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                             REVOLVING CREDIT AGREEMENT

     REVOLVING CREDIT AGREEMENT (this "AGREEMENT") dated as of March 23, 1998
(the "EFFECTIVE DATE") between CHIRON CORPORATION, a Delaware corporation (the
"BORROWER"), and SWISS BANK CORPORATION, STAMFORD BRANCH (the "BANK").

     WHEREAS, subject to and upon the terms and conditions set forth herein, the
Bank is willing to make available to the Borrower the credit facility provided
for herein;

     NOW, THEREFORE, IT IS AGREED:

     1.   THE ADVANCES.  Subject to and upon the terms and conditions set forth
herein, the Bank agrees to make advances (the "ADVANCES") to the Borrower at any
time and from time to time prior to March 22, 1999 (the "EXPIRY DATE");
provided, however, that the aggregate principal amount of Advances outstanding
shall at no time exceed U.S. $100,000,000 (One Hundred Million U.S. Dollars)
(the "COMMITMENT").

     2.   PURPOSE.  The Borrower shall use the proceeds of the Advances for
general corporate purposes, including acquisition financing.  The Borrower
agrees to indemnify the Bank and hold the Bank harmless from and against any and
all liabilities, losses, damages, costs and expenses of any kind which may be
incurred by the Bank relating to or arising out of any actual or proposed use of
proceeds of Advances hereunder.

     3.   AVAILABILITY.  The following Advances shall be available to the
Borrower hereunder:  (a) Prime Rate Advances and Money Market Rate Advances of
up to 270 days; or (b) Eurodollar Rate Advances of one, two, three, six or nine
months.  For the purposes of this Agreement, it is understood that (i) the
duration of each Advance shall be referred to as an "INTEREST PERIOD"; (ii) the
Borrower is required to repay each Advance on the last day of the Interest
Period for such Advance; and (iii) no Advance shall have an Interest Period
which extends beyond the Expiry Date.

     4.   INTEREST.  Interest shall be payable in respect of the outstanding
principal amount of each Advance at the maturity thereof.  Advances shall bear
interest at the following rates per annum:  (a) if a Prime Rate Advance, at the
Bank's floating Prime Rate; (b) if a Money Market Rate Advance, at the quoted
Money Market Rate; or (c) if a Eurodollar Rate Advance, 0.14 of 1% in excess of
the Bank's Eurodollar Rate.


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          Overdue principal and, to the extent permitted by law, overdue
interest in respect of each Advance and any other overdue amount payable by the
Borrower hereunder shall bear interest, payable on demand, at a rate per annum
equal to 2-1/2% per annum in excess of the Bank's Prime Rate in effect from time
to time.

          For the purposes of this Agreement, "PRIME RATE" and "MONEY MARKET
RATE" shall mean those rates so designated by the Bank or determined in
accordance with the practice of the Bank from time to time, it being understood
that the Prime Rate shall in no event be less than 1/2 of 1% in excess of the
rate payable by the Bank from time to time for overnight Federal funds.  The
Bank shall determine the "EURODOLLAR RATE"  by taking the rate for a loan of a
comparable amount and duration as the proposed Advance from page 3750 of the
"Telerate Screen".

     5.   INCREASED COSTS. If at any time the Bank shall have determined (which
determination shall, absent manifest error, be final, conclusive and binding on
all parties hereto) that as a result of any change in any applicable law or
governmental rule, regulation or order (including any applicable law or
governmental rule, regulation or order respecting capital adequacy), or any
interpretation thereof, including the enactment of any law or governmental rule,
regulation or order (whether or not having the force of law), the cost to the
Bank of maintaining its Commitment hereunder or making, funding or maintaining
any Advance shall be increased or the yield to the Bank on such Advance shall be
diminished, then the Bank shall promptly notify the Borrower thereof, showing in
reasonable detail the basis for the calculation of such increased costs or
diminished yield, and the Borrower shall pay to the Bank an amount sufficient to
indemnify the Bank thereagainst.

     6.   COMMITMENT FEE.  The Borrower shall pay the Bank a fee ("COMMITMENT
FEE") computed at a rate per annum of 0.06 of 1% on the average daily unused
portion of the Commitment.  Accrued Commitment Fee shall be payable quarterly on
the last business day of each calendar quarter and on the Expiry Date or earlier
termination of the Commitment.

     7.   NOTICE OF INTENTION TO BORROW.  The Borrower shall give the Bank prior
notice at its address on the signature page hereof (a "NOTICE OF BORROWING") by
telephone or facsimile (to be subsequently confirmed in writing) or in writing
(effective upon receipt) of its intention to borrow, specifying the date,
amount, type and tenor of the proposed Advance.  The Borrower shall give such
Notice of Borrowing at least two business days prior to any proposed Eurodollar
Rate Advance and by 10:00 a.m. New York time on the date of any proposed Prime
Rate Advance.

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     8.   MONEY MARKET RATE ADVANCES.  The Borrower may request a Money Market
Rate quote by telephone on any business day.  If the Borrower accepts such Money
Market Rate, it must confirm such acceptance in writing.

