March 30,  1995. The loan  was
secured  by a pledge  of stock whereby  Mr. Lorenzoni granted  Chiron a security
interest in 4,316 shares of Chiron Common Stock underlying stock options held by
him. Mr.  Lorenzoni  repaid the  loan  in full  in  February 1995.  The  largest
aggregate  amount  of  indebtedness  outstanding during  the  fiscal  year ended
December 31, 1995 on the loan to Mr. Lorenzoni was $151,398.
 
    In July  1995, the  Company's  subsidiary Chiron  b.v.  provided a  loan  of
$150,000  to Mr.  Alain Herrera, Vice  President and President,  Chiron b.v., to
assist  him   in   the  purchase   of   real   property.  The   loan   bore   an
 
                                       27
<PAGE>
interest  rate of 5.5 percent and was due in  full on or prior to July 10, 1998.
The loan was secured by a second  deed of trust on Mr. Herrera's residence.  Mr.
Herrera repaid the loan in full in October 1995. The largest aggregate amount of
indebtedness  outstanding during the fiscal year  ended December 31, 1995 on the
loan to Mr. Herrera was $149,026.
 
    The Company has indemnification agreements  with directors that (i)  confirm
the  present indemnity provided  to them by  the Company's Bylaws  and give them
assurances that  this indemnity  will  continue to  be provided  despite  future
changes in the Bylaws and (ii) provide that, in addition, the directors shall be
indemnified  to  the  maximum  extent  permitted  by  law  against  all expenses
(including attorneys' fees), judgments,  fines, and settlement amounts  incurred
or  paid by them in any action or  proceeding, including any action by or in the
right of the  Company, on account  of their  service as a  director, officer  or
similar  official of any  other company or  enterprise when they  are serving in
such capacities at the  request of the  Company. The indemnification  agreements
further provide that expenses incurred by a director in such cases shall be paid
by the Company in advance, subject to the director's obligation to reimburse the
Company  in  the event  it is  ultimately  determined that  the director  is not
entitled to be indemnified for such expenses under any of the provisions of  the
indemnification  agreement.  However,  no  indemnity  will  be  provided  to any
director under the agreements as described in clause (ii) of the first  sentence
of  this  paragraph  on account  of  conduct  which is  finally  adjudged  to be
knowingly  fraudulent,  deliberately   dishonest,  or   to  constitute   willful
misconduct.  In addition, no  indemnification will be provided  if a final court
adjudication shall  determine that  such indemnification  is not  lawful, or  in
respect  of any  suit in which  judgment is  rendered against a  director for an
accounting of profits made from a purchase or sale of securities of the  Company
in  violation  of Section  16(b)  of the  Securities  Exchange Act  of  1934, as
amended,  or  of  any  similar  statutory  provision,  or  on  account  of   any
remuneration  paid to a director which is  finally adjudged to have been paid in
violation  of  law.  The  indemnification  agreements  also  contain  provisions
designed to protect the Company from unreasonable settlements or redundant legal
expenditures.
 
                                  PROPOSAL 2:
                    APPROVAL OF AMENDMENT TO CHIRON RESTATED
                          CERTIFICATE OF INCORPORATION
 
    On  February 23,  1996, the  Chiron Board  approved, subject  to stockholder
approval, an amendment  to Chiron's Restated  Certificate of Incorporation  (the
"Chiron  Certificate")  increasing the  number of  shares  of Common  Stock that
Chiron is authorized to issue from 100 million to 500 million (the "Amendment").
 
    The Chiron  Board has  determined  that an  increased number  of  authorized
shares  of Chiron Common  Stock is in the  best interest of  the Company and its
stockholders. Chiron intends  to use  authorized and unissued  shares of  Chiron
Common  Stock for  various corporate  purposes, including,  but not  limited to,
possible   future    financing    and   acquisition    transactions,    possible
recapitalization  through a stock  split or stock  dividend, and other corporate
purposes. Authorized and unissued  shares of Chiron Common  Stock may be  issued
for   the  foregoing  purposes  by  the  Chiron  Board  without  further  Chiron
stockholder action being necessary unless the  issuance is in connection with  a
transaction   for  which  stockholder  approval   is  otherwise  required  under
applicable law, regulation or agreement.
 
    Pursuant  to  the  Fifth  Article  of  the  Chiron  Certificate,  Chiron  is
authorized  to issue  100 million  shares of Common  Stock. If  the Amendment is
approved, such number will be increased to 500 million. As of February 29, 1996,
there were 42,108,818 outstanding shares  of Chiron Common Stock. An  additional
10,955,202  shares of Chiron  Common Stock have been  reserved for issuance upon
exercise of stock options, warrants and upon conversion of Chiron's and  Cetus's
Debentures  convertible into  Chiron Common  Stock on  or before  2000 and 2002,
respectively, unless previously redeemed.
 
    If this proposal is  adopted by Chiron stockholders,  the first sentence  of
the  Fifth Article of the Chiron Certificate and Subpart 2 of said Fifth Article
will read as follows:
 
       FIFTH:  This  corporation is  authorized to issue  two classes  of
       shares  to  be  designated,  respectively,  "Preferred  Stock" and
       "common stock". The total number of shares which this  corporation
       is authorized to issue is five hundred five million (505,000,000).
       Five
 
                                       28
<PAGE>
       million  (5,000,000)  shares  shall be  Preferred  Stock  and five
       hundred million (500,000,000)  shares shall be  common stock.  The
       Preferred  Stock shall  have a par  value of $0.01  per share; the
       common stock shall have a par value of $0.01 per share.
 
       2.  COMMON STOCK
 
       The common stock may be  issued from time to  time in one or  more
       series.  Four  Hundred Ninety-nine  million five  hundred thousand
       (499,500,000)  shares  of  common  stock  are  designated  "Common
       Stock."  All  other  series  of  common  stock  shall collectively
       consist of five  hundred thousand  (500,000) shares  and shall  be
       designated, as a group, "Restricted Common Stock."
 
    The  full text of the Fifth Article of the Chiron Certificate reflecting the
Amendment is attached as Annex 1 and is incorporated by reference.
 
VOTE REQUIRED FOR APPROVAL OF AMENDMENT TO CHIRON RESTATED CERTIFICATE OF
INCORPORATION.
 
    The affirmative vote  of a  majority of the  shares of  Common Stock  having
voting  power present in person or represented by proxy, a quorum being present,
is necessary  to  approve the  Amendment  to Chiron's  Restated  Certificate  of
Incorporation.
 
    THE  BOARD  OF DIRECTORS  RECOMMENDS A  VOTE FOR  THE PROPOSED  AMENDMENT TO
CHIRON'S RESTATED CERTIFICATE OF INCORPORATION TO INCREASE THE AUTHORIZED NUMBER
OF SHARES OF COMMON STOCK OF THE COMPANY FROM 100 MILLION TO 500 MILLION.
 
                                  PROPOSAL 3:
                     APPROVAL OF AMENDED STOCK OPTION PLAN
 
GENERAL
 
    The Board  of  Directors  has  adopted,  subject  to  stockholder  approval,
amendments  to the Chiron 1991 Stock Option  Plan ("Plan" or "1991 Plan"), which
include:
 
    (1) Changes to the automatic annual stock option grant program of the  Plan,
which  implement a new  formula for determining the  number of shares underlying
the  automatic  stock  options  granted  to  non-employee  directors.  The  Plan
currently  provides for the automatic annual  grant to non-employee directors of
stock options on 3,000 shares of Common Stock. As amended, this annual automatic
grant will be calculated based upon the average stock price of the Common  Stock
over the preceding 12-month period. Based on this average stock price, if annual
stock  options to  each non-employee director  had been granted  on February 29,
1996, 1289 shares of Common Stock would  have been subject to each such  option.
The  amended Plan also provides for  additional automatic awards to non-employee
directors in the form of "automatic share rights."
 
    (2) The provision of performance  units, which are restricted shares,  share
rights  and share units awarded to corporate vice presidents and other executive
officers designated by  the Compensation Committee  ("162(m) executives")  which
comply  with the requirements  of Internal Revenue  Code ("Code") Section 162(m)
("performance units"). The performance units would vest based on the  attainment
of  one or more  pre-established performance goals  over a specified performance
period. The administration of the performance  units is intended to satisfy  all
requirements  imposed by  Section 162(m)  to prevent  the application  of the $1
million annual deduction limit on executive compensation to certain awards under
the Plan.
 
    The 1991 Plan was adopted originally by the Board of Directors ("Board")  on
June  14, 1991,  and, as subsequently  amended, was approved  by stockholders on
December 10, 1991, May 13, 1993, and May 18, 1995. Any awards granted under  the
amended  provisions of the Plan will be granted subject to stockholder approval.
If stockholder approval is not obtained, awards under the Plan will continue  to
be  granted in accordance  with the Plan  provisions in effect  before the Board
adopted the  amendments. As  of January  1, 1996,  approximately 3986  employees
(including   officers   and   directors),   28   independent   contractors   and
 
                                       29
<PAGE>
consultants, and 8  non-employee directors  are eligible to  participate in  the
Plan. The Plan, as proposed to be amended ("Amended Plan"), is attached as Annex
2,  to which reference is made for  a complete statement of the Plan provisions.
The market price of Chiron Common Stock  on February 29, 1996 was $111.375.  The
following  summary  of  certain Amended  Plan  provisions is  qualified,  in its
entirety, by reference to the Amended Plan.
 
GENERAL DESCRIPTION OF CHIRON 1991 STOCK OPTION PLAN AS AMENDED
 
    Pursuant to Securities and Exchange Commission rules, the Plan is  described
below in its entirety, incorporating the proposed amendments.
 
PURPOSE
 
    The purpose of the Plan is to enable Chiron to attract and retain employees,
including   officers   and   directors,   non-employee   directors,  independent
contractors and  consultants  and to  offer  incentives and  rewards  that  will
encourage  such individuals to acquire a proprietary interest in the Company, to
build value for stockholders, and to continue in the service of the Company  and
its subsidiaries.
 
ADMINISTRATION
 
    The  Plan is  administered by  a committee  or committees  (the "Committee")
appointed by the Board from among  its members. Administration of the Plan  with
respect to officers subject to Section 16 of the Exchange Act will be by members
who are "disinterested persons" as that term is defined in Rule 16b-3 under that
Act.  With  respect to  establishing,  administering and  certifying performance
units, the composition of the Committee is intended to comply with Code  Section
162(m).  The Committee  is generally  authorized to  construe and  interpret the
Plan, to  establish  appropriate rules  and  regulations, to  select  employees,
independent  contractors and consultants of the Company and its subsidiaries for
participation and to specify the terms of awards granted under the Plan. Members
of the  Committee  may  be removed  by  the  Board. In  determining  the  terms,
conditions and amount of each award, the Committee may take into account various
criteria,  including,  among others,  salary  grade and  individual  and Company
performance.
 
    Chiron will pay all costs of  administration of the Plan. The cash  proceeds
received by Chiron from the issuance of shares pursuant to the Plan will be used
for general purposes.
 
SHARES AND TERM
 
    The  stock subject to  awards granted under the  Plan is Chiron's authorized
but unissued or  reacquired Common Stock  ("Common Stock") or  shares of one  or
more  series of Chiron's authorized but unissued or reacquired Restricted Common
Stock  (in  the  aggregate,  "Company  Stock").  The  rights,  preferences   and
privileges, together with restrictions and limitations, and the number of shares
of  each series of Restricted Common Stock  issuable under the Plan, will be set
forth in Chiron's Certificate of Determination of Preferences of Common Stock as
in effect  from time  to time  during  the term  of the  Plan. The  Company  may
repurchase shares in the open market or otherwise.
 
    Initially,  the stockholders approved for issuance under the Plan, 4,500,000
shares of Company Stock  in addition to the  shares of Company Stock  previously
authorized   by  stockholders  and  remaining  for  issuance  under  the  Chiron
Corporation 1982 Stock Option Plan ("1982 Plan") and the Chiron Corporation 1984
Non-Qualified Plan ("Non-Qualified Plan") on December 10, 1991 (897,204 shares).
Except as otherwise  limited by  the terms  of this  Plan, this  amount will  be
subject to adjustment annually, without further stockholder approval, commencing
on  January  1, 1992,  to  authorize the  grant of  awards  upon that  number of
additional shares of Company Stock equal to 1.50 percent of the number of Chiron
Common Equivalent Shares outstanding as of the end of the preceding fiscal year.
"Chiron Common Equivalent Shares" are the total number of shares of Common Stock
outstanding plus  the total  number  of shares  of  Common Stock  issuable  upon
conversion   or  exercise  of  outstanding  warrants,  options  and  convertible
securities. Not more than 4,500,000 shares of Company Stock, plus the number  of
shares  of Company  Stock remaining  for issuance  under Chiron's  1982 Plan and
Chiron's Non-Qualified Plan on the effective date of this Plan may be subject to
Incentive Stock Options ("ISO") granted under  this Plan. In no event will  more
than 500,000 shares of Restricted Common Stock be issued under this Plan.
 
                                       30
<PAGE>
    To  the extent that  an option expires  or is terminated,  or is canceled or
forfeited for  any  reason  (other  than surrendered  for  a  cash  appreciation
payment)  without having been exercised in  full, any remaining shares allocable
to the  unexercised portion  of such  option shall  again become  available  for
subsequent grants under the Plan. To the extent that a share right or share unit
expires  or is terminated,  or is canceled  or forfeited for  any reason without
being paid in cash or shares of Company Stock, any remaining shares allocable to
the unpaid portion  of such  share right or  share unit  shall become  available
again  for subsequent  grants under the  Plan. Restricted shares  that have been
issued but forfeited or  repurchased by the Company  shall not be available  for
the  grant of new awards under the Plan. Shares attributable to the payment of a
share unit in cash, and the payment of cash or a cash appreciation  distribution
upon the surrender or exercise of a stock option, or the payment of cash in lieu
of  shares under a  restricted share or  a share right,  and shares forfeited or
repurchased by Chiron pursuant to its forfeiture and repurchase rights under the
Plan will not be available for subsequent grants under the Plan.
 
