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                       SECURITIES AND EXCHANGE COMMISSION
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                             Washington, D.C. 20549
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                                   SCHEDULE TO
                                 AMENDMENT NO. 4

            TENDER OFFER STATEMENT UNDER SECTION 14(d)(1) or 13(e)(1)
                     OF THE SECURITIES EXCHANGE ACT OF 1934

                                 EON LABS, INC.
                            (Name of Subject Company)

                                   NOVARTIS AG
                              NOVARTIS CORPORATION
                            ZODNAS ACQUISITION CORP.
                       (Name of Filing Persons--Offerors)

                          COMMON STOCK, PAR VALUE $0.01
                         (Title of Class of Securities)

                                    29412E100
                      (CUSIP Number of Class of Securities)

                                  George Miller
                        Head of Legal and General Affairs
                                   Novartis AG
                                 35 Lichtstrasse
                           CH-4002 Basel, Switzerland
                                 41-61-324-1111
            (Name, Address and Telephone Number of Person Authorized
       to Receive Notices and Communications on Behalf of Filing Persons)

                                   -Copies to-
                           Andrew R. Brownstein, Esq.
                             Trevor S. Norwitz, Esq.
                         Wachtell, Lipton, Rosen & Katz
                               51 West 52nd Street
                               New York, NY 10019
                                 (212) 403-1000
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                            CALCULATION OF FILING FEE


          Transaction Valuation                 Amount of Filing Fee
   ------------------------------------- ----------------------------------
   ------------------------------------- ----------------------------------
              $977,098,158*                          $115,005*
   ------------------------------------- ----------------------------------
   ------------------------------------- ----------------------------------

   ------------------------------------- ----------------------------------
*    Estimated for purposes of calculating the amount of the filing fee only.
     The calculation of the filing fee is described on the cover page to
     Amendment No. 1 to the Schedule TO filed on May 27, 2005.
[X]  Check the box if any part of the fee is offset as provided by Rule
     0-11(a)(2) and identify the filing with which the offsetting fee was
     previously paid. Identify the previous filing by registration statement
     number, or the Form or Schedule and the date of its filing.
      Amount Previously Paid:  $115,005          Filing Party:  Novartis Corp.
      Form or Registration No.:  Schedule TO     Date Filed:  May 23, 2005
[ ]  Check the box if the filing relates solely to preliminary communications
made before the commencement of a tender offer. Check the appropriate boxes
below to designate any transactions to which the statement relates: 
[X]  third-party tender offer subject to Rule 14d-1.
[ ]  issuer tender offer subject to Rule 13e-4. 
[ ]  going-private transaction subject to Rule 13e-3. 
[ ]  amendment to Schedule 13D under Rule 13d-2.
Check the following box if the filing is a final amendment reporting the results
of the tender offer: [ ]
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     This Amendment No. 4 amends and  supplements  the Tender Offer Statement on
Schedule  TO,  as  amended,  (the  "Schedule  TO"),  originally  filed  with the
Securities  and  Exchange  Commission  on  May  23,  2005  and  as  amended  and
supplemented  by  Amendment  No. 1 on May 27, 2005,  Amendment  No. 2 on June 2,
2005, and Amendment No. 3 on June 7, 2005, by Novartis AG, a Swiss  Corporation,
Novartis  Corporation  ("Novartis  US"), a New York  corporation and an indirect
wholly owned subsidiary of Novartis AG, and Zodnas Acquisition Corp. ("Zodnas"),
a Delaware  corporation and an indirect wholly owned  subsidiary of Novartis US.
The  Schedule TO relates to the offer by Zodnas to  purchase  any and all of the
outstanding shares of common stock, par value $0.01 per share (the "Shares"), of
Eon Labs, Inc., a Delaware corporation ("Eon"), for $31.00 per Share, net to the
seller in cash,  upon the terms and subject to the  conditions  set forth in the
Offer to  Purchase,  dated May 23,  2005 (the "Offer to  Purchase"),  and in the
related Letter of  Transmittal.  Copies of the Offer to Purchase and the related
Letter of Transmittal  are filed with the Schedule TO as exhibits  (a)(1)(A) and
(a)(1)(B),  respectively.  Capitalized  terms used and not defined  herein shall
have the meanings assigned such terms in the Offer to Purchase and Schedule TO.

ITEMS 1 THROUGH 9 AND 11.

     Items 1 through 9 and 11 of the Schedule TO, which incorporate by reference
the  information  contained  in the Offer to  Purchase,  are hereby  amended and
supplemented as follows:

     The Offer to Purchase is hereby amended and supplemented as follows:

               1.   The  following  sentence  is hereby  added at the end of the
                    second paragraph on page 1:

                    "The  Santo   Purchase  will  be   consummated   immediately
                    following the expiration of the Offer."

