-


                      SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C. 20549

                            ----------------------

                                 SCHEDULE 13D

                   UNDER THE SECURITIES EXCHANGE ACT OF 1934
                              (AMENDMENT NO. 13)*

                            ----------------------

                              CHIRON CORPORATION

------------------------------------------------------------------------------
                               (Name of Issuer)


                    COMMON STOCK, PAR VALUE $0.01 PER SHARE

------------------------------------------------------------------------------
                          (Title of Class of Securities)

                                   170040109
------------------------------------------------------------------------------



                      (CUSIP Number of Class of Securities)

      Wayne P. Merkelson                       Andrew R. Brownstein, Esq.
      Novartis Corporation                     Trevor S. Norwitz, Esq.
      608 Fifth Avenue                         Wachtell, Lipton, Rosen & Katz
      New York, New York 10020                 51 West 52 Street
      (212) 307-1122                           New York , New York 10019
                                               (212) 403-1000
------------------------------------------------------------------------------
               (Name, Address and Telephone Number of Person
         Authorized to Receive Notices and Communications on Behalf of
                                 Filing Persons)


                                 DECEMBER 8, 2005
------------------------------------------------------------------------------
           (Date of Event Which Requires Filing of this Statement)


      If the filing person has previously filed a statement on
      Schedule 13G to report the acquisition that is the subject of this
      Schedule 13D, and is filing this schedule because of
      ss240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following
      box. |_|

      NOTE: Schedules filed in paper format shall include a signed
      original and five copies of the schedule, including all exhibits.
      See s240.13d-7 for other parties to whom copies are to be sent.


      *The remainder of this cover page shall be filled out for a
      reporting person's initial filing on this form with respect to the
      subject class of securities, and for any subsequent amendment
      containing information which would alter disclosures provided in a
      prior cover page.

                                      -1-



      The information required on the remainder of this cover page shall
      not be deemed to be "filed" for the purpose of Section 18 of the
      Securities Exchange Act of 1934 ("Act") or otherwise subject to the
      liabilities of that section of the Act but shall be subject to all
      other provisions of the Act (however, see the Notes).
------------------------------------------------------------------------------



















                                        -2-



CUSIP No. 170040109
------------------------------------------------------------------------------

   1.   NAMES OF REPORTING PERSONS:
        Novartis Biotech Partnership, Inc.
    
        I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY):
        06-1415318
        ----------------------------------------------------------------------

   2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS):

        (a)   |_|
              ----------------------------------------------------------------

        (b)   |_|
              ----------------------------------------------------------------

   3.   SEC USE ONLY:

        ----------------------------------------------------------------------

   4.   SOURCE OF FUNDS (SEE INSTRUCTIONS):
        AF
        ----------------------------------------------------------------------
 
   5.   CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT 
        TO ITEMS 2(d) OR 2(e)              |_|
        ----------------------------------------------------------------------
 
   6.   CITIZENSHIP OR PLACE OF ORGANIZATION
        Delaware
        ----------------------------------------------------------------------
 
Number of    7. SOLE VOTING POWER
Shares          0
Beneficially     --------------------------------------------------------------
Owned by
Each   
Reporting    8. SHARED VOTING POWER
Person          128,057,488
With            --------------------------------------------------------------


                                       -3-




              9. Sole Dispositive Power
                 0
                 -------------------------------------------------------------
         
             10. Shared Dispositive Power
                 128,057,488
                 -------------------------------------------------------------

 11.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
       128,057,488
       -----------------------------------------------------------------------
 
 12.   CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN 
       SHARES (SEE INSTRUCTIONS)                                       |_|
       -----------------------------------------------------------------------
 
 13.   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
       52.7%
       -----------------------------------------------------------------------
 
 14.   TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
       CO 
       -----------------------------------------------------------------------


                                      -4-



CUSIP No.  170040109
------------------------------------------------------------------------------

   1.   NAMES OF REPORTING PERSONS:
        Novartis Corporation
    
        I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY):
        13-1834433
        ----------------------------------------------------------------------

   2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS):

        (a)   |_|
              ----------------------------------------------------------------

        (b)   |_|
              ----------------------------------------------------------------