    No individual may receive awards under  the Plan over its term with  respect
to more than 1 million shares of Common Stock.
 
ELIGIBILITY
 
    Employees,   including  officers  and   directors,  non-employee  directors,
consultants and independent contractors of the Company or its subsidiaries,  are
eligible  to  receive  awards  under the  Plan.  162(m)  executives  may receive
performance unit awards in addition to or in lieu of other awards granted  under
the  Plan. Non-employee  directors are  eligible only  for automatic  awards, as
described below.
 
GRANTS TO AWARD HOLDERS OF STOCK OPTIONS, RESTRICTED SHARES, SHARE RIGHTS, SHARE
UNITS, AND PERFORMANCE UNITS
 
    The Committee may,  from time to  time, grant  awards to one  or more  award
holders  that it determines is eligible to participate in the Plan. An award may
be in the form of a stock option, restricted share, share right, share unit,  or
performance unit.
 
    In  order to  assist an  award holder  in the  acquisition of  Company Stock
pursuant to an award, the Committee may authorize the Company to extend  secured
or  unsecured credit to the  award holder (other than  pursuant to the automatic
award provisions of the Plan). The Committee may also permit an award holder  to
elect  to have shares of the Company's Common Stock held by the award holder for
the requisite period to  avoid a charge to  the Company's earnings  ("Previously
Owned  Shares") applied  to satisfy any  withholding tax  obligation incurred in
connection with the  award and may  require or  permit a portion  of any  Common
Stock  otherwise issuable under an award to be paid in cash instead of stock and
applied to such a withholding tax obligation.
 
    STOCK OPTIONS
 
    Under the terms of the Plan, the Committee may grant an ISO, which satisfies
the requirements of Section 422 of the Code, or a non-statutory option  ("NSO"),
which is not intended to satisfy the requirements of Section 422 of the Code.
 
    The  Committee may determine the number  of shares of Company Stock issuable
under an  option as  well as  the exercise  date, the  exercise price,  and  the
exercise  period of an option. However, the  exercise price of an option may not
be less  than eighty-five  percent (85  percent) of  the fair  market value  (as
defined  in the  Plan) of  the option  shares on  the date  of the  grant of the
option, or in the case of an ISO, one hundred percent (100 percent) of the  fair
market  value of the option  shares on the date  of the option grant. Generally,
effective August 13, 1993, except for substitute options as defined in the  1991
Plan,  fair market value of a share of Common Stock on any relevant date will be
the average between  the reported high  and reported  low price on  the date  in
question  of one  share of  Common Stock on  the Nasdaq  National Market System,
rather than being based on a ten (10) day average as had previously been used to
determine fair market value under the 1991 Plan.
 
    The duration of  an option  may not  exceed ten  years. Notwithstanding  the
foregoing,  substitute options (defined below)  will have exercise prices, terms
and conditions determined in accordance with the relevant
 
                                       31
<PAGE>
option agreements  and  adjusted,  where applicable,  for  their  conversion  to
options on Chiron Common Stock, and the terms of automatic option grants will be
as described under "Automatic Awards to Non-Employee Directors."
 
    Following stockholder approval of the 1991 Plan and upon consummation of the
mergers  between Chiron and  Cetus, Protos, and  Chiron Ophthalmics, outstanding
options under  those companies'  stock option  plans and  Chiron's prior  option
plans  (including related limited stock  appreciation rights) were converted, in
the manner and at  the exchange ratio specified  in the merger agreements,  into
options  to acquire Common Stock  under this Plan. On  the Effective Date of the
Plan, outstanding  automatic  option grants  under  the Chiron  1982  Plan  were
conformed,  other than to extend the term,  to the automatic option grants under
the Plan. Collectively, these options will be known as "substitute options."
 
    The exercise  price  is  generally  payable  in full  in  cash  or,  in  the
Committee's discretion, in Previously Owned Shares or, under certain conditions,
the  proceeds  of a  same day  sale  of the  award shares,  or  by means  of the
extension of secured or unsecured credit to the optionee.
 
    RESTRICTED SHARES, SHARE RIGHTS, AND SHARE UNITS
 
    Restricted  shares,  share   rights,  and   share  units   may  be   granted
independently  of  other  compensation or  in  lieu of  compensation  that would
otherwise be paid in cash or stock options, whether at the election of the award
holder or otherwise.  The number  of restricted  shares, share  rights or  share
units  to be awarded in lieu of any  cash compensation amount or number of stock
options shall be determined by the Committee in its sole discretion and need not
be equal to such foregone compensation in fair market value. Restricted  shares,
share  rights and share  units may be  awarded in tandem  with stock options, so
that a portion  of such award  becomes payable or  becomes free of  restrictions
only  if and  to the  extent that the  tandem options  are not  exercised or are
forfeited, subject to such  terms and conditions as  the Committee may  specify.
The  terms, conditions and restrictions to which restricted shares, share rights
and share units are  subject will be  determined in the  sole discretion of  the
Committee,  and  may vary  from grant  to grant.  The Committee  shall determine
whether any consideration is to be  received by the Company or its  subsidiaries
as  a condition precedent to the issuance  of restricted shares or shares issued
pursuant to share rights.
 
    With respect  to  restricted shares  and  share rights,  the  Committee  may
provide  award holders  with an  election to receive  a percentage  of the total
value of the Company Stock subject to their restricted shares or share rights in
the form of a cash payment,  subject to such terms, conditions and  restrictions
as the Committee shall specify.
 
    A. Restricted Shares
 
    Restricted shares are shares of Company Stock, the retention and transfer of
which  is  subject  to terms  and  conditions (based  on  performance standards,
periods of service or  otherwise) determined by the  Committee. At the time  the
restricted  share  award is  made, the  Committee  will establish  a restriction
period applicable to such award. Generally, the award holder will have the right
to enjoy all  stockholder rights during  the restriction period,  except that  a
breach  of the terms and conditions established by the Committee pursuant to the
restricted share award will cause a  repurchase or forfeiture of the  restricted
share award.
 
    B. Share Rights
 
    A  share right consists of the right, subject to terms and conditions (based
on performance  standards, periods  of service  or otherwise)  as the  Committee
shall  establish, to receive shares  of Company Stock, and  if determined by the
Committee, cash dividend equivalents.
 
    C. Share Units
 
    A share unit consists of the right to receive an amount in cash equal to the
fair market value of one share of Company Stock on the date of valuation of  the
unit,  including, if  determined by the  Committee, a  cash dividend equivalent,
less such amount, if  any, as the Committee  shall specify. The Committee  shall
determine  the terms and conditions (based  on performance standards, periods of
service or otherwise), if any,  to which any such  payment will be subject.  The
award  holder  shall not  be entitled  to any  interest in  or to  any dividend,
voting, or other rights of a stockholder.
 
                                       32
<PAGE>
    D. Performance Units
 
    Effective  March  8,  1996,  162(m)  executives  are  eligible  to   receive
performance units which consist of a restricted share, share right or share unit
that  vests upon the attainment of pre-set performance goals (established by the
Committee) over  a specified  performance  period. The  Committee  administering
performance  units  is  intended to  satisfy  the requirements  of  Code Section
162(m). The  Committee may  provide for  different levels  of payouts  based  on
relative performance toward a performance goal. Final payouts are subject to the
approval  of the  Committee, and  the Committee  has the  absolute discretion to
reduce or cancel, but not increase, any payout.
 
    Performance units may be based on one or more of the following criteria over
a specified period:  total shareholder  return; the achievement  of a  specified
closing  or average  closing price of  Common Stock; the  absolute or percentage
increase in the closing or average closing  price of Common Stock and/or one  or
more  of the following  measures of the  Company's net income  for the specified
performance period determined in  accordance with generally accepted  accounting
principles  as consistently  applied by  the Company:  absolute net  income or a
percentage or absolute dollar  increase in net income,  earnings per share or  a
percentage  or  absolute dollar  increase in  earnings per  share, or  return on
assets employed or equity or a percentage or absolute dollar increase in  return
on  assets employed  or equity;  or the Company's  absolute gross  revenues or a
percentage or  absolute dollar  increase  in gross  revenues for  the  specified
performance  period determined in accordance  with generally accepted accounting
principles as consistently applied by the Company. The performance units may  be
based  on the Company's  performance alone, or the  Company's performance may be
measured  against  variously  weighted  published  benchmark  indices  that  the
Committee  determines  are representative  of  the Company's  peer  group, which
indices may  include the  Standard &  Poor's Health  Care Composite  Index,  the
Standard  & Poor's Health Care Diversified  Index, the AMEX Biotechnology Index,
among others.
 
    For purposes of the Plan, net income and gross revenues shall be net  income
and  gross revenues of the Company and its consolidated subsidiaries as reported
by the Company  and certified  by its  independent public  accountants, but  the
Committee  in fixing any  goal may exclude any  or all of  the following if they
have a  material  effect on  annual  net income  or  gross revenues:  events  or
transactions that are either unusual in nature or infrequent in occurrence (such
as  restructuring/reorganization  charges, the  purchase or  sale of  in process
technology, the  sale or  discontinuance  of a  business  segment, the  sale  of
investment  securities, losses from litigation, the cumulative effect of changes
in accounting  principles, and  natural  disasters), depreciation,  interest  or
taxes.
 
CORPORATE TRANSACTIONS
 
    In  the event of an agreement to dispose  of all or substantially all of the
assets or outstanding capital stock of the  Company by means of a sale,  merger,
reorganization,  or liquidation ("Corporate Transaction"), each of the following
awards will  be  automatically accelerated  so  that (1)  options  become  fully
exercisable  with respect  to the total  number of shares  purchasable under the
options, (2)  restrictions on  restricted  shares will  be eliminated,  and  the
shares  will  immediately  vest,  and  (3) share  rights  and  share  units will
immediately vest and  become payable.  The Committee  may also  provide for  the
automatic  termination of repurchase  rights upon the  occurrence of a Corporate
Transaction.
 
    However, the  terms and  conditions of  any outstanding  award will  not  be
changed if the award is either assumed by the successor corporation, or replaced
with a comparable award by the successor corporation.
 
AUTOMATIC AWARDS TO NON-EMPLOYEE DIRECTORS
 
    On  the last business day  of the second quarter of  each fiscal year of the
Company after March 8, 1996 ("automatic grant date"), each incumbent, continuing
non-employee director (including each director newly elected or appointed on the
automatic grant  date)  will automatically  receive  an NSO  ("automatic  option
grants")  to purchase that number of whole  shares of Common Stock determined by
dividing $100,000 by the average stock price of a share of Common Stock over the
preceding 12-month period. Each  person who is newly  elected or appointed as  a
non-employee  director  on  a  date  other than  an  automatic  grant  date will
 
                                       33
<PAGE>
receive, on the date of such election or appointment, an automatic option  grant
to purchase a pro rata number of shares of Common Stock, depending on the number
of  months the non-employee  director will serve  as a director  before the next
automatic grant date.
 
    Each automatic option grant will have the following terms: (1) the  exercise
price  will be equal to the fair market value of the Common Stock on the date of
grant, payable in cash, or in shares  of Common Stock held at least six  months,
or  with the proceeds of a  same day sale of the  option shares; (2) the term of
the option will be ten years; (3) the option will expire if not exercised within
ninety days after the  optionee ceases to  serve as a  director, an employee,  a
consultant,  or an  independent contractor,  or within  twelve months  after the
optionee ceases to provide  such services due to  disability or death, (4)  each
automatic  option grant will be  exercisable at any time for  all or any part of
the number of granted shares, and (5)  the shares will be subject to  repurchase
by  the Company at the original exercise price if a non-employee director ceases
to provide services to Chiron or its subsidiaries as a director, an employee,  a
consultant or an independent contractor.
 
    The  Company's repurchase rights  will lapse and  the optionee's interest in
the purchased shares will vest in equal annual installments over five years from
the date of grant,  provided the optionee continues  to provide services to  the
Company.  However, the optionee will be  immediately and fully vested upon death
or disability.
 
    Each incumbent, continuing non-employee director elected or appointed before
March 8,  1996,  who is  serving  as such  on  the first  automatic  grant  date
occurring  after that  date, will  automatically be  granted, (i)  on that first
automatic grant date, the  right to receive shares  of Common Stock  ("automatic
share  right") for the number of whole shares purchasable with $40,000 ("$40,000
share right"),  and (ii)  on  each subsequent  automatic  grant date  while  the
individual  is serving as  a non-employee director, an  automatic share right to
purchase the number  of whole  shares purchasable with  $25,000 ("$25,000  share
right").  Each non-employee director  newly elected or  appointed after March 8,
1996 will automatically be  granted a $40,000  share right on  the date of  such
election  or appointment. On  each automatic grant date  occurring after the new
director's election or  appointment and  while the  individual is  serving as  a
non-employee director, the non-employee director will automatically be granted a
$25,000  share right. However, if the  non-employee director is newly elected or
appointed on  a date  other than  an automatic  grant date,  then on  the  first
automatic   grant  date  occurring  after  such  election  or  appointment,  the
non-employee director will be granted a pro rated $25,000 share right, based  on
the  number of  months the individual  served as a  non-employee director before
such automatic grant date. The dollar  values will be subject to  cost-of-living
increases.
 
    The share rights will vest in equal annual installments over five years from
the  date  of grant,  and shares  will be  issued in  satisfaction of  the share
rights, provided the non-employee director continues to provide services to  the
Company. However, the non-employee director will be immediately and fully vested
upon death or disability.
 
ADJUSTMENTS
 
    Options,  restricted shares, share  rights, share units,  and any agreements
evidencing such awards shall be subject to adjustment by the Committee as to the
number and,  if applicable,  price of  shares of  stock or  other  consideration
obligation  subject to such  awards in the  event of changes  in the outstanding
stock due to a change in the  corporate or capital structure of the Company.  In
the  event of any such change in  the outstanding stock, the aggregate number of
shares available under the Plan may be appropriately adjusted by the  Committee,
whose determination shall be conclusive.
 