               2.   The  following  sentence  is hereby  added at the end of the
                    response to the question on page 6: "Does Purchaser have the
                    financial  resources to pay for the Shares it is offering to
                    purchase?":

                    "No alternative financing plan exists."

               3    In the  response  following  the  question  "If I accept the
                    Offer,  when  will I get  paid?"  on page 7, the  words  "as
                    promptly as  practicable"  are hereby  deleted and  replaced
                    with "promptly".

               4.   The second  sentence of the first  paragraph  in the section
                    entitled  "Forward-Looking  Statements" on page 11 is hereby
                    deleted.

               5.   The following  language is hereby  inserted as an additional
                    paragraph on page 11 following the second  paragraph on such
                    page:






                    "The forward-looking  statements contained within this Offer
                    to Purchase  are not subject to the "safe  harbor"  provided
                    for in  the  Private  Securities  Litigation  Reform  Act of
                    1995."

               6.   The first sentence of the second complete  paragraph on page
                    13 is hereby deleted and replaced with the following:

                    "Novartis US will purchase the Santo Shares  pursuant to the
                    Santo Agreement  immediately following the expiration of the
                    Offer (such purchase, the "Santo Purchase")."

               7.   The  following  sentence  is hereby  added at the end of the
                    third paragraph on page 18:

                    "Neither Novartis AG, Novartis US nor Zodnas has any present
                    intention to transfer or assign, or to cause the transfer or
                    assignment  of, the right to purchase  Shares  tendered into
                    the Offer. In the event of any change in such intention, any
                    transferee  or assignee  will be  considered  an offeror for
                    purposes  of the Offer and will  independently  satisfy  the
                    timing,  signatory  and  dissemination  requirements  of the
                    federal securities laws."

               8.   The  following  words are  inserted  at the end of the third
                    sentence of Section 13 on page 42 and prior to the period:

                    "and no alternative financing plans exist"

               9.   The last paragraph on page 30 is hereby deleted and replaced
                    with the following:


                    The  descriptions  of the  Merger  Agreement  and the  Santo
                    Agreement  in this Offer to Purchase  have been  included to
                    provide you with  information  regarding  their  terms.  The
                    Merger  Agreement  and  the  Santo  Agreement  each  contain
                    representations  and  warranties  made by and to the parties
                    thereto as of specific  dates.  The  statements  embodied in
                    those  representations and warranties were made for purposes
                    of those  contracts  between the respective  parties and are
                    subject  to  qualifications  and  limitations  agreed by the
                    respective  parties in connection with negotiating the terms
                    of those contracts. In addition, certain representations and
                    warranties  were made as of a specified date, may be subject
                    to a  contractual  standard of  materiality  different  from
                    those generally applicable to shareholders, or may have been
                    used  for  the  purpose  of  allocating   risk  between  the
                    respective  parties  rather  than  establishing  matters  as
                    facts.





FORM OF LETTER OF TRANSMITTAL

     The Form of Letter of  Transmittal  included  as Exhibit  (a)(1)(B)  to the
Schedule TO is hereby amended and supplemented as follows:

               1.   The last sentence of the third paragraph on page 5 is hereby
                    deleted and replaced with the following:

                    "Under  certain  circumstances  set  forth  in the  Offer to
                    Purchase,  Purchaser  may  not be  required  to  accept  for
                    payment  any  of the  Shares  tendered  by  this  Letter  of
                    Transmittal."

               2.   The last sentence of the last  paragraph on page 5 is hereby
                    deleted and replaced with the following:

                    "Purchaser  has  no  obligation,  pursuant  to  the  Special
                    Payment  Instructions,  to transfer any Shares from the name
                    of the registered holder(s) of such Shares if Purchaser does
                    not  purchase  any of the Shares  tendered by this Letter of
                    Transmittal."






                                    SIGNATURE

     After due 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:  June 15, 2005
                                              NOVARTIS AG


                                              By: /s/ George Miller     
                                                 -------------------------------
                                                 Name   George Miller
                                                 Title: Authorized Signatory


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


                                              NOVARTIS CORPORATION


                                              By: /s/ Terrence A Barnett        
                                                 -------------------------------
                                                 Name:   Terrence A Barnett
                                                 Title:  President and 
                                                         Chief Executive Officer


                                              ZODNAS ACQUISITION CORP.


