FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person * RAPPUOLI RINO   2. Issuer Name and Ticker or Trading Symbol CHIRON CORP [CHIR] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) V.P., Chief Scientific Officer (Last) (First) (Middle) 4560 HORTON STREET 3. Date of Earliest Transaction (Month/Day/Year) 02/17/2006 (Street) EMERYVILLE, CA 94608 4. If Amendment, Date Original Filed(Month/Day/Year) 02/21/2006 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 02/17/2006   M   11,040 A $ 28.5938 21,090 D   Common Stock 02/17/2006   F   6,942 (1) D $ 45.465 14,148 D

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Employee Stock Option (Right to Buy)

$ 28.5938

02/17/2006

M

11,040

02/23/1997(2)

02/22/2006

Common Stock

11,040

(3)

0

D

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
RAPPUOLI RINO 4560 HORTON STREET EMERYVILLE, CA 94608			V.P., Chief Scientific Officer

Signatures

Rino Rappuoli by Naima Robinson as Atty-in-Fact		02/23/2006
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	These shares were previously acquired by the Reporting Person and delivered to Issuer in satisfaction of both the exercise price and the required withholdings taxes in a transaction exempt under Rule 16b-3(e).
(2)	The option was originally granted for 11,040 shares on February 23, 1996. The option vested and became exercisable for one-fourth of the total shares on the first anniversary of the grant date and vested and became exercisable for the balance of the option shares in a series of thirty-six successive equal monthly installments upon the Reporting Person's completion of each additional month of service with the Issuer thereafter.
(3)	Employee Stock Option granted under the issuer's 1991 Stock Option Plan in transaction exempt under Rule 16b-3.

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