Ownership Submission
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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(Print or Type Responses)
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)
04/18/2006
(Street)

EMERYVILLE, CA 94608		 4. If Amendment, Date Original Filed(Month/Day/Year)
 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 04/18/2006   M   2,812 A $ 19.4375 16,960 D  
Common Stock 04/18/2006   S   2,812 D $ 47.95 14,148 D  
Common Stock 04/18/2006   M   20,000 A $ 43.8125 34,148 D  
Common Stock 04/18/2006   S   20,000 D $ 47.95 14,148 D  
Common Stock 04/18/2006   M   20,000 A $ 45.7188 34,148 D  
Common Stock 04/18/2006   S   20,000 D $ 47.95 14,148 D  
Common Stock 04/18/2006   M   10,000 A $ 44.84 24,148 D  
Common Stock 04/18/2006   S   10,000 D $ 47.95 14,148 D  
Common Stock 04/18/2006   M   15,000 A $ 42.535 29,148 D  
Common Stock 04/18/2006   S   15,000 D $ 47.95 14,148 D  
Common Stock 04/18/2006   M   11,563 A $ 36.335 25,711 D  
Common Stock 04/18/2006   S   11,563 D $ 47.95 14,148 D  
Common Stock 04/18/2006   M   15,573 A $ 33.88 29,721 D  
Common Stock 04/18/2006   S   15,573 D $ 47.95 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) $ 19.4375 04/18/2006   M     2,812 02/19/1999(1) 02/18/2008 Common Stock 2,812 (2) 0 D  
Employee Stock Option (Right to Buy) $ 43.8125 04/18/2006   M     20,000 01/02/2002(3) 01/01/2011 Common Stock 20,000 (2) 5,000 D  
Employee Stock Option (Right to Buy) $ 45.7188 04/18/2006   M     20,000 02/16/2002(4) 02/15/2011 Common Stock 20,000 (2) 0 D  
Employee Stock Option (Right to Buy) $ 44.84 04/18/2006   M     10,000 01/11/2003(5) 01/10/2012 Common Stock 10,000 (2) 15,000 D  
Employee Stock Option (Right to Buy) $ 42.535 04/18/2006   M     15,000 02/21/2003(6) 02/20/2012 Common Stock 15,000 (2) 0 D  
Employee Stock Option (Right to Buy) $ 36.335 04/18/2006   M     11,563 02/20/2004(7) 02/19/2013 Common Stock 11,563 (2) 3,437 D  
Employee Stock Option (Right to Buy) $ 33.88 04/18/2006   M     15,573 02/22/2006(8) 02/21/2015 Common Stock 15,573 (9) 41,927 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   04/19/2006
**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) The option was originally granted for 15,000 shares on February 19, 1998. 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.
(2) Employee Stock Option granted under the Issuer's 1991 Stock Option Plan in a transaction exempt under Rule 16b-3(d).
(3) The option was originally granted for 25,000 shares on January 2, 2001. The option vests after seven years of service with the Issuer or upon earlier achievement of specified performance objectives. Certain performance objectives were achieved during the initial three-year period measured from the grant date, and the option accordingly vested in part and became exercisable as follows: 5,000 shares on January 2, 2002; 5,000 shares on January 2, 2003; and 10,000 shares on January 2, 2004. The option will vest and become exercisable for the balance of the option shares upon the Reporting Person's completion of seven years of service with the Issuer or upon earlier achievement of specified performance objectives.
(4) The option was originally granted for 20,000 shares on February 16, 2001. 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.
(5) The option was originally granted for 25,000 shares on January 2, 2001. The option vests after seven years of service with the Issuer or upon earlier achievement of specified performance objectives. Certain performance objectives were achieved during the initial two-year period measured from the grant date, and the option accordingly vested in part and became exercisable as follows: 2,500 shares on January 11, 2003 and 7,500 shares on January 11, 2004. The option will vest and become exercisable for the balance of the option shares upon the Reporting Person's completion of seven years of service with the Issuer or upon earlier achievement of specified performance objectives.
(6) The option was originally granted for 15,000 shares on February 21, 2002. 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.
(7) The option was originally granted for 15,000 shares on February 20, 2003. The option vested and became exercisable for one-fourth of the total shares on the first anniversary of the grant date and vests and becomes 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.
(8) The option was originally granted for 57,500 shares on February 22, 2005. The option vested and became exercisable for one-fourth of the total shares on the first anniversary of the grant date and vests and becomes 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.
(9) Employee Stock Option granted under the Issuer's 2004 Stock Compensation Plan in a transaction exempt under Rule 16b-3(d).

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