CANCELLATION AND REGRANT OF OPTIONS
 
    Under  the Plan, the Committee has the authority to effect at any time, with
the consent  of the  affected option  holders, the  cancellation of  any or  all
options  outstanding under  this Plan, the  prior Cetus Stock  Option Plans, the
Protos Corporation 1988  Stock Option  Plan, the Chiron  Ophthalmics, Inc.  1986
Stock  Option Plan, the 1982 Plan and the Non-Qualified Plan (the "Prior Plans")
(other than options granted
 
                                       34
<PAGE>
under the automatic  option grant  provisions of these  plans) and  to grant  in
substitution  therefor new  options for the  same or different  number of shares
with an exercise price not less than 85 percent of fair market value on the  new
grant  date or 100 percent  of fair market value  if the new option  is to be an
ISO.
 
SURRENDER OF OPTIONS FOR CASH OR STOCK
 
    The Committee in its  discretion may implement  an option surrender  program
under  the Plan  through which one  or more  optionees may, under  the terms and
conditions established by the Committee, be  granted the right to surrender  all
or  part of an unexercised option for  an appreciation distribution equal to the
difference between the fair market value of the shares at the surrender date and
the option price  payable thereon. Such  distribution may be  made in shares  of
Company  Stock valued at fair market value on the date of surrender, in cash, or
partly in shares and partly in cash,  as the Committee, in its sole  discretion,
may  decide. The option surrender provisions are not applicable to the automatic
option grant provisions of the Plan.
 
REPURCHASE RIGHTS
 
    The Committee in  its discretion  may establish  as a  term of  one or  more
awards  granted  under the  Plan that  the  Company (or  its assigns)  will have
repurchase rights, exercisable upon the award holder's termination of employment
with, or  cessation of  services  for, the  Company  and its  subsidiaries.  The
Committee  will also have the authority to provide for the automatic termination
of the Company's repurchase  rights, in whole or  in part, thereby  accelerating
the  vesting of any or all of  the purchased shares (other than purchased shares
obtained pursuant to the  automatic option grant provisions  of this Plan)  upon
the occurrence of a Corporate Transaction.
 
RIGHT OF FIRST REFUSAL
 
    The  Committee in  its discretion  may establish  as a  term of  one or more
awards granted under the Plan that the Company has a right of first refusal with
respect to the  proposed disposition by  the award holder  (or any successor  in
interest by reason of purchase, gift or other mode of transfer) of any shares of
Company Stock acquired by the award holder. The instrument evidencing such right
of first refusal will specify the terms and conditions of that right.
 
SPECIAL CASH PAYMENTS RELATED TO CIBA-GEIGY TRANSACTION
 
    All holders of options to acquire shares of Common Stock under the 1991 Plan
on November 20, 1994 were granted certain cash payment rights in connection with
the Ciba transaction.
 
    Each optionee was granted the right to receive a cash payment from Ciba with
respect  to options outstanding on November 20, 1994, equal to (A) 37.33 percent
of the number of shares of Common  Stock with respect to which each such  option
would  first  become exercisable  in calendar  year 1995  multiplied by  (B) the
difference between  $117 per  share and  the exercise  price per  share of  such
option  with respect to such shares. The  portion of each option which underlies
each such  cash payment  is not  canceled  upon the  optionee's receipt  of  the
payment from Ciba.
 
    With  respect to the remaining  shares of Common Stock  subject to each such
option (i.e.,  those shares  with  respect to  which  the option  first  becomes
exercisable  before  or  after  1995),  each  optionee  was  granted  the right,
exercisable at any  time during  which such  option remains  outstanding and  is
exercisable  with respect  to such  shares, to  surrender for  cancellation that
portion of such option relating to 37.33 percent of such shares in return for  a
cash  payment from Ciba equal  to (A) the difference  between $117 per share and
the exercise price  per share of  such option  multiplied by (B)  the number  of
shares with respect to which such option is so surrendered and canceled.
 
    The grant of such rights, which were made with respect to 1,858,776 optioned
shares, was in addition to, and does not count against, the limits on the number
of  shares with respect to which other awards  under the Plan may be made to all
individuals and/or a single individual. All  payments in respect of such  rights
were  made by Ciba. The  Company has agreed that if  the payment under any right
would subject a recipient  to an excise tax  on excess parachute payments  under
Code  Section 4999  ("Section 4999"), the  Company would make  such further cash
payment to the recipient as would be necessary to provide the recipient with the
 
                                       35
<PAGE>
same after-tax amount that he or she would have received in the absence of  such
excise  tax. The  Company does  not believe that  any payments  under the rights
constitute excess parachute payments. However, because neither final regulations
nor other definitive guidance has been issued under Section 4999 relating to the
type of transaction that triggers the application of that provision and the type
and value of rights that constitute  excess parachute payments, there can be  no
assurance  that payments to  certain officers and  1-percent stockholders of the
Company will not constitute excess parachute payments.
 
NEW PLAN BENEFITS
 
    Since the performance units proposed provide various criteria from which the
Committee may choose to  determine awards, it is  not possible to determine  the
benefits  or  amounts that  will be  received,  or would  have been  received by
eligible individuals in the form of performance units.
 
    Since automatic  stock  option  grants to  new  non-employee  directors  are
potentially  pro rated, and since it is not possible to foresee when and whether
a non-employee director will be appointed or elected during the year, it is  not
possible  to determine the amount of awards eligible non-employee directors will
receive if the Plan is approved  by stockholders. For the Company's fiscal  year
January  1, 1995  through December  31, 1995,  the non-executive  directors as a
group received automatic stock options on 24,750 shares of Common Stock, with an
average exercise  price  of  $64.3674  per  share.  If  the  presently  proposed
amendment had been effective for such period, they would have received automatic
stock  options on 14,666 shares of Common  Stock, with an average exercise price
of $64.51  per share,  and automatic  share rights  to receive  5,142 shares  of
Company Common Stock.
 
    The  following  tables contain  information  for the  Company's  fiscal year
January 1, 1995 through December 31, 1995 about (i) stock options granted  under
the  Plan, and  (ii) special  cash rights  granted in  connection with  the Ciba
transaction to the named executive officers and directors and groups indicated.
 
                  STOCK OPTIONS GRANTED UNDER THE PLAN IN 1995
 
<TABLE>
<CAPTION>
                                                                                                AVERAGE EXERCISE
                                                                         NUMBER OF SHARES            PRICE
                          NAME AND POSITION                            SUBJECT TO OPTIONS(#)     OF OPTIONS ($)
- ---------------------------------------------------------------------  ---------------------  --------------------
<S>                                                                    <C>                    <C>
Edward E. Penhoet ...................................................            62,175            $  55.7210
  President and Chief Executive Officer
William J. Rutter ...................................................            62,175               55.7210
  Chairman
C. William Zadel ....................................................             5,037               51.1250
  Vice President and Chief Executive Officer,
  Ciba Corning Diagnostics Corp.
William G. Green ....................................................            29,475               54.3683
  Senior Vice President, Secretary and
  General Counsel
Dennis L. Winger ....................................................            28,675               54.1519
  Senior Vice President, Finance &
  Administration, and Chief Financial Officer
Current executive officers as a group ...............................           484,948               53.8437
  (21 persons)
Non-Executive Director Group ........................................            24,750               64.3674
  (8 persons)
All employees, including all current officers .......................         2,115,261               67.9554
  who are not executive officers, as a group
  (3993 employees)
</TABLE>
 
                                       36
<PAGE>
             SPECIAL CASH RIGHTS RELATED TO CIBA-GEIGY TRANSACTION
 
<TABLE>
<CAPTION>
                                                                                    AGGREGATE
                                                                                     DOLLAR            NUMBER
                              NAME AND POSITION                                   VALUE ($)(1)     OF RIGHTS(#)(2)
- ------------------------------------------------------------------------------  -----------------  ---------------
<S>                                                                             <C>                <C>
Edward E. Penhoet ............................................................    $   7,156,223           86,613
  President and Chief Executive Officer
William J. Rutter ............................................................        9,312,818          107,146
  Chairman
C. William Zadel .............................................................                0                0
  Vice President and Chief Executive Officer,
  Ciba Corning Diagnostics Corp.
William G. Green .............................................................        3,325,765           43,830
  Senior Vice President, Secretary and
  General Counsel
Dennis L. Winger .............................................................        3,762,567           45,522
  Senior Vice President, Finance &
  Administration, and Chief Financial Officer
Current executive officers as a group ........................................       40,587,683          522,292
  (21 persons)
Non-Executive Director Group .................................................        2,948,249           44,238
  (8 persons)
All employees, including current officers ....................................       78,585,810        1,292,246
  who are not executive officers,
  as a group (3993 persons)
</TABLE>
 
- ------------------------
(1) Based upon difference between $117 per share and exercise price of option to
    which each right relates.
 
(2) Of the  rights in  the table  granted to  the named  executive officers  and
    directors and groups indicated, the following number of rights at the dollar
    value  indicated applicable to options  which would first become exercisable
    in calendar  year  1995 do  not  require  that the  optionee  surrender  for
    cancellation  the portion of each option  underlying each such right: Edward
    E. Penhoet -- 19,501 rights ($1,422,029); William J. Rutter -- 19,501 rights
    ($1,422,029); William G. Green -- 8,687 rights ($611,812); Dennis L.  Winger
    --  3,008 rights ($146,819); current executive officers as a group -- 97,548
    rights  ($6,133,432);   non-executive  director   group  --   7,541   rights
    ($452,840);  all  employees,  including  all current  officers  who  are not
    executive officers, as a group -- 302,596 rights ($16,810,283).
 
AMENDMENT OR TERMINATION
 
    The Board may amend,  suspend or discontinue the  Plan at any time.  However
the  performance goals  established for Performance  Units may  not be modified.
Generally, the provisions  of the  Plan concerning automatic  option awards  may
only  be amended once every six months unless necessary to comply with the Code.
Without stockholder  approval,  the Board  may  not (1)  materially  modify  the
requirements  for  eligibility and  participation  in the  Plan,  (2) materially
increase the number of shares which may  be subject to awards granted under  the
Plan  (except as provided above),  or (3) make any  other change with respect to
which the Board determines that  stockholder approval is required by  applicable
law or regulatory standards.
 
    To  the extent not inconsistent  with the Plan, the  Committee may modify or
waive the terms of any outstanding award.
 
FEDERAL INCOME TAX CONSEQUENCES
 
    The following  is  a  general  description of  certain  federal  income  tax
consequences of the Plan. This description does not purport to be complete.
 
                                       37
<PAGE>
    The  Company will be entitled  to a business expense  deduction equal to the
ordinary income recognized by  an optionee on exercise  of an NSO. The  ordinary
income  recognized will be equal  to the excess of the  fair market value of the
purchased shares on the date of recognition over the exercise price.  Generally,
the  date of recognition will be the date  the option is exercised or, if later,
the first date shares acquired on exercise are not subject to a substantial risk
of forfeiture.
 
    The Company will also be entitled  to a business expense deduction equal  to
the   ordinary  income  recognized  by  an  optionee  due  to  a  "disqualifying
disposition" of stock acquired pursuant  to an ISO. A disqualifying  disposition
occurs  if an optionee disposes  of the acquired shares  within two years of the
date of the option grant, or within one year of the date the shares are acquired
by the optionee. In the case  of a disqualifying disposition, the optionee  will
generally  recognize ordinary  income in the  year of disposition,  in an amount
equal to the amount of ordinary  income the optionee would have recognized  from
the exercise of the option had the option been an NSO at the time of exercise.
 
    To  the extent that  the aggregate fair  market value (determined  as of the
respective date or dates of grant) of shares with respect to which options  that
would  otherwise be ISOs  are exercisable for  the first time  by any individual
during any  calendar year  exceeds the  sum of  $100,000, such  options will  be
treated  as NSOs. To the extent that an  option may be surrendered for a special
cash payment from Ciba, it will generally not qualify as an ISO.
 
    A recipient of restricted shares may be taxed in one of two ways. The  award
holder  either: (1) pays tax when the restrictions lapse, or (2) makes a special
election to pay tax in the  year the grant is made.  The value of the award  for
tax purposes is the fair market value of the shares at the applicable time, less
any  consideration paid by the award holder  for the shares. This value is taxed
as ordinary income. When the award holder  is taxed, the Company receives a  tax
deduction at the same time and for the same amount. If an award holder elects to
be  taxed at grant,  when the restrictions  lapse, there will  be no further tax
consequences attributable to the awarded  stock until sale or other  disposition
of the stock. However, dividends in cash and stock will be treated as follows:
 
        a.  if the above special tax election has been made, cash dividends paid
    to the award holder will be taxable dividend income to the award holder when
    paid,  but the Company will not  be entitled to any corresponding deduction;
    and
 
        b.  if  such election  has not  been made,  the award  holder will  have
    taxable  compensation income and the  Company a corresponding deduction when
    the dividends are paid.
 
    A recipient of share  rights paid in stock  recognizes no taxable income  at
the  time of grant.  However, when the  conditions precedent to  the issuance of
shares pursuant  to such  share rights  are satisfied,  the award  holder  would
recognize ordinary income equal to the fair market value on the date of issuance
of the shares less any consideration paid by the award holder. Any cash dividend
equivalent  paid to holders of share rights is ordinary income. The Company will
be entitled  to  a  deduction  equal  to  the  award  holder's  ordinary  income
recognized  pursuant  to the  issuance of  shares  under the  award in  the year
recognized by the award holder.
 
    A recipient of  a share unit  recognizes no  taxable income at  the time  of
grant.  Whether a  share unit is  paid in cash  or shares of  Company Stock, the
award holder will have ordinary income and the Company will have a corresponding
deduction when the award is paid. The measure of such income and deduction  will
be the fair market value of the shares at the time of payment.
 
    If  an award is accelerated as a result of a Corporate Transaction, all or a
portion of the value of  the award at that time  may be a parachute payment  for
purposes  of  the Internal  Revenue  Code's excess  parachute  provisions. Those
provisions generally provide that  if parachute payments  exceed three times  an
award  holder's  average  compensation  for the  five  tax  years  preceding the
Corporate Transaction,  the Company  loses its  deduction and  the recipient  is
subject  to a 20 percent excise tax for  the amount of the parachute payments in
excess of such average compensation.
 