   3.   SEC USE ONLY:

        ----------------------------------------------------------------------

   4.   SOURCE OF FUNDS (SEE INSTRUCTIONS):
        AF
        ----------------------------------------------------------------------
 
   5.   CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT 
        TO ITEMS 2(d) OR 2(e)              |_|
        ----------------------------------------------------------------------
 
   6.   CITIZENSHIP OR PLACE OF ORGANIZATION
        New York
        ----------------------------------------------------------------------
 
Number of    7. SOLE VOTING POWER
Shares          0
Beneficially     --------------------------------------------------------------
Owned by
Each   
Reporting    8. SHARED VOTING POWER
Person          128,064,944
With            --------------------------------------------------------------

                                        -5-




              9. Sole Dispositive Power
                 0
                 -------------------------------------------------------------
         
             10. Shared Dispositive Power
                 128,064,944
                 -------------------------------------------------------------

 11.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
       128,064,944
       -----------------------------------------------------------------------
 
 12.   CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN 
       SHARES (SEE INSTRUCTIONS)            |_|
       -----------------------------------------------------------------------
 
 13.   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
       52.7%
       -----------------------------------------------------------------------
 
 14.   TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
       CO 
       -----------------------------------------------------------------------


                                   -6-




CUSIP No.  170040109
-----------------------------------------------------------------------------
 
-----------------------------------------------------------------------------

   1.   NAMES OF REPORTING PERSONS:
        Novartis Pharma AG

        I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY):

        ----------------------------------------------------------------------

   2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS):

        (a)   |_|
              ----------------------------------------------------------------

        (b)   |_|
              ----------------------------------------------------------------

   3.   SEC USE ONLY:

        ----------------------------------------------------------------------

   4.   SOURCE OF FUNDS (SEE INSTRUCTIONS):
        WC
        ----------------------------------------------------------------------
 
   5.   CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT 
        TO ITEMS 2(d) OR 2(e)              |_|
        ----------------------------------------------------------------------
 
   6.   CITIZENSHIP OR PLACE OF ORGANIZATION
        Switzerland
        ----------------------------------------------------------------------
 
Number of    7. SOLE VOTING POWER
Shares          0
Beneficially     --------------------------------------------------------------
Owned by
Each   
Reporting    8. SHARED VOTING POWER
Person          5,469,770
With            --------------------------------------------------------------

                                        -7-



              9. Sole Dispositive Power
                 0
                 -------------------------------------------------------------
         
             10. Shared Dispositive Power
                 5,469,770
                 -------------------------------------------------------------

 11.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
       5,469,770
       -----------------------------------------------------------------------
 
 12.   CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN 
       SHARES (SEE INSTRUCTIONS)            |_|
       -----------------------------------------------------------------------
 
 13.   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
       2.3%
       -----------------------------------------------------------------------
 
 14.   TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
       CO 
       -----------------------------------------------------------------------


                                        -8-



CUSIP No.  170040109
------------------------------------------------------------------------------
 
------------------------------------------------------------------------------


   1.   NAMES OF REPORTING PERSONS:
        Novartis AG

        I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY):

        ----------------------------------------------------------------------

   2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS):

        (a)   |_|
              ----------------------------------------------------------------

        (b)   |_|
              ----------------------------------------------------------------

   3.   SEC USE ONLY:

        ----------------------------------------------------------------------

   4.   SOURCE OF FUNDS (SEE INSTRUCTIONS):
        WC
        ----------------------------------------------------------------------
 
   5.   CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT 
        TO ITEMS 2(d) OR 2(e)              |_|
        ----------------------------------------------------------------------
 
   6.   CITIZENSHIP OR PLACE OF ORGANIZATION
        Switzerland
        ----------------------------------------------------------------------
 
Number of    7. SOLE VOTING POWER
Shares          0
Beneficially     --------------------------------------------------------------
Owned by
Each   
Reporting    8. SHARED VOTING POWER
Person          133,527,258
With            --------------------------------------------------------------


                                   -9-



              9. Sole Dispositive Power
                 0
                 -------------------------------------------------------------
         
             10. Shared Dispositive Power
                 133,527,258
                 -------------------------------------------------------------

 11.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
       133,527,258
       -----------------------------------------------------------------------
 
 12.   CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN 
       SHARES (SEE INSTRUCTIONS)            |_|
       -----------------------------------------------------------------------
 