     9.   PAYMENTS.  All payments made hereunder or under the Note (as
hereinafter defined) shall be made to the Bank without deductions for any
present or future taxes, withholdings, deductions or any other charges (the
"TAXES") imposed or required by any political or taxing authority, it being
understood that the net amount received by the Bank after payment of the Taxes
by the Borrower shall not be less than the payment provided for hereunder.  All
payments shall be made to the office of Swiss Bank Corporation in Stamford,
Connecticut, Account Number 101-WA-183008-000 Ref. Chiron Corporation.
Commitment Fee and interest payments (except with respect to Prime Rate
Advances) shall be calculated for the actual number of days elapsed on the basis
of a 360-day year.  Interest payments with respect to Prime Rate Advances shall
also be calculated for the actual number of days elapsed but on the basis of a
365- or 366-day year, as the case may be.

     10.  PREPAYMENT, FUNDING COSTS.  Any Prime Rate Advance may be prepaid
without premium or penalty upon two business days' prior notice to the Bank.  If
for any reason Eurodollar Rate or Money Market Rate Advances are prepaid, as a
result of acceleration or otherwise, or if the Borrower fails for any reason to
borrow in accordance with a Notice of Borrowing, the Borrower shall pay to the
Bank, on demand, an additional amount as shall be required to compensate the
Bank for any loss connected with its reemployment of the amount so prepaid or of
those funds acquired by the Bank to fund the Advance proposed in such Notice of
Borrowing, as the case may be.

     11.  CONDITIONS PRECEDENT.  The obligation of the Bank to make Advances to
the Borrower hereunder is subject to the satisfaction of the following
conditions on or before the Effective Date (except as hereinafter indicated):

          (a)  The Bank shall have received a duly executed note (the "NOTE") in
     the form of EXHIBIT A hereto.

          (b)  There shall have been delivered to the Bank (i) certified copies
     of (x) the Borrower's charter and by-laws and (y) resolutions of the
     Borrower's board of directors or equivalent body authorizing the
     transaction evidenced hereby, and (ii) evidence satisfactory to the Bank of
     the authority of the Borrower's signatory(ies) hereto and to the Note.

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          (c)  At the time of the making of each Advance, and after giving
     effect thereto, there shall exist no Event of Default (as hereinafter
     defined) and no condition, event or act which, with the giving of notice or
     lapse of time or both, would constitute an Event of Default, and all
     representations and warranties made by the Borrower herein shall be true
     and correct with the same effect as if those representations and warranties
     had been made on and as of such date.

          (d)  The Bank shall have received from Novartis AG (the "GUARANTOR")
     an unconditional guaranty in the amount of US$100,000,000 (One Hundred
     Million United States Dollars) of the Borrower's obligations hereunder and
     under the Note (the "GUARANTY").

     12.  REPRESENTATIONS AND WARRANTIES.  The Borrower makes the following
representations and warranties, all of which shall survive the execution and
delivery of this Agreement:

          (a)  The Borrower is duly organized and validly existing in good
     standing in the jurisdiction of its incorporation.

          (b)  This Agreement and the Note are duly and properly authorized and
     executed by the Borrower and will constitute its legal, valid and binding
     obligations enforceable in accordance with their respective terms.

     13.  COVENANTS.  The Borrower covenants and agrees that, until all
obligations incurred by the Borrower under this Agreement are paid in full and
so long as the Commitment is in effect, the Borrower will:

          (a)  Provide to the Bank (i) as soon as they are available, copies of
     all financial statements of the Borrower required to be filed with the
     Securities and Exchange Commission; and (ii) with reasonable promptness,
     any other information as the Bank may from time to time reasonably request.

          (b)  Promptly give written notice to the Bank of any condition, event
     or act which, with or without the giving of notice or the lapse of time, or
     both, would constitute an Event of Default (as hereinafter defined).

          (c)  Not wind up, liquidate or dissolve its affairs or merge or
     consolidate into any entity, or convey, sell, lease or otherwise dispose of
     (or agree to do any of the foregoing at any future time) all or
     substantially all or a

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     substantial part of its property or assets, except that (i) any
     corporation may merge or liquidate into the Borrower provided that either
     (x) the Borrower shall be the surviving corporation, or (y) if the
     Borrower is not the surviving corporation, the Guaranty shall remain in
     full force and effect on behalf of the surviving corporation, and (ii)
     the Borrower may merge into the Guarantor.