                                       38
<PAGE>
    A special  cash payment  from Ciba  will constitute  taxable income  to  the
recipient  at the  time of  payment. The Company  believes that,  subject to the
limits of Section  162(m) of the  Internal Revenue Code  (applicable to  certain
officers  of the Company, as discussed below), the Company will be entitled to a
deduction for the amount of each such payment.
 
ACCOUNTING TREATMENT
 
    The following  is a  summary of  certain accounting  consequences of  awards
under  generally accepted accounting principles.  In October 1995, the Financial
Accounting Standards Board  issued Statement of  Financial Accounting  Standards
No.  123,  "Accounting  for  Stock-Based  Compensation"  ("FAS  No.  123"). This
standard defines  a  fair  value  based method  of  accounting  for  stock-based
employee  compensation plans; however,  it also allows an  entity to continue to
measure compensation cost for  those plans using the  provisions of APB  Opinion
No.  25, "Accounting  for Stock Issued  to Employees" ("Opinion  25"). Under the
fair value based method, compensation cost  is measured at the grant date  based
on  the fair value of the award and is recognized over the service period, which
is usually the vesting period. Under Opinion 25, compensation cost is recognized
based on the difference, if any, between  the market price of the stock and  the
amount  an employee must  pay to acquire  the stock. The  Company has elected to
continue  accounting  for  compensation   cost  arising  from  its   stock-based
compensation  plans under the Opinion  25 approach, which serves  as a basis for
the following description.
 
    An option granted with an exercise price less than the fair market value  of
the  option shares on the  date of grant will  give rise to compensation expense
equal to the difference between the fair market value of the shares on the  date
of  grant and the  exercise price. The  expense will be  accrued as the optionee
vests in the option or the shares purchasable under the option. Option grants at
100 percent of fair market value will not result in any charge to the  Company's
earnings.
 
    The  grant  of restricted  stock or  share rights  will generally  result in
compensation expense  equal to  the market  value of  the underlying  shares  of
Common  Stock on the date of grant  (less any consideration paid therefor). This
expense will generally be amortized over the term of the vesting in such awards,
but the expense may be subject  to periodic adjustment depending on  performance
criteria  and other  factors. In the  case of certain  performance criteria, the
recognition and measurement of the expense may be delayed until the  performance
criteria are attained or are likely to be attained.
 
    Generally,  the fair market value of a share unit on the date of grant (less
any consideration paid therefor) will be accrued  as an expense and, at the  end
of  each fiscal quarter thereafter, the amount (if any) by which the fair market
value of the unit has increased or decreased from the amount previously  accrued
will  be  recorded as  an adjustment  to  compensation expense.  In the  case of
certain vesting or  performance criteria, the  expense may be  amortized or  the
recognition  and measurement of the expense may be delayed until the performance
criteria are attained or are likely to be attained.
 
    The number of outstanding options, restricted stock and share rights will be
a factor in determining earnings per share on a fully diluted basis.
 
    For fiscal years beginning with the Company's 1996 fiscal year, FAS No.  123
requires  the  Company  to disclose,  in  footnotes to  the  Company's financial
statements, the impact  that options  and other  awards granted  under the  Plan
would  have had on the Company's reported  earnings were the fair value of those
awards treated as compensation expense.
 
DEDUCTION LIMIT FOR EXECUTIVE COMPENSATION
 
    Recently enacted Section 162(m) of the Internal Revenue Code limits  federal
income  tax deductions for  compensation paid after 1993  to the chief executive
officer and the four other most highly compensated officers of a public  company
to  $1  million  per  year,  but  contains  an  exception  for performance-based
compensation that satisfies certain conditions.
 
    The Company believes that  stock options granted to  its executives with  an
exercise price equal to or greater than the fair market value of Common Stock on
the  date  of grant,  and  performance units  described  in this  proposal, will
qualify for the performance-based compensation exception to the deduction limit,
assuming that the Amended Plan is approved by stockholders.
 
                                       39
<PAGE>
    The cash  payments made  by Ciba  will  not be  exempt from  application  of
Section  162(m). As a  result, if the amount  of any such payment  to any of the
five executive officers of the Company  subject to Section 162(m) in any  fiscal
year,  together with other compensation paid to such officer in such fiscal year
that is not exempt from the  limitations of Section 162(m), exceeds $1  million,
the Company will not be entitled to a deduction for the amount of such excess.
 
VOTE REQUIRED FOR APPROVAL OF THE AMENDED CHIRON 1991 STOCK OPTION PLAN
 
    The  affirmative vote  of a  majority of the  shares of  Common Stock having
voting power present in person or represented by proxy, a quorum being  present,
is necessary to approve the Amended Plan.
 
    THE  BOARD OF DIRECTORS RECOMMENDS  A VOTE FOR THE  PROPOSED AMENDED PLAN TO
CHANGE THE FORMULA FOR GRANTING  AUTOMATIC ANNUAL STOCK OPTIONS TO  NON-EMPLOYEE
DIRECTORS,  TO ADD  AN ANNUAL GRANT  OF AUTOMATIC SHARE  RIGHTS FOR NON-EMPLOYEE
DIRECTORS, AND  TO ADD  PERFORMANCE UNITS,  WHICH ARE  RESTRICTED SHARES,  SHARE
RIGHTS  AND SHARE UNITS AWARDED TO CORPORATE VICE-PRESIDENTS AND OTHER EXECUTIVE
OFFICERS WHICH COMPLY  WITH THE  REQUIREMENTS OF INTERNAL  REVENUE CODE  SECTION
162(m).
 
                                  PROPOSAL 4:
          RATIFICATION OF SELECTION OF INDEPENDENT PUBLIC ACCOUNTANTS
 
    The  Board  of Directors  has selected  KPMG  Peat Marwick  LLP to  serve as
independent  public  accountants  for  Chiron  for  the  current  fiscal   year.
Ratification  by the stockholders will be sought  for the selection by the Board
of Directors of KPMG Peat Marwick LLP as independent public accountants to audit
the accounts and records of Chiron for the fiscal year ending December 31, 1996,
and to perform other appropriate services. Representatives of KPMG Peat  Marwick
LLP  are expected to be present at  the Annual Meeting to respond to appropriate
questions and to make a statement if the representatives so desire. In the event
that a majority of the  shares voting on the matter  at the Annual Meeting  does
not  vote for ratification of the selection  of KPMG Peat Marwick LLP, the Board
of Directors will reconsider such selection. Even if the selection is  ratified,
the  Board  of Directors  in  its discretion  may  direct the  appointment  of a
different independent accounting firm at any  time during the year if the  Board
determines that such a change would be in the best interest of the Company.
 
    On  March 7, 1994, the Finance and Audit Committee of the Company's Board of
Directors, by  delegated  authority of  the  Board of  Directors,  approved  the
engagement  of the  independent certified  public accounting  firm of  KPMG Peat
Marwick LLP to audit  the consolidated financial statements  of the Company  for
the  year ended December 31, 1994. Accordingly,  the engagement of Ernst & Young
LLP as  the  Company's  independent auditors  was  discontinued  effective  upon
conclusion  of the audit of the  Company's consolidated financial statements for
the year  ended December  31,  1993. The  audit  of the  Company's  consolidated
financial  statements  for the  year ended  December 31,  1993 was  completed on
February 25, 1994.
 
    The reports of  Ernst & Young  LLP on the  Company's consolidated  financial
statements  for each of  the two fiscal  years in the  period ended December 31,
1993 did not contain an adverse opinion or a disclaimer of opinion and were  not
qualified or modified as to uncertainty, audit scope or accounting principles.
 
    In  connection  with  the  audits of  the  Company's  consolidated financial
statements for each of the  two fiscal years ended  December 31, 1992 and  1993,
and  the  subsequent  interim period  prior  to  March 7,  1994,  there  were no
disagreements between  the Company  and Ernst  &  Young LLP  on any  matters  of
accounting  principles or practices, financial statement disclosure, or auditing
scope and procedures which, if not resolved to the satisfaction of Ernst & Young
LLP, would have  caused Ernst &  Young LLP to  make reference to  the matter  in
their reports.
 
    There  were  no  reportable  events  (as  defined  in  Regulation  S-K  Item
304(a)(1)(v)) during the two fiscal years ended December 31, 1992 and 1993,  and
the subsequent interim period prior to March 7, 1994.
 
    The  Company did not consult with KPMG Peat Marwick LLP during the two years
or subsequent interim period prior to  March 7, 1994, on either the  application
of accounting principles or type of opinion KPMG Peat Marwick LLP might issue on
the Company's financial statements.
 
                                       40
<PAGE>
    THE  BOARD OF DIRECTORS  RECOMMENDS A VOTE  FOR THE PROPOSAL  TO RATIFY KPMG
PEAT MARWICK LLP AS INDEPENDENT PUBLIC ACCOUNTANTS OF THE COMPANY FOR THE FISCAL
YEAR ENDING DECEMBER 31, 1996.
 
    The affirmative vote of the holders of a majority of the shares  represented
and  voting on the matter will be required  to ratify the selection of KPMG Peat
Marwick LLP.
 
                         COMPLIANCE WITH SECTION 16(a)
                     OF THE SECURITIES EXCHANGE ACT OF 1934
 
    Section 16(a)  of  the Exchange  Act  requires the  Company's  officers  and
directors, and persons who own more than 10 percent of a registered class of the
Company's  equity  securities,  to  file reports  of  ownership  and  changes in
ownership on  Forms 3,  4 and  5 with  the Securities  and Exchange  Commission.
Officers,  directors and  greater than 10  percent stockholders  are required by
Securities and Exchange Commission regulation to furnish the Company with copies
of all Forms 3, 4 and 5 they file.
 
    Based solely on  the Company's review  of the  copies of such  forms it  has
received  and written representations  from certain reporting  persons that they
were not required to  file Forms 5  for fiscal year  1995, the Company  believes
that  all  its  officers and  directors  complied with  all  filing requirements
applicable to them with respect to  transactions during fiscal year 1995  except
that  Dr. Amelio filed late a Form 4  to reflect the sale, on September 8, 1995,
of 124 shares of Chiron  Common Stock and Dr.  Gerber, after termination of  his
status  as a Company  officer, filed late a  Form 4 to  reflect his exercise and
subsequent sale of 9,046 shares of Chiron Common Stock underlying such options.
 
                             STOCKHOLDER PROPOSALS
 
    Stockholder proposals  intended  to  be  considered  for  inclusion  in  the
Company's Proxy Statement for next year's Annual Meeting of Stockholders must be
received  at the Company's principal executive office by December 20, 1996. Such
proposals may be  included in next  year's Proxy Statement  if they comply  with
certain  rules  and  regulations  promulgated  by  the  Securities  and Exchange
Commission.
 
                                 OTHER BUSINESS
 
    The Board  of  Directors is  not  aware of  any  other matter  that  may  be
presented  for action at the Annual Meeting. Should any other matter requiring a
vote of the stockholders arise, the  enclosed proxy card gives authority to  the
persons  listed on the card to vote at  their discretion in the best interest of
the Company.
 
                     ANNUAL REPORT AND FINANCIAL STATEMENTS
 
    The  Company  has  chosen  again  this  year  to  print  summary   financial
information  for the  fiscal year  ended December  31, 1995  in its  1995 Annual
Report, a copy of which is enclosed  with this proxy material. The full  audited
consolidated  financial statements of the Company and its subsidiaries and other
required financial disclosures  appear in  a brochure enclosed  inside the  back
cover of the Annual Report.
 
Dated: April 11, 1996                     BY ORDER OF THE BOARD OF DIRECTORS
 
                                          WILLIAM G. GREEN
 
                                          William G. Green,
                                            SECRETARY
 
                                       41
<PAGE>
                                                                         ANNEX 1
 
    AMENDMENT TO RESTATED CERTIFICATE OF INCORPORATION OF CHIRON CORPORATION
 
    Article  FIFTH of  the Restated Certificate  of Incorporation  is amended to
read in full as follows:
 
    FIFTH: This corporation is authorized to  issue two classes of shares to  be
designated, respectively, "Preferred Stock" and "common stock." The total number
of  shares which this  corporation is authorized  to issue is  five hundred five
million (505,000,000). Five million (5,000,000) shares shall be Preferred  Stock
and  five  hundred  million  (500,000,000) shares  shall  be  common  stock. The
Preferred Stock shall  have a par  value of  $0.01 per share;  the common  stock
shall have a par value of $0.01 per share.
 
1.  PREFERRED STOCK.
 
    The  Preferred Stock may be issued from time  to time in one or more series.
The Board of Directors is expressly authorized, in the resolution or resolutions
providing for the  issuance of any  wholly unissued series  Preferred Stock,  to
fix,   state  and   express  the  powers,   rights,  designations,  preferences,
qualifications,  limitations   and  restrictions   thereof,  including   without
limitation: the rate of dividends upon which and the times at which dividends of
shares  of such series shall  be payable and the  preference, if any, which such
dividends shall  have relative  to dividends  on shares  of any  other class  or
classes  or any other series of stock of the corporation; whether such dividends
shall be cumulative or noncumulative, and if cumulative, the date or dates  from
which dividends on shares of such series shall be cumulative; the voting rights,
if  any, to be provided for shares of such series; the rights, if any, which the
holders of shares of  such series shall  have in the event  of any voluntary  or
involuntary  liquidation,  dissolution  or  winding up  of  the  affairs  of the
corporation; the rights,  if any,  which the holders  of shares  of such  series
shall  have to convert  such shares into  or exchange such  shares for shares of
stock of the corporation, and the terms and conditions, including price and rate
of exchange of such conversion or exchange; and the redemption rights (including
sinking fund provisions),  if any,  for shares of  such series;  and such  other
powers,  rights,  designations,  preferences,  qualifications,  limitations  and
restrictions as  the Board  of Directors  may desire  to so  fix. The  Board  of
Directors  is also expressly authorized to fix the number of shares constituting
such series and to increase or decrease the number of shares of any series prior
to the issuance of shares of that series and to increase or decrease the  number
of shares of any series subsequent to the issuance of shares of that series, but
not  to decrease such number below the number of shares outstanding. In case the
number of shares of  any series shall be  so decreased, the shares  constituting
such  decrease shall resume the  status which they had  prior to the adoption of
the resolution originally fixing the number of shares of such series.
 
