<PAGE>

                                 PROMISSORY NOTE

                             as Amended and Restated


$50,760,000                                                   New York, New York
                                                                 January 1, 1995


          FOR VALUE RECEIVED, the undersigned, CIBA CORNING DIAGNOSTICS CORP., a
Delaware corporation ("DIAGNOSTICS"), hereby promises to pay to the order of
CIBA-GEIGY LIMITED, a Swiss Corporation ("CIBA"), an amount equal to Fifty
million seven hundred sixty thousand Dollars ($50,760,000).  The entire
principal amount outstanding on this Note shall be repaid on January 1, 2000 (or
if such date is not a Business Day on the next succeeding Business Day).
Interest shall be payable on the same date as the principal amount, as provided
above, at an interest rate determined in accordance with the next paragraph of
this Note on the outstanding balance of the Note (computed on the basis of the
actual number of days principal is outstanding from and including the date
hereof, to but excluding the date of repayment, in a year of 365 days) and
compounded on a semi-annual basis.  All payments shall be made in lawful money
of the United States of America in immediately available funds to Ciba at Swiss
Bank Corporation, New York, NY, Account Number 0-452-702625-00 or such other
account as Ciba may designate in writing.  Payments received for value after
3:00 p.m., New York City time, shall be treated as being received on the next
succeeding Business Day.

          During the period that (i) there are loans outstanding under the
credit facility (the "CREDIT FACILITY") referred to in Section 5.12 of the
Investment Agreement dated as of November 20, 1994, among Ciba, Ciba-Geigy
Corporation, a New York corporation, CIBA Biotech Partnership Inc., a Delaware
corporation, and Chiron Corporation, a Delaware corporation ("CHIRON"), the
interest rate per annum on the outstanding balance of this Note shall be the
weighted average interest rate per annum for all outstanding loans to Chiron
under the Credit Facility and the interest rate hereunder shall be adjusted from
time to time simultaneously with any adjustment of such interest rate under the
Credit Facility and (ii) there are no loans outstanding under the Credit
Facility, the interest rate per annum on the outstanding balance of this Note
shall be a floating rate at all times during each calendar quarter during such
period equal to LIBOR plus 0.20%.  During such

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                                                                               2

times that the interest rate is determined in accordance with clause (i) of the
preceding sentence, Diagnostics shall notify Ciba in writing within 30 Business
Days of the end of each calendar quarter (or, with respect to the last calendar
quarter prior to the maturity of this Note, by the end of such calendar quarter)
of the information necessary to determine such interest rate and, promptly
thereafter, Ciba shall advise Diagnostics in writing of its determination of
such interest rate, and Ciba's determination thereof shall be final absent
manifest error.  During such times that the interest rate is determined in
accordance with clause (ii) of the preceding sentence, Ciba, on the first
business Day of each calendar quarter, shall advise Diagnostics in writing of
its determination of such interest rate (including any resetting thereof in
accordance with the definition of LIBOR), and Ciba's determination thereof shall
be final absent manifest error.

          Time shall be of the essence with regard to the repayment to Ciba of
all sums due and payable under this Note.

          Diagnostics promises to pay interest, on demand, on any overdue
principal and, to the extent permitted by law, overdue interest from their due
date at the rate of 10% per annum, compounded quarterly (the "DEFAULT RATE").
Diagnostics also agrees to pay on demand all costs and expenses of collecting
and enforcing this Note incurred by Ciba or any assignee.  Such costs and
expenses include, without limitation, reasonable costs of counsel.  Interest
shall accrue on unpaid costs and expenses from the date of demand to the date
of payment at the Default Rate.

          Anything herein to the contrary notwithstanding, if during any period
for which interest in computed hereunder, the amount of interest computed on the
basis provided for in this Note, together with all fees, charges and other
payments which are treated as interest under applicable law, as provided for
herein or in any other document executed in connection herewith, would exceed
the amount of such interest computed on the basis of the Highest Lawful Rate (as
defined below), Diagnostics shall not be obligated to pay, and Ciba shall not be
entitled to charge, collect, receive, reserve or take, interest in excess of the
Highest Lawful Rate, and during any such period the interest payable hereunder
shall be computed on the basis of the Highest Lawful Rate.  As used herein,
"HIGHEST LAWFUL RATE" means the maximum non-usurious rate of interest, as in
effect from time to time, which may be charged, contracted

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                                                                               3

for, reserved, received or collected by Ciba in connection with this Note under
applicable law.