 13.   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
       55%
       -----------------------------------------------------------------------
 
 14.   TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
       CO 
       -----------------------------------------------------------------------


                                        -10-



ITEM 1.  SECURITY AND ISSUER


      This Amendment No. 13 to Schedule 13D relates to Common Stock, par
value $0.01 per share (the "Common Stock"), of Chiron Corporation, a
Delaware corporation (the "Company"). Novartis AG ("Novartis"), Novartis
Corporation, ("Novartis Corp"), Novartis Biotech Partnership, Inc.
("Biotech"), and Novartis Pharma AG ("Novartis Pharma" and, together with
Novartis, Novartis Corp and Biotech the "Reporting Persons") hereby
amend the Schedule 13D.


ITEM 3.  SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION

      Item 3 is hereby amended and supplemented by adding the following:

      Novartis financed the transactions described in Item 4 below through the
issuance of short-term commercial paper.

ITEM 4.  PURPOSE OF TRANSACTION

      Item 4 is hereby amended and supplemented by adding the following:

      (a)  On October 30, 2005, the Company gave Novartis and Novartis Corp
notice of the exercise of its right, pursuant to the Subscription Agreement,
dated as of November 20, 1994, among the Company, Novartis and certain of its
affiliates, (filed as an exhibit to the Schedule 13D on January 21, 1997), to
require Biotech to purchase an aggregate of $300,000,000 worth of shares of
Common Stock at $43.50 per share directly from the Company.  Pursuant to that
notice, on December 8, 2005, Novartis Biotech completed the purchase of
6,896,552 shares of Common Stock from Chiron for $43.50 per share, resulting
in an aggregate purchase price of $300,000,012.

ITEM 5.  INTEREST IN SECURITIES OF ISSUER

      Items 5(a) and 5(b) are hereby amended in their entirety as follows:

      (a) and (b) As of the date of this Amendment, Biotech is the record
holder of 80,739,404 shares of Common Stock, including the 6,896,552 shares
of Common Stock described in Item 4(a) above.  In addition, pursuant to the
Market Price Option Agreement, Biotech or its designee, which must be
Novartis or a subsidiary thereof, has the right to purchase from the Company
under certain circumstances such number of shares of Common Stock as are
necessary for the Reporting Persons to maintain collectively up to a 55%
ownership interest in the Company, which as of October 31, 2005, constituted
the right to purchase an additional 47,318,084 shares, based on 195,472,305
shares of Common Stock outstanding at October 31, 2005, as reported in the
Company's Preliminary Proxy Statement filed with the Securities and Exchange
Commission on November 25, 2005. Biotech is the beneficial owner of
128,057,488 shares of Common Stock, or 55% of the Common Stock, assuming
Biotech exercises its right to purchase the additional shares of Common Stock
pursuant to Market Price Option Agreement. Biotech has shared power to vote
or to direct the vote and shared power to dispose or to direct the
disposition with respect to all the shares of Common Stock beneficially owned
by it.

       Novartis Corp is the record holder of 7,456 shares of Common Stock.
After adjusting the total number of shares beneficially owned by Novartis
Corp to include the 128,057,488 shares beneficially owned by Biotech,
Novartis Corp is the beneficial owner of 128,064,944 shares of Common Stock or
52.7% of the Common Stock, assuming Biotech exercises its right to purchase
the additional shares of Common Stock pursuant to Market Price Option
Agreement. Novartis Corp has shared power to vote or to direct the vote and
shared power to dispose or to direct the disposition with respect to all the
shares of Common Stock beneficially owned by it.

      Novartis Pharma is the record holder of 5,469,770 shares of Common
Stock, or 2.3% of the Common Stock, assuming Biotech exercises its right to
purchase the additional shares of Common Stock 

                                        -11-




pursuant to Market Price Option Agreement. Novartis Pharma has shared power 
to vote or to direct the vote and shared power to dispose or to direct the 
disposition with respect to all the shares of Common Stock beneficially owned 
by it.