2.  COMMON STOCK.
 
    The common stock may be issued from time to time in one or more series. Four
hundred ninety-nine million five hundred thousand (499,500,000) shares of common
stock are designated  "Common Stock."  All other  series of  common stock  shall
collectively  consist of  five hundred  thousand (500,000)  shares and  shall be
designated, as a group, "Restricted Common Stock."
 
3.  RESTRICTED COMMON STOCK.
 
    (a)  AUTHORITY OF BOARD TO FIX RIGHTS OF RESTRICTED COMMON STOCK.  The Board
of Directors is expressly authorized, in the resolution or resolutions providing
for the issuance of  any wholly unissued series  of Restricted Common Stock,  to
fix,  state and  express, within the  limits expressed  hereinbelow, the powers,
designations, preferences and  rights of  the Restricted Common  Stock, and  the
qualifications,  limitations or restrictions thereof.  The Board of Directors is
also expressly authorized to fix the  number of shares constituting such  series
and  to increase  or decrease the  number of shares  of any series  prior to the
issuance of shares  of that series  and to  increase or decrease  the number  of
shares  of any series subsequent to the issue  of shares of that series, but not
to decrease such  number below the  number of such  series then outstanding.  In
case  the  number of  shares of  any series  shall be  so decreased,  the shares
constituting such decrease shall resume the  status which they had prior to  the
adoption  of  the resolution  originally  fixing the  number  of shares  of such
series.
 
                                      A-1
<PAGE>
    (b)  SPECIFIC RIGHTS.  The rights, preferences, privileges and  restrictions
of  the  Common Stock  and Restricted  Common  Stock shall  be identical  in all
respects, except as follows, or, for  the Restricted Common Stock, as fixed  and
determined by the Board of Directors within the limitations which follow:
 
         i)  CONVERSION RIGHTS.  The Restricted  Common Stock may be convertible
    into or exchangeable for Common Stock, at a conversion or exchange ratio  of
    not  more than one share of Common Stock for each share of Restricted Common
    Stock and upon such other terms and conditions as the Board of Directors may
    establish.
 
         ii) VOTING RIGHTS.   Subject to the special  voting rights (if any)  of
    the  Preferred Stock  set forth  or determined  as provided  in this Article
    FIFTH, each holder of Common Stock of this corporation shall be entitled  to
    one vote for each share of such stock outstanding in the name of such holder
    on  the books  of this  corporation on  the record  date designated  for the
    purpose of such  vote, and  each holder of  Restricted Common  Stock of  the
    corporation  shall be  entitled, for  each share  of such  Restricted Common
    Stock outstanding in the name of such holder on the books of the corporation
    on the record date designated for the purpose of such vote, to the number of
    votes as has been fixed by the Board of Directors, but the vote per share of
    Restricted Common Stock shall not be more than the proportionate vote of the
    Common Stock  into which  such  Restricted Common  Stock is  convertible  or
    exchangeable.
 
        iii)  DIVIDEND RIGHTS.   Subject  to the  prior rights  (if any)  of the
    holders of the Preferred Stock as  to dividends, the holders of  outstanding
    shares  of Common  Stock and  Restricted Common  Stock shall  be entitled to
    receive, when and as declared by the  Board of Directors, out of the  assets
    of  the corporation at the time legally available therefor, dividends at the
    rate determined  by the  Board  of Directors;  provided, however,  that  the
    dividend  on each share  of Restricted Common  Stock shall be  less than the
    proportionate dividend  on each  share  of Common  Stock  into which  it  is
    convertible or exchangeable.
 
        iv) LIQUIDATION RIGHTS.  In the event of any liquidation, dissolution or
    winding  up  of this  corporation either  voluntarily or  involuntarily, but
    subject to the liquidation preference (if  any) of the holders of  Preferred
    Stock  by reason of their ownership thereof, the holders of Common Stock and
    Restricted Common Stock shall be entitled to receive pro rata the  remaining
    assets  of the corporation available for distribution to shareholders except
    that the amount per  share paid in liquidation  on each share of  Restricted
    Common  Stock shall be less than the  proportionate amount per share paid on
    each share of the Common Stock into which it is convertible or exchangeable.
 
         v)  ADJUSTMENTS.    The  Board  of  Directors  shall  make  appropriate
    adjustments  to the conversion or exchange ratio and to the voting, dividend
    and liquidation rights of  the Restricted Common Stock  in the event of  any
    stock  split, stock dividend or similar  transaction affecting the number of
    outstanding shares of Common  Stock or Restricted  Common Stock without  the
    corporation's receipt of consideration thereof.
 
                                      A-2
<PAGE>
                                                                         ANNEX 2
                         CHIRON 1991 STOCK OPTION PLAN
  [AS AMENDED AUGUST 14, 1993, APRIL 11, 1994, FEBRUARY 24, 1995 AND MARCH 8,
                                     1996]
 
I.  PURPOSES
 
    This  Chiron 1991  Stock Option Plan  ("Plan") is intended  to enable Chiron
Corporation ("Corporation") to attract and  retain the following individuals  by
offering them incentives and rewards, in the form of options, restricted shares,
share  rights, share units and performance units ("awards") which will encourage
them to acquire a  proprietary interest in the  Corporation, to continue in  the
service  of the  Corporation or  its subsidiaries,  and to  provide incentive to
build value for stockholders: (a)  employees (including officers and  directors)
of  the Corporation and its subsidiaries,  (b) non-employee members of the Board
of Directors of the Corporation  ("Board"), and (c) consultants and  independent
contractors   who  perform  valuable  services   for  the  Corporation  and  its
subsidiaries.
 
    In addition, the Plan is intended  to permit the Corporation to satisfy  its
obligations  in connection with options it will  assume pursuant to the terms of
the Agreement and  Plan of Merger  dated as of  July 21, 1991  by and among  the
Corporation,   Chiron  Acquisition  Subsidiary,   Inc.,  and  Cetus  Corporation
("Agreement"). Upon consummation of the transactions described in the  Agreement
("Merger"),  the Plan  will supersede  Cetus Corporation's  Amended and Restated
Common Stock Option Plan and  Cetus Corporation's Non-Employee Directors'  Stock
Option  Plan ("Cetus  Prior Plans"). Upon  stockholder approval,  this Plan will
also supersede the  following Chiron  prior plans: the  Protos Corporation  1988
Stock  Option  Plan  (upon  the  merger  of  Protos  into  Chiron),  the  Chiron
Ophthalmics, Inc. 1986 Stock Option Plan (upon the merger of Chiron  Ophthalmics
into  a wholly owned subsidiary of  Chiron), the Corporation's 1982 Stock Option
Plan and the Corporation's 1984  Non-Qualified Stock Option Plan  (collectively,
"Chiron Prior Plans").
 
II.  ADMINISTRATION
 
    The  Plan will be administered by a committee or committees appointed by the
Board and consisting of one or more members of the Board. The Board may delegate
the responsibility for  administration of  the Plan with  respect to  designated
classes of award holders to different committees, subject to such limitations as
the  Board deems appropriate. With respect  to any matter, the term "Committee,"
when used in  this Plan, will  refer to  the committee that  has been  delegated
authority  with respect to  such matter. Members  of a committee  will serve for
such term as  the Board may  determine, and will  be subject to  removal by  the
Board at any time.
 
    (a)   16(b)  The composition of any committee responsible for administration
of the  Plan with  respect  to award  holders who  are  subject to  the  trading
restrictions  of Section  16(b) of  the Securities  Exchange Act  of 1934 ("1934
Act") with  respect  to securities  of  the  Corporation will  comply  with  the
applicable requirements of Rule 16b-3 of the Securities and Exchange Commission.
 
    (b)   162(m)  The composition of any committee responsible for establishing,
administering, and certifying  performance goals  for awards  granted under  the
Plan  that are  intended to comply  with Internal Revenue  Code ("Code") Section
162(m) ("performance units")  will comply  with the  applicable requirements  of
Code Section 162(m) and the regulations promulgated thereunder.
 
    (c)    AUTHORITY.   Any  committee appointed  by  the Board  will  have full
authority  to  administer   the  Plan   within  the  scope   of  its   delegated
responsibilities,  including authority  to interpret  and construe  any relevant
provision of  the Plan,  to adopt  such rules  and regulations  as it  may  deem
necessary,  and to determine the  terms and conditions of  awards made under the
Plan (which need  not be identical).  Decisions of a  committee made within  the
discretion delegated to it by the Board will be final and binding on all persons
who have an interest in the Plan.
 
                                      A-3
<PAGE>
III.  ELIGIBILITY FOR AWARDS
 
    (a)   DISCRETIONARY  AWARDS.  From  time to  time the Committee  may, in its
discretion, select individuals  from among the  following categories to  receive
awards under the Plan:
 
        (1)   EMPLOYEES.  The Committee  may select employees of the Corporation
    or its  subsidiaries  (including officers,  whether  or not  they  are  also
    members of the Board).
 
        (2)   CONSULTANTS AND INDEPENDENT CONTRACTORS.  The Committee may select
    consultants and independent  contractors whose services  tend to  contribute
    materially  to the success  of the Corporation or  its subsidiaries or whose
    services may reasonably be anticipated to so contribute.
 
    (b)   PERFORMANCE  UNITS.   Corporate  vice-presidents and  other  executive
officers  ("162(m) executives") will be eligible to receive performance units in
addition to, or in lieu of, other discretionary awards granted under the Plan.
 
    (c)  AUTOMATIC GRANTS.   Members of the Board who  are not employees of  the
Corporation or its subsidiaries will receive awards in accordance with, and only
in accordance with, the Plan's automatic award provisions.
 
    (d)    SUBSTITUTE OPTIONS.   Upon  consummation  of the  Merger, outstanding
options  under  the   Cetus  Prior  Plans   (including  related  Limited   Stock
Appreciation  Rights) will be converted, in the manner and at the exchange ratio
specified in the Agreement, into substitute  options under this Plan to  acquire
Common  Stock (as defined below). Upon  stockholder approval and, with regard to
the Protos prior  plan options and  the Chiron Ophthalmics  prior plan  options,
consummation of the relevant mergers, outstanding options under the Chiron Prior
Plans  will  be  converted into  options  under  this Plan.  These  options will
preserve the exercise price of the outstanding options as adjusted, in the  case
of  options under the Protos  Corporation 1988 Stock Option  Plan and the Chiron
Ophthalmics, Inc. 1986 Stock Option Plan, to reflect the substitution of  Common
Stock.  These options will also  preserve the other terms  and conditions of the
outstanding options; provided, however, that on the Effective Date of this Plan,
outstanding automatic option  grants under the  Corporation's 1982 Stock  Option
Plan  will be conformed, other than to  extend the term, to the Automatic Option
Grants under this Plan. Collectively, these options will be known as "Substitute
Options."
 
IV.  STOCK SUBJECT TO THE PLAN
 
    (a)   CLASS.   The  stock  subject  to awards  under  the Plan  is  (i)  the
Corporation's  authorized  but  unissued  or  reacquired  Common  Stock ("Common
Stock"), or (ii) shares  of one or more  series of the Corporation's  authorized
but  unissued or reacquired Restricted Common  Stock, in the aggregate, "Company
Stock." In connection with the grant  of awards under the Plan, the  Corporation
may repurchase shares in the open market or otherwise.
 
    (b)  AGGREGATE AMOUNT
 
        (1)   SHARES.  Subject to  adjustment under Sections IV(c) and IV(b)(3),
    the aggregate maximum number of shares of Company Stock that may be  subject
    to  awards under the Plan is 4,500,000  plus the number of shares of Company
    Stock remaining for issuance  on the Effective Date  of this Plan under  the
    Corporation's   1982   Stock  Option   Plan   and  the   Corporation's  1984
    Non-Qualified Stock  Option  Plan.  Notwithstanding  the  foregoing,  as  of
    January  1 of each fiscal year after 1991, the aggregate number of shares of
    Company Stock that may be subject to awards under the Plan will be increased
    by 1.50% of the number of Chiron Common Equivalent Shares outstanding as  of
    December  31 of the preceding  fiscal year. The maximum  number of shares of
    Company Stock with respect  to which awards may  be granted to any  employee
    during the term of the Plan is 1,000,000 shares. Subject to adjustment under
    Sections IV(c) and IV(b)(3), not more than 4,500,000 shares of Company Stock
    plus  the number of  shares of Company  Stock remaining for  issuance on the
    Effective Date of this Plan under  the Corporation's 1982 Stock Option  Plan
    and the Corporation's 1984 Non-Qualified Stock Option Plan may be subject to
    Incentive  Options  (as  defined below)  granted  under the  Plan  after the
    Effective Date. "Chiron Common  Equivalent Shares" are  the total number  of
    outstanding shares of Common Stock plus the total
 
                                      A-4
<PAGE>
    number  of shares  of Common Stock  issuable upon conversion  or exercise of
    outstanding warrants, options and convertible  securities. In no event  will
    more  than 500,000  shares of Restricted  Common Stock, whether  in a single
    series or in multiple series, be subject to award under the Plan.
 
        (2)  RESTRICTED COMMON STOCK.  Shares of Restricted Common Stock may  be
    issued  under  the  Plan  in  one  or  more  separate  series.  The  rights,
    preferences and privileges, together  with the restrictions and  limitations
    and the number of shares, of each series of Restricted Common Stock issuable
    under  the  Plan  will be  set  forth  in the  Corporation's  Certificate of
    Determination of Preferences  of Common Stock  ("Certificate") as in  effect
    from  time to  time during the  term of the  Plan. Shares of  each series of
    Restricted Common Stock will be  convertible or exchangeable into shares  of
    Common  Stock in accordance with the terms and provisions of the Certificate
    applicable to that series.
 