                                              By: /s/ Eric Pomerantz            
                                                 -------------------------------
                                                 Name:   Eric Pomerantz
                                                 Title:  Vice President 
                                                         Zodnas Acquistion Corp











                                  EXHIBIT INDEX



*(a)(1)(A) Offer to Purchase, dated May 23, 2005.

*(a)(1)(B) Form of Letter of Transmittal.

*(a)(1)(C) Form of Notice of Guaranteed Delivery.

*(a)(1)(D) Form of Letter to Brokers, Dealers, Commercial Banks, Trust Companies
           and Other Nominees.

*(a)(1)(E) Form of Letter to Clients  for use by  Brokers,  Dealers,  Commercial
           Banks, Trust Companies and Other Nominees.

*(a)(1)(F) Guidelines for Certification of Taxpayer  Identification Number (TIN)
           on Substitute Form W-9.

(a)(2)     Not applicable.

(a)(3)     Not applicable.

(a)(4)     Not applicable.

*(a)(5)(A) Text of Press  Release  issued by Novartis  dated  February 21, 2005,
           incorporated  in this  Schedule TO by reference to the Schedule TO 
           filed by Novartis AG, Novartis US and Zodnas on February 22, 2005.

*(a)(5)(B) Form of Summary Advertisement published in The Wall Street Journal on
           May 23, 2005.

*(a)(5)(C) Text of Press Release issued by Novartis dated May 27, 2005.

*(a)(5)(D) Text of Press Release issued by Novartis dated June 7, 2005.

*(a)(6)(A) Complaint  titled  Ellen Wiehl v. Eon Labs,  Inc.  et al.,  filed on
           February 22, 2005, in the Chancery  Court of the State of Delaware,  
           County of New Castle.

*(a)(6)(B) Complaint titled Paulena Partners LLC v. Eon Labs, Inc. et al., filed
           on February  22,  2005,  in the  Chancery  Court of the State of  
           Delaware, County of New Castle.

*(a)(6)(C) Complaint titled Robert Kemp, IRRA v. Eon Labs, Inc. et al., filed on
           February 22, 2005, in the Chancery  Court of the State of Delaware,  
           County of New Castle.





*(a)(6)(D) Complaint titled Peter J. Calcagno v. Eon Labs, Inc. et al., filed on
           February 23, 2005, in the Chancery  Court of the State of Delaware,  
           County of New Castle.

*(a)(6)(E) Complaint  titled  Christopher  Pizzo v. Novartis AG et al., filed on
           February 23, 2005, in the Supreme Court of the State of New York, 
           County of New York.

*(a)(6)(F) Complaint  titled Erste Sparinvest  Kapitalanlagegesellschaft  MBH v.
           Eon Labs, Inc. et al., filed on March 1, 2005, in the Chancery Court 
           of the State of Delaware, County of New Castle.

*(a)(6)(G) Complaint  titled Merl Huntsinger v. Eon Labs, Inc. et al., filed on
           March 1, 2005,  in the Chancery  Court of the State of Delaware,  
           County of New Castle.

*(a)(6)(H) Complaint  titled Jason Hung v. Eon Labs, Inc. et al., filed on March
           3, 2005,  in the  Chancery  Court of the State of  Delaware,  County 
           of New Castle.

*(a)(6)(I) Consolidated   Amended  Complaint  titled  In  re  Eon  Labs,  Inc.
           Shareholders  Litigation,  filed on May 27, 2005, in the Chancery 
           Court of the State of Delaware, County of New Castle.

(b)        None.

*(d)(1)    Agreement  and Plan of Merger,  dated as of February  20,  2005,  by 
           and among  Novartis  US,  Zodnas,  Eon and,  for purposes of Section 
           12 thereof only, Novartis AG, incorporated in this Schedule TO by 
           reference to Exhibit 2.2 to the  Schedule  13D filed by Novartis  US,
           Novartis AG and Zodnas on March 2, 2005.

*(d)(2)    Agreement for Purchase and Sale of Stock, dated as of February 20, 
           2005, by and between  Novartis  US,  Santo and,  for  purposes  of 
           Section  10.12 thereof only, Novartis AG, incorporated in this 
           Schedule TO by reference to Exhibit  2.1 to the  Schedule  13D filed 
           by  Novartis  US,  Novartis AG and Zodnas on March 2, 2005.

*(d)(3)    Confidentiality  Agreement, by and between Novartis US and Eon, dated
           as of February  11,  2005,  incorporated  in this  Schedule TO by 
           reference to Exhibit  2.3 to the Schedule 13D filed by Novartis US,  
           Novartis AG and Zodnas on March 2, 2005.

(g)        None.

(h)        Not applicable.

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* Previously filed.