      Novartis is the beneficial owner of the shares of Common Stock
beneficially owned by Novartis Pharma, Novartis Corp and Biotech. Novartis
beneficially owns 133,534,714 shares of Common Stock, giving it a 55%
beneficial interest in the Company, assuming Biotech exercises its right to
purchase the additional shares of Common Stock pursuant to Market Price
Option Agreement. Novartis has shared power to vote or to direct the vote and
shared power to dispose or to direct the disposition of the shares of Common
Stock beneficially owned by Biotech, Novartis Corp and Novartis Pharma.

      To the best knowledge of each of the Reporting Persons, none of the
persons listed on Schedule I hereto with respect to such Reporting Person is
the beneficial owner of any shares of Common Stock, other than Raymund Breu,
who is the beneficial owner of 55,666 shares of Common Stock.


ITEM 7.  MATERIAL TO BE FILED AS EXHIBITS

      99.1   Joint Filing Agreement, by and among Novartis Biotech Partnership,
             Inc., Novartis Corporation, Novartis Pharma AG and Novartis AG,
             dated as of December 12, 2005.

                                        -12-




                                     SIGNATURES


      After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete
and correct.

Dated: December 12, 2005       
                                
                                
                               NOVARTIS BIOTECH PARTNERSHIP, INC.
                                
                                
                               By:/s/ Wayne P. Merkelson              
                                  --------------------------------------
                                  Name: Wayne P. Merkelson
                                  Title: Vice President

                                
                               NOVARTIS CORPORATION
                                
                                
                               By:/s/ Jeff Benjamin             
                                  --------------------------------------
                                  Name: Jeff Benjamin
                                  Title: Vice President and General Counsel
                                
                                
                               NOVARTIS PHARMA AG
                                
                                
                               By:/s/ Dr. Ingrid Sollerer
                                  --------------------------------------
                                  Name:  Dr. Ingrid Sollerer
                                  Title: Authorized Signatory

                               By:/s/ Dr. Peter Kornicker
                                  --------------------------------------
                                  Name:  Dr. Peter Kornicker
                                  Title: Authorized Signatory


                               NOVARTIS AG


                                By:/s/ Peter Rupprecht
                                  --------------------------------------
                                  Name:  Peter Rupprecht
                                  Title: Authorized Signatory

                                By:/s/ Urs Baerlocher
                                  --------------------------------------
                                  Name:  Urs Baerlocher
                                  Title: Authorized Signatory





                                 Exhibit Index


-----------------------------------------------------------------------------
 EXHIBIT NUMBER                    EXHIBIT NAME
 --------------                    ------------
-----------------------------------------------------------------------------
   99.1              Joint Filing Agreement, by and among Novartis
                     Biotech Partnership, Inc., Novartis
                     Corporation, Novartis Pharma AG and Novartis
                     AG, dated as of December 12, 2005.
-----------------------------------------------------------------------------

                                        -14-




                                                                   Exhibit 99.1

                            JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k)(1) under the Securities Exchange Act of
1934, as amended, the undersigned hereby agree that this Statement on
Schedule 13D with respect to the beneficial ownership of shares of Common
Stock of Chiron Corporation is filed jointly, on behalf of each of them.
This Agreement may be executed in any number of counterparts, all of which
taken together shall constitute one and the same instrument.

Dated:  December 12, 2005

                               NOVARTIS BIOTECH PARTNERSHIP, INC.

                               By: /s/ Wayne P. Merkelson
                                  --------------------------------------
                               Name: Wayne P. Merkelson
                               Title: Vice President

                               NOVARTIS CORPORATION

                               By: /s/ Jeff Benjamin
                                  --------------------------------------
                               Name: Jeff Benjamin
                               Title: Vice President and General Counsel

                               NOVARTIS PHARMA AG

                               By: /s/  Dr. Ingrid Sollerer
                                  --------------------------------------
                               Name:   Dr. Ingrid Sollerer
                               Title:  Authorized Signatory

                               By: /s/  Dr. Peter Kornicker         
                                  --------------------------------------
                               Name:   Dr. Peter Kornicker
                               Title:  Authorized Signatory

                               NOVARTIS AG

                               By: /s/  Peter Rupprecht    
                                  --------------------------------------
                               Name:   Peter Rupprecht
                               Title:  Authorized Signatory

                               By: /s/ Urs Baerlocher
                                  --------------------------------------
                               Name:   Urs Baerlcoher
                               Title:  Authorized Signatory