        (3)  REUSE OF SHARES.  If any outstanding option under the Chiron  Prior
    Plans, the Cetus Prior Plans or this Plan (including the Substitute Options)
    expires  or is terminated or canceled  for any reason (including pursuant to
    Section X of the Plan but other than pursuant to surrender of the option for
    a cash payment  in accordance with  Section XIII of  the Plan) before  being
    exercised for the full number of shares to which it applies, then the shares
    allocable  to the  unexercised portion  of such  option will  not be charged
    against the limitations of  Section IV(b)(1) and  will become available  for
    subsequent  grants under the Plan. To the extent that a share right or share
    unit expires or is  terminated, or is canceled  or forfeited for any  reason
    without  being paid in cash or shares of Company Stock, any remaining shares
    allocable to the unpaid portion of such share right or share unit shall  not
    be  charged  against the  limitations of  Section  IV(b)(1) and  will become
    available again for subsequent grants under the Plan. Shares subject to  any
    option or portion of an option surrendered in accordance with the "Surrender
    of  Options for Cash or  Stock" provisions of this  Plan, shares for which a
    cash payment is made in lieu thereof under a restricted share, share unit or
    share right,  and shares  forfeited  to or  repurchased by  the  Corporation
    pursuant to its forfeiture and repurchase rights under this Plan will not be
    available for subsequent awards under the Plan.
 
    (c)   ADJUSTMENTS.   In the  event any change  is made to  the Company Stock
subject to the Plan (whether by reason of merger, consolidation, reorganization,
recapitalization, stock dividend, stock  split, combination of shares,  exchange
of shares, or other change in corporate or capital structure of the Corporation)
then, unless such change results in the termination of all awards, the Committee
will  make  appropriate adjustments  to the  kind and  maximum number  of shares
subject to the Plan, the kind and maximum number of shares for which options are
to be granted to non-employee directors, and the kind and number of shares  and,
where applicable, price per share of stock subject to outstanding awards.
 
V.  TERMS AND CONDITIONS OF OPTIONS
 
    Stock  options granted under the Plan may, in the Committee's discretion, be
either incentive stock  options ("Incentive Options")  qualifying under  Section
422  of the Internal Revenue Code of 1986, as amended ("Internal Revenue Code"),
or nonstatutory options. Individuals who are not employees of the Corporation or
its subsidiaries  may only  be  granted nonstatutory  options. Options  will  be
evidenced  by instruments in  such form as  the Committee may  from time to time
approve. These instruments will  conform to the  following terms and  conditions
and,  in  the  discretion  of  the  Committee,  may  contain  such  other terms,
conditions and restrictions as are not inconsistent with the following:
 
    (a)   OPTION PRICE.    The option  price  per share  will  be fixed  by  the
Committee,  but  in  no event  will  the option  price  per share  be  less than
eighty-five percent (85%) of the Fair Market  Value of the option shares on  the
date  of the option grant;  provided, however, that in  no event will the option
price per share of an Incentive Option  be less than one hundred percent  (100%)
of  the Fair Market Value of the option  shares on the date of the option grant.
Notwithstanding the foregoing, Substitute Options will have an option price  per
share determined pursuant to Section III(d) of this Plan.
 
                                      A-5
<PAGE>
    (b)  NUMBER OF SHARES, TERM AND EXERCISE
 
        (1)    TERM AND  NUMBER.   Each option  granted under  the Plan  will be
    exercisable on such date or dates,  during such period, and for such  number
    of shares of Company Stock as the Committee determines and sets forth in the
    instrument evidencing the option. No option granted under the Plan will have
    an  expiration date that is more than 10  years after the date of the option
    grant.
 
        (2)   EXERCISE.    After  any option  granted  under  the  Plan  becomes
    exercisable,  it may be exercised  by notice to the  Corporation at any time
    prior to  the  termination of  such  option.  Except as  authorized  by  the
    Committee  in accordance with Section VIII,  the option price for the number
    of shares for which the option is exercised will become due and payable upon
    exercise.
 
        (3)   PAYMENT.   The  option  price will  be  payable in  full  in  cash
    (including  cash equivalents);  provided, however,  that the  Committee may,
    either at the time the option is granted or at the time it is exercised  and
    subject to such limitations as it may determine, authorize payment of all or
    a  portion of  the option  price in  one or  a combination  of the following
    alternative forms:
 
            (i) a promissory note authorized pursuant to Section VIII;
 
           (ii) full payment in shares of Common Stock valued as of the exercise
       date and  held  for  the  requisite  period to  avoid  a  charge  to  the
       Corporation's earnings; or
 
          (iii) by delivery of a properly executed exercise notice together with
       irrevocable   instructions  to  a  broker  to  promptly  deliver  to  the
       Corporation the amount of sale or loan proceeds to pay the option price.
 
    (c)  TERMINATION OF SERVICES.  The Committee will determine and set forth in
each option whether the  option will continue to  be exercisable, and the  terms
and  conditions of such exercise, on and  after the date that an optionee ceases
to  be  employed  by,  or  to  provide  services  to,  the  Corporation  or  its
subsidiaries.  The date of  termination of an  optionee's employment or services
will be determined by the Committee, which determination will be final.
 
    (d)  INCENTIVE OPTIONS.  Options granted under the Plan that are intended to
be Incentive  Options will  be subject  to the  following additional  terms  and
conditions:
 
        (1)   DOLLAR LIMITATION.   To the extent that  the aggregate Fair Market
    Value (determined as  of the respective  date or dates  of grant) of  shares
    with  respect to which  options that are  granted after 1986  and that would
    otherwise be Incentive  Options are exercisable  for the first  time by  any
    individual during any calendar year under the Plan (or any other plan of the
    Corporation,  a  parent or  subsidiary  corporation or  predecessor thereof)
    exceeds the sum  of $100,000  (or such greater  amount as  may be  permitted
    under  the  Internal Revenue  Code), whether  by  reason of  acceleration or
    otherwise, such options will not be treated as Incentive Options. In  making
    such  a determination, options  will be taken  into account in  the order in
    which they  were  granted.  The  aggregate Fair  Market  Value  (as  of  the
    respective  date or dates of grant) of  shares of the Corporation (or parent
    or subsidiary corporation) for which  Incentive Options could be granted  to
    any  one individual in a  single calendar year before  1987 could not exceed
    $100,000 at the time of grant,  plus unused carryovers from the  immediately
    preceding three calendar years.
 
        (2)  10% STOCKHOLDER.  If any employee to whom an Incentive Option is to
    be  granted pursuant to the provisions of the Plan is, on the date of grant,
    the owner of stock (determined with application of the ownership attribution
    rules of Section 424(d) of the  Internal Revenue Code) possessing more  than
    ten percent (10%) of the total combined voting power of all classes of stock
    of  his  or  her  employer  corporation  or  of  its  parent  or  subsidiary
    corporation ("10% Stockholder"), then the following special provisions  will
    apply to the option granted to such individual:
 
           (i) The option price per share of the stock subject to such Incentive
       Option  will not be less than one  hundred ten percent (110%) of the Fair
       Market Value of the option shares on the date of grant; and
 
                                      A-6
<PAGE>
           (ii) The option will not have a term in excess of five (5) years from
       the date of grant.
 
        (3)  SEQUENTIAL EXERCISE.  No Incentive Option granted before January 1,
    1987 may be exercised  while there remains  outstanding any other  Incentive
    Option  to purchase shares  of the Corporation (or  its parent or subsidiary
    corporation) which was granted at an earlier date to the optionee.
 
        (4)  PARENT AND SUBSIDIARY.   For purposes of this Section V(d)  "parent
    corporation"  and "subsidiary corporation" will  have the meaning attributed
    to those terms, as they are used  in Section 422(b) of the Internal  Revenue
    Code.
 
    (e)  WITHHOLDING
 
        (1)    OBLIGATION.    The  Corporation's  obligation  to  deliver  stock
    certificates upon the exercise  of an option will  be subject to the  option
    holder's  satisfaction of all applicable federal, state and local income and
    employment tax withholding requirements.
 
        (2)  PAYMENT.  In the event that an option holder is required to pay  to
    the  Corporation  an  amount  with  respect  to  income  and  employment tax
    withholding obligations  in  connection  with exercise  of  an  option,  the
    Committee  may, in its discretion and  subject to such limitations and rules
    as it may  adopt, permit  the option holder  to satisfy  the obligation,  in
    whole  or in part, by delivering shares  of Common Stock already held by the
    option holder or  by making an  irrevocable election that  a portion of  the
    total  value of the shares subject to the option be paid in the form of cash
    in lieu of  the issuance of  Company Stock,  and that such  cash payment  be
    applied to the satisfaction of the withholding obligations.
 
VI.  RESTRICTED SHARES, SHARE RIGHTS AND SHARE UNITS
 
    (a)  NATURE OF AWARDS
 
        (1)  RESTRICTED SHARES.  A restricted share granted under the Plan shall
    consist  of shares of Company Stock, the  retention and transfer of which is
    subject to  such  terms,  conditions  and  restrictions  (whether  based  on
    performance  standards  or periods  of  service or  otherwise  and including
    repurchase and/or  forfeiture rights  in favor  of the  Corporation) as  the
    Committee  shall determine. The terms,  conditions and restrictions to which
    restricted shares are subject shall be evidenced by instruments in such form
    as the Committee may from  time to time approve and  may vary from grant  to
    grant. The Committee shall have the absolute discretion to determine whether
    any consideration (other than the services of the potential award holder) is
    to  be  received  by the  Corporation  or  its subsidiaries  as  a condition
    precedent to the issuance of restricted shares.
 
        (2)  SHARE RIGHTS.  A share  right granted under the Plan shall  consist
    of  the right, subject  to such terms,  conditions and restrictions (whether
    based on  performance standards  or  periods of  service or  otherwise),  to
    receive a share of Company Stock (together with cash dividend equivalents if
    so  determined by the Committee) as  the Committee shall determine and shall
    be evidenced by instruments in such form  as the Committee may from time  to
    time  approve. The Committee shall have the absolute discretion to determine
    whether any consideration (other  than the services  of the potential  award
    holder)  is  to be  received by  the  Corporation or  its subsidiaries  as a
    condition precedent to the issuance of shares pursuant to share rights.  The
    terms,  conditions and  restrictions to which  share rights  are subject may
    vary from grant to grant.
 
        (3)  SHARE UNITS.  A share unit granted under the Plan shall consist  of
    the right to receive an amount in cash equal to the Fair Market Value of one
    share  of Company Stock on the date  of valuation of the unit (together with
    cash dividend  equivalents if  so  determined by  the Committee)  less  such
    amount,  if any, as the  Committee shall specify. The  date of valuation and
    payment of cash under a share unit and the conditions, if any, to which such
    payment will be subject (whether  based on performance standards or  periods
    of  service or otherwise)  shall be determined by  the Committee. The terms,
    conditions and restrictions to which share  units are subject may vary  from
    grant to grant.
 
    (b)   WITHHOLDING.  The Committee may  require, or permit an award holder to
elect, that a portion of the total  value of the shares of Common Stock  subject
to  restricted shares or share rights held by  one or more award holders be paid
in the form of cash in lieu of the issuance of Company Stock and that such  cash
 
                                      A-7
<PAGE>
payment  be applied to the  satisfaction of the federal,  state and local income
and employment tax withholding obligations that arise at the time the restricted
shares and share rights become free of all restrictions under the Plan.
 
    (c)   CASH  PAYMENTS.   The  Committee may  provide  award holders  with  an
election to receive a percentage of the total value of the Company Stock subject
to  restricted shares or share rights in the  form of a cash payment, subject to
such terms, conditions and restrictions as the Committee shall specify.
 
    (d)  ELECTIVE AND TANDEM AWARDS.  The Committee may award restricted shares,
share rights and share units independently  of other compensation or in lieu  of
compensation  that would otherwise be paid in  cash or stock options, whether at
the election  of  the  potential  award  holder  or  otherwise.  The  number  of
restricted shares, share rights or share units to be awarded in lieu of any cash
compensation  amount  or number  of  stock options  shall  be determined  by the
Committee in  its  sole  discretion and  need  not  be equal  to  such  foregone
compensation  in Fair Market Value. In addition, restricted shares, share rights
and share units may be awarded in  tandem with stock options, so that a  portion
of such award becomes payable or becomes free of restrictions only if and to the
extent  that the tandem options  are not exercised or  are forfeited, subject to
such terms and conditions as the Committee may specify.
 
    (e)  MODIFICATION OF AWARDS.  Except to the extent an award is granted as  a
performance unit, the Committee may, in its sole discretion, modify or waive any
or  all of the  terms, conditions or restrictions  applicable to any outstanding
restricted share, share  right or share  unit; provided, however,  that no  such
modification  or  waiver  shall,  without  the  consent  of  the  holder  of  an
outstanding award, adversely affect the holder's rights thereunder.
 
    (f)  PERFORMANCE UNITS.   Effective March 8,  1996, the Committee may  grant
restricted shares, share rights and share units to 162(m) executives that comply
with  the requirements  of Code  Section 162(m).  Performance units  will become
payable or vest upon attainment of specified performance goals over a  specified
performance period.
 
        (1)   PERFORMANCE GOALS.   The Committee  will determine the Corporation
    performance goal or  goals that must  be met to  achieve the maximum  payout
    within  the shorter of the first 90 days of the specified performance period
    over which the performance goal  or goals will be  measured, or 25% of  such
    performance  period. The Committee  may establish a goal  based on more than
    one performance criteria, or  may establish multiple  goals, but any  payout
    must  be based on the  satisfaction of at least  one goal. The Committee may
    provide for different levels of payouts based on relative performance toward
    a performance goal.
 
        (2)  PERFORMANCE  CRITERIA.  Performance  units may be  based on one  or
    more  of the following  performance criteria: total  shareholder return; the
    achievement of a specified closing or average closing price of Common Stock;
    the absolute or percentage increase in the closing or average closing  price
    of  Common  Stock  and/or one  or  more  of the  following  measures  of the
    Corporation's net income for the specified performance period determined  in
    accordance  with  generally accepted  accounting principles  as consistently
    applied by the Corporation: absolute net income or a percentage or  absolute
    dollar  increase  in  net income,  earnings  per  share or  a  percentage or
    absolute dollar increase in earnings per share, or return on assets employed
    or equity, or a percentage or  absolute dollar increase in return on  assets
    employed  or  equity;  or the  Corporation's  absolute gross  revenues  or a
    percentage or absolute dollar increase  in gross revenues for the  specified
    performance   period  determined  in   accordance  with  generally  accepted
    accounting principles as consistently applied by the Corporation. The awards
    may be based on  the Corporation's performance  alone, or the  Corporation's
    performance  may be measured against  variously weighted published benchmark
    indices  that   the  Committee   determines   are  representative   of   the
    Corporation's  peer group, which  indices may include  the Standard & Poor's
    Health Care Composite Index, the  Standard & Poor's Health Care  Diversified
    Index and the AMEX Biotechnology Index, among others.
 