          Capitalized terms appearing in this Note if not defined in the
operative paragraph hereof are defined in the DEFINITIONS section appearing at
the end of this Note.

          Diagnostics has the right at any time and from time to time to prepay
principal and any accrued unpaid interest thereon, in whole or in part, upon at
least five day's prior written or telecopy notice (or telephone notice promptly
confirmed by written or telecopy notice) to Ciba with a copy to Swiss Bank
Corporation.  Any such prepayments shall be applied, first, against any accrued
unpaid interest then outstanding under the Note and, second, against the
principal amount then outstanding under the Note as of the date of such
prepayment.  Prepayment of any amount of the principal of or interest on this
Note shall in no way extend the date of maturity.  Such amounts prepaid may not
be reborrowed.

          Diagnostics hereby waives diligence, presentment, demand, protest and
notice of any kind whatsoever.  The nonexercise by the holder or assignee of any
of its rights hereunder in any particular instance shall not constitute a waiver
thereof in that or any subsequent instance.

          The payment and any prepayments of the principal hereof and interest
hereon and the respective dates thereof shall be endorsed by the holder hereof
on the schedule attached hereto and made a part hereof or on a continuation
thereof which shall be attached hereto and made a part hereof, or otherwise
recorded by such holder in its internal records; PROVIDED, HOWEVER, that the
failure of the holder hereof to make such a notation or any error in such
notation shall not affect the obligations or Diagnostics under this Note.

COVENANTS

          Diagnostics covenants and agrees with Ciba that, so long as any
principal or interest under this Note (or cost or expense of collecting or
enforcing this Note) shall be unpaid, unless (i) Chiron agrees to guarantee the
principal and interest payable under this Note pursuant to an agreement
satisfactory in form and substance to Ciba or (ii) Ciba shall otherwise consent
in writing, Diagnostics

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will not, and will not cause or permit any of its subsidiaries to:

          (a) Create, incur, assume or permit to exist any Lien on any property
     or assets (including stock or other securities of any person, including any
     subsidiary) now owned or hereafter acquired by it or on any income or
     revenues or rights in respect of any thereof, (x) except to the extent the
     obligations of Diagnostics under this Note are equally and ratably secured
     by such property or assets pursuant to documentation in form and substance
     reasonably satisfactory to Ciba and (y) except:

                 (i) Liens on property or assets of Diagnostics and its
          subsidiaries existing on the date hereof; PROVIDED that such Liens
          shall secure only those obligations which they secure on the date
          hereof;

                (ii) any Lien existing on any property or asset prior to the
          acquisition thereof by Diagnostics or any subsidiary; PROVIDED that
          (x) such Lien is not created in contemplation of or in connection with
          such acquisition and (y) such Lien does not apply to any other
          property or assets of Diagnostics or any subsidiary;

               (iii) Liens for taxes not yet due or which are being contested;

                (iv) carriers', warehousemen's, mechanic's, materialmen's,
          repairmen's or other like Liens arising in the ordinary course of
          business and securing obligations that are not due or which are being
          contested;

                 (v) pledges and deposits made in the ordinary course of
          business in compliance with workmen's compensation, unemployment
          insurance and other social security laws or regulations;

                (vi) deposits to secure the performance of bids, trade contracts
          (other than for Indebtedness), leases (other than capital lease
          obligations), statutory obligations, surety and appeal bonds,
          performance bonds and other obligations of a like nature incurred in
          the ordinary course of business;

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               (vii) zoning restrictions, easements, rights-of-way, restrictions
          on use of real property and other similar encumbrances incurred in the
          ordinary course of business which, in the aggregate, are not
          substantial in amount and do not materially detract from the value of
          the property subject thereto or interfere with the ordinary conduct of
          the business of Diagnostics or any of its subsidiaries;

              (viii) purchase money security interests in real property,
          improvements thereto or tangible personal property hereafter acquired
          (or, in the case of improvements, constructed) by Diagnostics or any
          subsidiary; PROVIDED that (A) such security interests are incurred,
          and the Indebtedness secured thereby is created, within 90 days after
          such acquisition (or construction), (B) the Indebtedness secured
          thereby does not exceed 100% of the lesser of the cost or the fair
          market value of such real property, improvements or equipment at the
          time of such acquisition (or construction) and (C) such security
          interests do not apply to any other property or assets of Diagnostics
          or any of its subsidiaries;