     14.  EVENTS OF DEFAULT.  If any of the following events ("EVENTS OF
DEFAULT") shall occur and be continuing:

          (a)  The Borrower shall default in the payment of any principal amount
     due hereunder or under the Note, or shall default in the payment of any
     interest amount due hereunder or under the Note and such default shall not
     be cured within five (5) days;

          (b)  The Borrower shall fail to perform or observe any material term
     or covenant contained in this Agreement and such failure shall not be
     remedied within 30 days, or any representation or warranty made by the
     Borrower in this Agreement or in any certificate or other document or
     statement furnished at any time hereunder or in connection herewith shall
     prove to have been incorrect or untrue in any material respect on the date
     as of which made;

          (c)  A default or event of default with respect to payment shall occur
     in respect of bonds, notes, other loans or similar evidences of
     indebtedness of the Borrower or any subsidiary in a principal amount of at
     least U.S.$ 5,000,000.00, the effect of which is to cause, or to permit the
     holder of such indebtedness to cause, such indebtedness to become due prior
     to its stated maturity, or any such indebtedness shall not be paid within
     any applicable grace period after the due date thereof;

          (d)  The Guaranty shall cease to be in full force and  effect for any
     reason whatsoever; or

          (e)  The Borrower or the Guarantor shall make an assignment for the
     benefit of creditors, shall generally fail to pay its debts as they become
     due, shall file a petition commencing a voluntary case under any
     reorganization or bankruptcy laws, or an involuntary case under such laws
     shall be commenced against the Borrower or the Guarantor and such
     proceeding shall remain undismissed or unstayed for a period of 30 days;

then, and in any such event, the Bank may by notice to the Borrower take either
or both of the following actions:  (i)

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terminate the Commitment, whereupon the same shall terminate forthwith,
and/or (ii) declare the Advances and all interest accrued and unpaid thereon,
any accrued Commitment Fee, and all other sums due hereunder, to be
immediately due and payable without presentment, demand, protest or further
notice of any kind, all of which are hereby expressly waived by the Borrower.

     15.  GOVERNING LAW AND JURISDICTION; WAIVER OF JURY TRIAL.  THIS AGREEMENT
SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF
NEW YORK.

     THE PARTIES HERETO HEREBY IRREVOCABLY AND UNCONDTIONALLY WAIVE TRIAL BY
JURY.

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     IN WITNESS WHEREOF, the Borrower and the Bank have caused their duly
authorized officers to execute and deliver this Agreement as of the date first
above written.


                                           CHIRON CORPORATION


                                           By: /S/JE KENT
                                              ------------------------------
                                              Title: James E. Kent
                                              Vice President and Treasurer

                                              ADDRESS FOR NOTICES
                                              4460 Horton Street
                                              Emeryville, CA  94608
                                              Attention:  Treasurer
                                              Phone:  510-655-8730
                                              Fax:  510-601-3343


                                              SWISS BANK CORPORATION,
                                              STAMFORD BRANCH


                                            By /s/ JORG RAUTHE
                                              ------------------------------
                                              Title: Associate Director
                                                     Loan Portfolio Support, US


                                            By /s/ DOROTHY MCKINLEY
                                              ------------------------------
                                              Title: Associate Director
                                                     Loan Portfolio Support, US


                                              ADDRESS FOR NOTICES
                                              Swiss Bank Corporation
                                              677 Washington Boulevard
                                              P.O. Box 120300
                                              Stamford, Connecticut  06912
                                              Attention:  Lynn Alfaro
                                              Phone:  (203) 719-4308
                                              Fax:  (203) 719-3180

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                                   PROMISSORY NOTE


U.S. $100,000,000                                            March 23, 1998


     FOR VALUE RECEIVED, the undersigned, CHIRON CORPORATION, a Delaware
corporation the "BORROWER"), hereby promises to pay to the order of SWISS BANK
CORPORATION (the "BANK"), acting through its Stamford Branch, in lawful money of
the United States of America, in immediately available funds, at the principal
office of the Bank at 677 Washington Boulevard, Stamford, Connecticut  06912,
the principal amount of each advance (an "ADVANCE") endorsed on the schedule
attached hereto (the "SCHEDULE") on the maturity date thereof.

     The Borrower promises also to pay interest on the unpaid principal amount
of each Advance in like money from and including the date of each Advance until
paid in full at the rate specified in the Schedule, such interest to be paid on
the last day of the Interest Period for such Advance.  Interest shall be
calculated for the actual number of days elapsed (i) on the basis of a 365- or
366-day year, as the case may be, in the case of any Advance bearing interest at
a rate based on the Bank's Prime Rate, or (ii) on the basis of a 360-day year,
for all other Advances.

     The Borrower hereby authorizes the Bank to endorse on the Schedule the
date, amount and maturity date of, and interest rate with respect to, each
Advance evidenced thereby and all payments of principal thereof, provided that
the failure to make or any error in making such endorsement shall not affect the
obligations of the Borrower to the Bank.

     This note is the Note referred to in the Revolving Credit Agreement dated
as of March 23, 1998 between the Borrower and the Bank (as from time to time in
effect, the "AGREEMENT") and is entitled to the benefits thereof.

     If an Event of Default (as defined in the Agreement) shall occur and be
continuing, the principal of and accrued interest on this note may be declared
to be due and payable in the manner and with the effect provided in the
Agreement.

     The Borrower hereby waives presentment, demand, protest or notice of any
kind in connection with this note.


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     THIS NOTE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF
THE STATE OF NEW YORK.


                              CHIRON CORPORATION


                              By:  /S/ JE KENT
                                 --------------------------------
                              Title: Vice President and Treasurer