    For purposes of this Plan, net income and gross revenues shall be net income
    and  gross revenues of the Corporation  and its consolidated subsidiaries as
    reported by the Corporation and certified by its
 
                                      A-8
<PAGE>
    independent public accountants,  but the  Committee in fixing  any goal  may
    exclude any or all of the following if they have a material effect on annual
    net income or gross revenues: events or transactions that are either unusual
    in  nature or infrequent in occurrence (such as restructuring/reorganization
    charges, the  purchase  or  sale  of in  process  technology,  the  sale  or
    discontinuance  of a  business segment,  the sale  of investment securities,
    losses from  litigation,  the cumulative  effect  of changes  in  accounting
    principles, and natural disasters), depreciation, interest or taxes.
 
        (3)   REDUCTION OR CANCELLATION OF PERFORMANCE UNITS.  Final payouts are
    subject to the approval of the Committee, and the Committee has the absolute
    discretion to reduce or cancel any payout.
 
VII.  AUTOMATIC AWARDS TO DIRECTORS
 
    (a)  OPTIONS.   Effective March 8, 1996,  non-employee members of the  Board
("Eligible  Directors")  will  automatically  be  granted  nonstatutory  options
("Automatic  Options")  to  purchase  the  number  of  shares  of  Common  Stock
determined as set forth below (subject to adjustment under Section IV(c) hereof)
on the dates and terms set forth below:
 
        (1)   OPTION GRANTS.  On the last  business day of the second quarter of
    each  fiscal  year  of  the  Corporation  ("Automatic  Grant  Date"),   each
    continuing  Eligible Director (including each Eligible Director who is newly
    elected or appointed on the Automatic Grant Date) will receive an  Automatic
    Option to purchase that number of whole shares of Common Stock determined by
    dividing $100,000 by the Average Stock Price on the Automatic Grant Date.
 
        (2)    PRO RATA  OPTION GRANTS.   Each  person who  is newly  elected or
    appointed as an Eligible  Director on a date  other than an Automatic  Grant
    Date,  will  receive,  on  the  date of  such  election  or  appointment, an
    Automatic Option to  purchase a pro  rata number of  whole shares of  Common
    Stock  determined by multiplying  $8,333.33 by the  number of whole calendar
    months between the date of  the Eligible Director's election or  appointment
    and  the next Automatic Grant Date, and  dividing that number by the Average
    Stock Price on the grant date.
 
        (3)   ADVISORY COUNSELLORS.    Advisory Counsellors  of Cetus  will  not
    qualify for Automatic Options.
 
        (4)   TERMS AND CONDITIONS.  The terms and conditions applicable to each
    Automatic Option will be as follows:
 
            (i)  PRICE.  The option price per share will be equal to one hundred
       percent (100%) of the Fair Market Value  of one share of Common Stock  on
       the date of grant.
 
            (ii)   TERM.   Each Automatic  Option will  have a term  of ten (10)
       years, measured from the  date of grant, and  will be exercisable at  any
       time during the term for all or any part of the covered shares; provided,
       however,  that no Automatic Options may be exercised prior to approval of
       the Plan by the Corporation's stockholders.
 
           (iii)  REPURCHASE.  The shares purchased under the Automatic  Options
       will be subject to repurchase by the Corporation at the original exercise
       price  in  the  event  an  optionee ceases  to  provide  services  to the
       Corporation or its subsidiaries as a director, an employee, a  consultant
       or  an independent  contractor. The Corporation's  repurchase rights will
       lapse, and the optionee's interest in the purchased shares will vest,  in
       a  series of equal annual installments over the five-year period measured
       from the  grant date,  provided the  optionee continues  to provide  such
       services.  In addition, the Corporation's  repurchase right will lapse in
       its entirety, and the Automatic  Options will become fully vested  should
       one or more of the following events occur while the optionee is providing
       such  services: (A) the optionee's death, or (B) the optionee's permanent
       disability.
 
            (iv)  PAYMENT.   Upon exercise of the  Automatic Option, the  option
       price for the purchased shares will become payable immediately in cash or
       in shares of Common Stock that the optionee has held for at least six (6)
       months.  Payment  may also  be made  by delivery  of a  properly executed
       exercise notice together  with irrevocable  instructions to  a broker  to
       promptly  deliver to the  Corporation the amount of  sale proceeds to pay
       the option price.
 
                                      A-9
<PAGE>
            (v)   CESSATION.   In  the  event  the optionee  ceases  to  provide
       services  to  the  Corporation  or its  subsidiaries  as  a  director, an
       employee, a consultant or an independent contractor, the Automatic Option
       may be exercised, within the term  of the Automatic Option, for a  period
       of  three (3) months after the date of such cessation (twelve (12) months
       in the case of cessation by reason  of disability or death). In the  case
       of death, the Automatic Option may be exercised within such period by the
       estate or heirs of the optionee.
 
    (b)    SHARE  RIGHTS.   Effective  March  8, 1996,  Eligible  Directors will
automatically be granted share rights ("Automatic Share Rights") to receive  the
number  of shares  of Common  Stock determined  as set  forth below  (subject to
adjustment under Section IV(c) hereof) on the dates and terms set forth below:
 
        (1)  NEW DIRECTORS.  Each  newly elected or appointed Eligible  Director
    will  be granted, on the date of  such election or appointment, an Automatic
    Share Right to purchase that number  of whole shares determined by  dividing
    $40,000 by the Average Stock Price on the grant date.
 
        (2)  CONTINUING DIRECTORS.
 
            (i)   FULL GRANTS.     Subject to Subsection VII(b)(2)(ii) below, on
       each Automatic Grant  Date each incumbent,  continuing Eligible  Director
       will  be granted an Automatic Share Right to receive that number of whole
       shares of  Common Stock  determined by  dividing $25,000  by the  Average
       Stock  Price on the Automatic  Grant Date. Notwithstanding the foregoing,
       on the  Automatic Grant  Date  occurring in  June 1996,  each  continuing
       Eligible  Director elected  or appointed  before March  8, 1996,  will be
       granted an Automatic Share Right to  receive that number of whole  shares
       determined by using the $40,000 in lieu of the $25,000 figure.
 
           (ii)  PRO RATA GRANTS.    If an Eligible Director is newly elected or
       appointed  on  a  date  other  than  an  Automatic  Grant  Date,  on  the
       immediately succeeding Automatic Grant Date, such Eligible Director  will
       be  granted a  pro rata  Automatic Share Right  to receive  the number of
       whole shares  of Common  Stock determined  by multiplying  the number  of
       whole   calendar  months  since  the   Eligible  Director's  election  or
       appointment by $2,083.33 and  dividing the product  by the Average  Stock
       Price on the Automatic Grant Date.
 
        (3)    ADVISORY COUNSELLORS.   Advisory  Counsellors  of Cetus  will not
    qualify for Automatic Share Rights.
 
        (4)  TERMS AND CONDITIONS.  The terms and conditions applicable to  each
    Automatic Share Right will be as follows:
 
            (i)   TERM.  Each Automatic Share Right will have a term of five (5)
       years, measured from the grant date.
 
            (ii)  VESTING.  The Automatic Share  Right will vest in a series  of
       equal  annual installments  over the  five-year period  measured from the
       grant date, provided the Eligible Director continues to provide  services
       to  the Corporation  or its  subsidiaries as  a director,  an employee, a
       consultant or an independent contractor.  Shares of Common Stock will  be
       issued  in satisfaction  of the  Automatic Share  Right as  the Automatic
       Share Right vests.  In addition, full  vesting will occur  should one  or
       more  of  the  following  events occur  while  the  Eligible  Director is
       providing such services: (A)  the Eligible Director's  death, or (B)  the
       Eligible Director's permanent disability.
 
           (iii)    CESSATION.   In the  event the  Eligible Director  ceases to
       provide services to the Corporation or its subsidiaries as a director, an
       employee, a consultant or an independent contractor, the Automatic  Share
       Right shall terminate with respect to the unvested portion of the Award.
 
    (c)   COST-OF-LIVING INCREASES.  Each dollar  value used in this Article VII
will be subject to annual cost-of-living increases. The increases will be  based
on  the Consumer  Price Index, and  will occur automatically  beginning with the
1997 Automatic Grant Date.
 
                                      A-10
<PAGE>
    (d)  AVERAGE  STOCK PRICE.   Average Stock Price  means the average  closing
price  of one share  of Common Stock  as reported on  the Nasdaq National Market
System for the previous twelve month period ending on the last day of the  month
before the grant date of the award.
 
VIII.  LOANS AND INSTALLMENT PAYMENTS
 
    In  order to assist an award holder (including an employee who is an officer
or director of the  Corporation) in the acquisition  of shares of Company  Stock
pursuant  to  an  award granted  under  the  Plan (other  than  pursuant  to the
Automatic Award provisions of this Plan), the Committee may authorize, at either
the time of  the grant of  an award or  the time of  the acquisition of  Company
Stock  pursuant to the award (i) the extension  of a loan to the award holder by
the Corporation, (ii) the payment by the award holder of the purchase price,  if
any,  of  the Company  Stock  in installments,  or  (iii) the  guarantee  by the
Corporation of a loan obtained by the award holder from a third party. The terms
of any loans, guarantees  or installment payments,  including the interest  rate
and  terms of  repayment, will  be subject to  the discretion  of the Committee.
Loans, installment payments and guarantees may be granted without security,  the
maximum  credit available being the purchase price, if any, of the Company Stock
acquired plus the maximum federal and state income and employment tax  liability
that may be incurred in connection with the acquisition.
 
IX.  ASSIGNABILITY
 
    No  award granted under the Plan is  assignable or transferable by the award
holder other than by Will or by the laws of descent and distribution, and during
the lifetime of the award holder, only the award holder may exercise options  or
exercise the rights provided under awards granted under the Plan.
 
X.  CANCELLATION AND NEW GRANT OF OPTIONS
 
    The  Committee will have the authority to  effect, at any time and from time
to time, with the  consent of the affected  option holders, the cancellation  of
any  or all outstanding options  under the Plan, a Cetus  Prior Plan or a Chiron
Prior Plan (other than options  granted under automatic option grant  provisions
of these plans) and to grant in substitution therefor new options under the Plan
covering the same or different numbers of shares, but having an option price per
share  not less than eighty-five  percent (85%) of the  Fair Market Value on the
new grant date  or, in  the case  of an  Incentive Option,  one hundred  percent
(100%)  of the Fair Market  Value on the new  grant date (or, in  the case of an
Incentive Option granted to a 10% Stockholder, one hundred ten percent (110%) of
such Fair Market Value). If one or more of the cancelled options is an Incentive
Option granted before 1987 under a Cetus Prior Plan or a Chiron Prior Plan, then
such option  will,  solely  for  purposes  of  the  "sequential  exercise"  rule
applicable  to outstanding Incentive Options  granted before 1987, be considered
to be outstanding until the expiration  date initially specified for the  option
term of such option.
 
XI.  ACCELERATION AND TERMINATION OF AWARDS
 
    (a)   ACCELERATION.   In  the event  of an  agreement to  dispose of  all or
substantially all of the assets or outstanding capital stock of the  Corporation
by  means of a sale, merger, reorganization,  or liquidation, each award will be
automatically accelerated  so that  (1) options  become fully  exercisable  with
respect  to the total number of  shares purchasable under the options; provided,
however, that the  exercise of  accelerated Incentive Options  granted prior  to
1987  will remain  subject to  any limitations  imposed by  the Internal Revenue
Code's sequential exercise rule, (2)  restrictions on restricted shares will  be
eliminated, and the shares will immediately vest, and (3) share rights and share
units  will immediately vest and become  payable. The Committee may also provide
for the automatic termination of repurchase  rights upon the occurrence of  such
an event.
 
    (b)   NO ACCELERATION.  No acceleration of awards will occur if the terms of
the agreement require as  a prerequisite to the  consummation of any such  sale,
merger,  reorganization  or  liquidation that  each  such award  will  be either
assumed by the  successor corporation or  parent thereof or  be replaced with  a
comparable  award  subject  to shares  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.
 
                                      A-11
<PAGE>
Upon  consummation   of  the   sale,  merger,   reorganization  or   liquidation
contemplated  by the  agreement, all  awards, whether  or not  accelerated, will
terminate unless  assumed  pursuant to  a  written agreement  by  the  successor
corporation or parent thereof.
 
    (c)   CORPORATE STRUCTURE.   The grant of awards under  this Plan will 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.
 
XII.  VALUATION
 
    With  regard to all Substitute Options, Fair Market Value will be determined
in accordance  with the  relevant option  plan documents  on the  date that  the
outstanding options were granted. With regard to awards granted under this Plan,
for  all valuation purposes under the Plan, the  Fair Market Value of a share of
Common Stock or Restricted  Common Stock (as  the case may  be) on any  relevant
date will be determined in accordance with the following provisions:
 
    (a) If the Common Stock or Restricted Common Stock is not at the time listed
or   admitted  to  trading  on  any  stock   exchange,  but  is  traded  in  the
over-the-counter market, the Fair Market Value  will be the average between  the
reported  high price and the reported low price  of one share of Common Stock or
Restricted Common Stock  (as the case  may be) on  the date in  question 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 or Restricted 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 of one
share of Common Stock  or Restricted Common  Stock (as the case  may be) on  the
date in question 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 or Restricted Common  Stock (as the case may be) 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 (a) nor subparagraph  (b) above reflects Fair Market  Value
of  the stock  and the award  was not  granted pursuant to  the Plan's Automatic
Award provisions, then the Fair Market Value will be determined by the Committee
after taking into account such factors as the Committee deems appropriate, or in
the case of Automatic Awards, by an independent third party valuation.
 