                (ix) Liens on any property or assets of Diagnostics' foreign
          subsidiaries; PROVIDED, that Diagnostics and its U.S. subsidiaries
          shall not transfer property or assets to Diagnostics' foreign
          subsidiaries for the purpose of avoiding the prohibition of this
          paragraph (a);

                 (x) judgment Liens, if, within 60 days after the entry thereof,
          the judgment secured thereby shall have been discharged, vacated,
          reversed or execution thereof shall have been stayed pending appeal,
          or shall have been discharged, vacated or reversed within 60 days
          after expiration of any such stay;

                (xi) Liens to secure indebtedness from time to time outstanding;
          PROVIDED, that any such indebtedness secured by Liens which are not
          otherwise permitted by clauses (i) through (x) above or clause (xii)
          below does not exceed $25 million in the aggregate; and

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               (xii) extensions, renewals and replacements of Liens permitted
          under clauses (i) through (xi) above, PROVIDED, that any such
          extension, renewal or replacement Lien shall be limited to the
          property encumbered by the Lien extended, renewed or replaced and 
          the principal amount of indebtedness secured by any such extension, 
          renewal or replaacement Lien shall not exceed the principal amount 
          of the indebtedness secured by the Lien extended, renewed or replaced
          which is outstanding at the time of such extension, renewal or
          replacement.

          (b)  Cause, through any action or otherwise (including the declaration
     or making of any dividend or distribution with respect to its capital stock
     or through the transfer or disposition of any assets), other than through
     the operation of their businesses in the ordinary course, the consolidated
     shareholders' equity of Diagnostics and its consolidated subsidiaries at
     any time to be less than the greater of (A) $84 million and (B) the sum of
     X minus Y minus Z, where X equals $135 million, Y equals the amount of any
     purchase accounting adjustments to Diagnostics' consolidated shareholders'
     equity arising out of the transactions contemplated by the Investment
     Agreement, and Z equals the amount of any reductions in Diagnostics'
     consolidated shareholders' equity arising out of any agreement with Ciba by
     Chiron to assume sponsorship of or any liability under any defined benefit
     pension plan or any supplemental retirement plan covering employees of
     Diagnostics or its subsidiaries (all as determined in accordance with U.S.
     generally accepted accounting principles consistently applied).

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EVENTS OF DEFAULT

          In case of the happening of any of the following events ("EVENTS OF
     DEFAULT"):

          (a) Chiron or Diagnostics shall assert, or a court of competent
     jurisdiction shall determine pursuant to a final, nonappealable judgment,
     that this Note (subject to applicable bankruptcy, insolvency, fraudulent
     transfer, reorganization, moratorium and other laws affecting creditors'
     rights generally) shall not be enforceable in accordance with its terms;

          (b) a failure to perform or observe any term, covenant or agreement
     contained above under the caption "COVENANTS" in this Note, which failure
     is not cured within 30 days of such failure;

          (c) a failure to perform or observe any term, covenant or agreement
     contained in this Note (other than those referred to in the preceding
     clause (b)), which failure is not cured within 30 days of receipt by
     Diagnostics of notice of such default;

          (d) an involuntary proceeding shall be commenced or an involuntary
     petition shall be filed in a court of competent jurisdiction seeking (i)
     relief in respect of Chiron, Diagnostics or any of their Significant U.S.
     Subsidiaries, or of a substantial part of the property or assets of Chiron,
     Diagnostics or any of their Significant U.S. Subsidiaries, under Title 11
     of the United States Code, as now constituted or hereafter amended, or any
     other Federal or state bankruptcy, insolvency, receivership or similar law,
     (ii) the appointment of a receiver, trustee, custodian, sequestrator,
     conservator or similar official for Chiron, Diagnostics or any of their
     Significant U.S. Subsidiaries or for a substantial part of the property or
     assets of Chiron, Diagnostics or any of their Significant U.S.
     Subsidiaries, or (iii) the winding-up or liquidation of chiron, 
     Diagnostics or any of their significant U.S. Subidiaries, and such 
     proceeding  or petition is not dismissed within 60 days or an order 
     for relief is entered against Diagnostics, Chiron or such Significant 
     U.S. Subsidiary, as applicable;