XIII.  SURRENDER OF OPTIONS FOR CASH OR STOCK
 
    (a)  STOCK  APPRECIATION RIGHTS.   If,  and only  if the  Committee, in  its
discretion,  elects to implement an option surrender program under the Plan, one
or more option holders may, upon such terms and conditions as the Committee  may
establish  at the time of the option grant or at any time thereafter, be granted
the right to surrender all  or part of an unexercised  option in exchange for  a
distribution equal in amount to the difference between (i) the Fair Market Value
(at date of surrender) of the shares for which the surrendered option or portion
thereof  is at the time exercisable and  (ii) the aggregate option price payable
for such shares.  The distribution to  which an option  holder becomes  entitled
under  this Section may be  made in shares of  Common Stock or Restricted Common
Stock, valued at Fair Market Value at the date of surrender, in cash, or  partly
in  shares and partly in  cash, as the Committee,  in its sole discretion, deems
appropriate. The option surrender provisions of  this Section will not apply  to
options granted pursuant to the Automatic Option Grant provisions of this Plan.
 
    (b)  LIMITED STOCK APPRECIATION RIGHTS.  If outstanding options of Cetus for
which  Substitute Options  are issued  pursuant to  Section III(d)  have Limited
Stock Appreciation Rights ("LSARs") attached thereto, then each such LSAR  shall
be  honored  by  the  Corporation  in  accordance  with  its  terms  and  remain
exercisable for a  period of  60 days following  the date  that stockholders  of
Cetus  approve the  Merger; provided, however,  that if the  LSAR was originally
granted within 6 months of the date that Cetus stockholders approve the  Merger,
then  the LSAR will be exercisable for  a period of 60 days following expiration
of such six-month period. Upon expiration of the applicable 60-day period,  each
such LSAR not
 
                                      A-12
<PAGE>
previously  exercised shall expire. Upon exercise of an LSAR, the related option
will be cancelled, and Chiron will pay to the LSAR holder an amount in cash  for
each  share with respect to which the LSAR is exercised determined in accordance
with the terms of the Cetus Prior Plans.
 
XIV.  REPURCHASE RIGHTS
 
    The Committee may, in  its discretion, establish  as a term  of one or  more
awards  granted under the Plan  that the Corporation (or  its assigns) will have
the right, exercisable upon the  award holder's termination of employment  with,
or  cessation  of  services  for,  the  Corporation  and  its  subsidiaries,  to
repurchase at the original price  paid, if any, for  such shares of (1)  Company
Stock  acquired by the award holder pursuant to the granted award, or (2) Common
Stock into which acquired Restricted Common Stock may have been converted or for
which Restricted Common Stock may have been exchanged. Any such repurchase right
will be exercisable  by the  Corporation (or its  assigns) upon  such terms  and
conditions (including provisions for the expiration of such right in one or more
installments)  as the  Committee may specify  in the  instrument evidencing such
right. The Committee will also have full power and authority to provide for  the
automatic  termination of  the Corporation's repurchase  rights, in  whole or in
part, thereby accelerating  the vesting of  any or all  of the purchased  shares
(other than purchased shares obtained pursuant to the Automatic Award provisions
of  this Plan) upon the occurrence of any change in control specified in Article
XI.
 
XV.  RIGHT OF FIRST REFUSAL
 
    The Committee may, in  its discretion, establish  as a term  of one or  more
awards  granted under the Plan that the Corporation has a right of first refusal
with respect to the proposed disposition  by the award holder (or any  successor
in interest by reason of purchase, gift or other mode of transfer) of any shares
of (1) Company Stock acquired by the award holder pursuant to the granted award,
or  (2) Common Stock into which purchased  Restricted Common Stock may have been
converted or for which acquired Restricted Common Stock may have been exchanged.
Any such right of first  refusal will be exercisable  by the Corporation or  its
assigns  in accordance with the terms and conditions specified in the instrument
evidencing such right.
 
XVI.  EFFECTIVE DATE AND TERM OF PLAN
 
    (a)  EFFECTIVE DATE.   The Plan became effective  on December 10, 1991,  the
date  it was approved by the Corporation's  stockholders. The Plan as amended is
effective March 8, 1996, subject to approval by the Corporation's  stockholders.
Any  awards granted under  the amended provisions  of the Plan  adopted March 8,
1996 will be granted subject to  approval by the Corporation's stockholders.  If
such  stockholder approval of the  amendments is not obtained  by March 7, 1997,
then the Plan will continue in accordance with the Plan provisions in effect  on
March 7, 1996.
 
    (b)   TERM.  Incentive Options may be granted under the Plan only within ten
years of  the  Effective Date  of  the Plan.  Subject  to this  limitation,  the
Committee  may grant awards under the Plan  at any time after the Effective Date
of the Plan and before the Plan is terminated by the Board.
 
XVII.  AMENDMENT OR DISCONTINUANCE
 
    (a)  BOARD.  The Board may  amend, suspend or discontinue the Plan in  whole
or  in  part at  any  time; provided,  however, that  (a)  except to  the extent
necessary to qualify as Incentive Options  any or all options granted under  the
Plan  that are intended to so qualify,  such action may not, without the consent
of the award  holder, adversely affect  rights and obligations  with respect  to
awards outstanding under the Plan; (b) the provisions of the Plan concerning the
eligibility  of non-employee  members of  the Board  for awards  and the amount,
price and timing of Automatic Option Grants  under this Plan may not be  amended
more  than once  every six  months, other  than to  comport with  changes in the
Internal Revenue Code or  rules thereunder; and (c)  the Board may not,  without
the  approval  of the  Corporation's  stockholders (1)  materially  increase the
number of  shares of  Company Stock  subject to  awards under  the Plan  (unless
necessary   to  effect  the  adjustments  required  under  Section  IV(c)),  (2)
materially modify the eligibility requirements for awards under the Plan, or (3)
make  any  other  change  with  respect  to  which  the  Board  determines  that
stockholder approval is required by applicable law or regulatory standards.
 
                                      A-13
<PAGE>
    (b)   COMMITTEE.  The Committee will have full power and authority to modify
or waive any or all of the  terms, conditions or restrictions applicable to  any
outstanding  award  (other  than Automatic  Option  Grants), to  the  extent not
inconsistent with the Plan.
 
    (c)  SUBSTITUTE OPTIONS.  Substitute Options will be subject to amendment in
accordance with the terms of this Plan.
 
XVIII.  NO OBLIGATION
 
    Nothing contained in the Plan  (or in any award  granted under this Plan,  a
Chiron  Prior  Plan or  a  Cetus Prior  Plan)  shall confer  upon  any employee,
consultant, or independent contractor any right to continue in the employ of, or
to provide  services  to, the  Corporation  or  any affiliate  or  constitute  a
contract  or  agreement  of employment  or  for  the provision  of  services, or
interfere in any way with the right of the Corporation or an affiliate to reduce
such employee's, consultant's or independent contractor's compensation from  the
rate  in existence at the time of the  granting of an award or to terminate such
employee's, consultant's or independent  contractor's employment or services  at
any  time, with or  without cause; but nothing  contained in the  Plan or in any
award granted under this Plan shall affect any contractual rights of an employee
pursuant to a written employment agreement.
 
XIX.  USE OF PROCEEDS
 
    The cash proceeds  received by  the Corporation pursuant  to awards  granted
under the Plan will be used for general corporate purposes.
 
XX.  COMPLIANCE
 
    (a)    FEDERAL  AND  STATE  LAWS.   No  option  may  be  exercised,  and the
Corporation will not be obligated to issue stock under any award unless, in  the
opinion  of  counsel  for the  Corporation,  such  exercise and  issuance  is in
compliance with all applicable federal and state securities laws. As a condition
to the grant  of any award,  or to the  issuance of stock  under any award,  the
Committee may require that the award holder agree to comply with such provisions
of  federal and state securities laws as may  be applicable to such grant, or to
the sale of  stock acquired  pursuant to  the Plan,  and that  the award  holder
deliver   to  the  Corporation  a  written  agreement,  in  form  and  substance
satisfactory to the Corporation and its counsel, implementing such agreement.
 
    (b)   INFORMATION.   The  Corporation  will  furnish to  each  award  holder
participating  in the Plan (other  than a key employee or  a director) a copy of
the Corporation's Annual Report to Stockholders for the most recent fiscal year,
and additional copies will be furnished,  without charge, to such award  holders
upon request to the Secretary of the Corporation.
 
                                      A-14
<PAGE>
                                   APPENDIX A
           SPECIAL PROVISIONS RELATED TO 1995 CIBA-GEIGY TRANSACTION
 
    Those  persons holding options  to acquire shares of  Common Stock under the
Corporation's 1991  Stock Option  Plan  on November  20,  1994 are  granted  the
following rights ("Rights") with respect to each such option:
 
    (i)  the right to receive upon the  closing of the tender offer contemplated
under the Investment Agreement entered into  on such date among the  Corporation
and  Ciba-Geigy Limited,  Ciba-Geigy Corporation  and Ciba  Biotech Partnership,
Inc. (the "Closing") a cash payment equal to (A) 37.33% of the number of  shares
of  Common  Stock with  respect to  which  each such  option would  first become
exercisable in calendar year 1995 multiplied by (B) the difference between  $117
per  share and the exercise price per share  of such option with respect to such
shares and
 
    (ii) with respect to  the remaining shares of  Common Stock subject to  each
such  option, the right, exercisable at any  time after the later of the Closing
or the date that such an option  first becomes exercisable with respect to  such
shares,  to surrender  that portion  of such option  relating to  37.33% of such
shares in return for a cash payment equal to (A) the difference between $117 per
share and the  exercise price per  share of  such option multiplied  by (B)  the
number  of shares with respect to which  such option is so surrendered. However,
the grant and exercise of any such right with respect to any officer or director
subject to Section 16 of the Securities Exchange Act of 1934 shall be subject to
stockholder approval  of the  grant of  such rights  at the  Corporation's  1995
stockholder  meeting. The grant of  such rights, which are  made with respect to
1,858,776 optioned shares shall be in addition to, and shall not count  against,
the  aggregate and annual limits  on the number of  shares with respect to which
other awards under  the Plan  may be  made to  all individuals  and/or a  single
individual.
 
                                      A-15
<PAGE>


                              CHIRON CORPORATION
            THIS PROXY IS SOLICITED ON BEHALF OF THE BOARD OF DIRECTORS


   The undersigned hereby appoints Dr. William J. Rutter and Dr. Edward E. 
Penhoet, and each of them, with full power of substitution, the proxies of 
the undersigned to vote all shares of Common Stock of Chiron Corporation (the 
"Company") which the undersigned is entitled to vote at the Annual Meeting of 
Stockholders of the Company to be held at 1450 53rd Street, Emeryville, 
California, on May 16, 1996 at 10:00 a.m., and at any adjournments or 
postponements thereof, with the same force and effect as the undersigned 
might or could do if personally present thereat:

                                                                I PLAN TO ATTEND
                                                                THE MEETING
                                                                      / /

1.  ELECTION OF DIRECTORS           / / FOR all nominees listed below
    (THE BOARD OF DIRECTORS             (except as marked to the contrary
    RECOMMENDS A VOTE FOR.)             below.)

    / / WITHHOLD AUTHORITY
        to vote for all nominees listed
        below.

INSTRUCTION: TO WITHHOLD AUTHORITY TO VOTE FOR ONE OR MORE INDIVIDUAL 
             NOMINEES, STRIKE A LINE THROUGH THE NOMINEE'S NAME IN THE LIST
             BELOW.

       Dr. William J. Rutter - Mr. Jack W. Schuler - Mr. Lewis W. Coleman

2.  Proposal to approve and adopt an amendment to the Company's Restated 
    Certificate of Incorporation to increase the authorized number of shares of 
    Common Stock of the Company from 100 million to 500 million, as set forth 
    in the Chiron Corporation Proxy Statement for the Annual Meeting of 
    Stockholders to be held May 16, 1996. (The Board of Directors recommends 
    a vote FOR.)

              / / FOR          / / AGAINST        / / ABSTAIN

3.  Proposal to approve amended Chiron 1991 Stock Option Plan to change the 
    formula for granting automatic annual stock options to non-employee 
    directors, to add an annual grant of automatic share rights for 
    non-employee directors and to add performance units, which are restricted 
    shares, share rights and share units awarded to corporate vice-presidents 
    and other executive officers which comply with the requirements of Internal
    Revenue Code Section 162(m), as set forth in the Chiron Corporation Proxy 
    Statement for the Annual Meeting of Stockholders to be held May 16, 1996. 
    (The Board of Directors recommends a vote FOR.)

              / / FOR          / / AGAINST        / / ABSTAIN

                         (Continued on reverse side)

<PAGE>


4.  Proposal to ratify the selection of KPMG Peat Marwick LLP as independent 
    public accountants for the Company for the fiscal year ending December 31, 
    1996. (The Board of Directors recommends a vote FOR.)

              / / FOR          / / AGAINST        / / ABSTAIN

5.  In their discretion, the Proxies are authorized to vote upon such other 
    business as may properly come before the meeting.

    THIS PROXY WHEN PROPERLY EXECUTED WILL BE VOTED IN THE MANNER DIRECTED 
HEREIN BY THE UNDERSIGNED STOCKHOLDER. IF NO DIRECTION IS MADE, THIS PROXY 
WILL BE VOTED FOR PROPOSALS 1, 2, 3 AND 4.


                                       Dated_______________________________1996
                                                 (Be Sure to Date Proxy)

                                       _________________________________________
                                                      (Signature)

                                       _________________________________________
                                                      (Signature)


                                       Please sign exactly as name appears at
                                       left. When shares are held by joint
                                       tenants, both should sign. When signing
                                       as attorney, executor, administrator,
                                       trustee, or guardian, please give full
                                       title as such. If a corporation, please
                                       sign in full corporate name by President
                                       or other authorized person. If a partner-
                                       ship, please sign in full partnership 
                                       name by authorized person.


         PLEASE MARK, SIGN, DATE AND RETURN THE PROXY CARD PROMPTLY,
                         USING THE ENCLOSED ENVELOPE




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