          (e) Chiron or its subsidiaries (except Diagnostics and its
     subsidiaries) shall fail collectively to own

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     more than 50% of the voting stock of Diagnostics or any successor entity;
     and

          (f) Chiron, Diagnostics or any of their Significant U.S. Subsidiaries
     shall (i) voluntarily commence any proceeding or file any petition seeking
     relief under Title 11 of the United States Code, as now constituted or
     hereafter amended, or any other Federal or state bankruptcy, insolvency,
     receivership or similar law, (ii) consent to the institution of, or fail to
     contest in a timely and appropriate manner, any proceeding or the filing of
     any petition described in (d) above, (iii) apply for or consent to the
     appointment of a receiver, trustee, custodian, sequestrator, conservator or
     similar official for Chiron, Diagnostics or any of their Significant U.S.
     Subsidiaries or for a substantial part of the property or assets of Chiron,
     Diagnostics or any of their Significant U.S. Subsidiaries, (iv) file an
     answer admitting the material allegations of a petition filed against it in
     any such proceeding, (v) make a general assignment for the benefit of
     creditors, (vi) become unable, admit in writing its inability or fail
     generally to pay its debts as they become due or (vii) take any action for
     the purpose of effecting any of the foregoing;

then, and in every such event (other than an event with respect to Chiron,
Diagnostics or any of their Significant U.S. Subsidiaries described in paragraph
(d) or (f) above), and at any time thereafter during the continuance of such
event, Ciba may, by notice to Diagnostics, take the following action:  declare
any and all principal or interest (and any other amounts) then outstanding to be
forthwith due and payable in whole or in part, whereupon the principal of this
Note so declared to be due and payable, together with accrued interest thereon
(and any other amounts), shall become forthwith due and payable, without
presentment, demand, protest or any other notice of any kind, all of which are
hereby expressly waived by Diagnostics, anything contained herein to the
contrary notwithstanding; and in any event with respect to Diagnostics described
in paragraph (d) or (f) above, the principal then outstanding, together with
accrued interest thereon (and any other amounts), shall automatically become due
and payable, without presentment, demand, protest or any other notice of any
kind, all of which are expressly waived by Diagnostics, anything contained
herein to the contrary notwithstanding.

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DEFINITIONS

          "BUSINESS DAY" shall mean any day (other than a day which is a
Saturday, Sunday or legal holiday in the State of New York) on which banks are
open for business in New York City.

          "LIBOR" shall mean, with respect to any calendar quarter, the
arithmetic mean of the offered rates for deposits in U.S. dollars for a
principal amount closest to the principal amount outstanding at such time under
this Note for a period of 90 days which appear on the Reuters Screen LIBO Page
(on the Reuter Monitor Money Rate Service) as of 11:00 a.m., London time, on the
day that is two London banking days prior to the commencement of such calendar
quarter.

          "LIEN" shall mean, with respect to any asset, any mortgage, lien,
pledge, charge, security interest or encumbrance of any kind in respect of such
asset.  For the purposes of this Note, Diagnostics or any subsidiary of
Diagnostics shall be deemed to own subject to a Lien any asset which it has
acquired or holds subject to the interest of a vendor or lessor under any
conditional sale agreement, capital lease or other title retention agreement
relating to such asset.

          "SIGNIFICANT U.S. SUBSIDIARY" shall mean, with respect to any person,
any subsidiary of such person that constitutes a significant subsidiary within
the meaning of Rule 1-02 of Regulation S-X promulgated by the Securities and
Exchange Commission and that is a U.S. subsidiary of such person.

          This note has been amended and restated in the form hereof in order to
adjust the principal amount hereof.  Notwithstanding such amendment and
restatement, this Note is made on and as of the date first above written and all
references in this Note to its date shall refer to such above written date.

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          This Note shall be construed in accordance with and governed by the
laws of the State of New York.


                                             CIBA CORNING DIAGNOSTICS
                                             CORP.,



                                             by  Robert L. Sullivan
                                                 ----------------------
                                                 Name:  Robert L. Sullivan
                                                 Title: Senior Vice President

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                                    Payments
                                    --------

Payments                 Payments                           Name of Person
of                       of                                 Making
Principal                Interest            Date           Notation
---------                --------            ----           --------