SEC 1745
(02-02)

Potential persons who are to respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number.

UNITED STATES

OMB APPROVAL

SECURITIES AND EXCHANGE COMMISSION

OMB Number:
3235-0145

Washington, D.C. 20549

Expires: December 31, 2005

SCHEDULE 13G

Estimated average burden hours per response. . 11

[     ]

Rule 13d-1(b)

[ X ]

Rule 13d-1(c)

[     ]

Rule 13d-1(d)

CUSIP No. 

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Aventis Pharmaceuticals Inc. 13-2563649

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

[     ]

(b)

[     ]

3.

SEC Use Only

4.

Citizenship or Place of Organization
Delaware

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
2,799,552 (1)

6.

Shared Voting Power
0

7.

Sole Dispositive Power
2,799,552 (1)

8.

Shared Dispositive Power
0

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
2,799,552 (1)

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  [     ]

11.

Percent of Class Represented by Amount in Row (9)
5.3% (3)

12.

Type of Reporting Person (See Instructions)
CO

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Aventis Holdings Inc. 51-0414396

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

[     ]

(b)

[     ]

3.

SEC Use Only

4.

Citizenship or Place of Organization
Delaware

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
2,799,552 (2)

6.

Shared Voting Power
0

7.

Sole Dispositive Power
2,799,552 (2)

8.

Shared Dispositive Power
0

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
2,799,552 (2)

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  [     ]

11.

Percent of Class Represented by Amount in Row (9)
5.3% (3)

12.

Type of Reporting Person (See Instructions)
CO

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Aventis Inc. 23-1699163

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

[     ]

(b)

[     ]

3.

SEC Use Only

4.

Citizenship or Place of Organization
Pennsylvania

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
2,799,552 (2)

6.

Shared Voting Power
0

7.

Sole Dispositive Power
2,799,552 (2)

8.

Shared Dispositive Power
0

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
2,799,552 (2)

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  [     ]

11.

Percent of Class Represented by Amount in Row (9)
5.3% (3)

12.

Type of Reporting Person (See Instructions)
CO

Item 1.

(a)

Name of Issuer
Regeneron Pharmaceuticals Inc.

(b)

Address of Issuer’s Principal Executive Offices
777 Old Saw Mill River Road
Tarrytown, NY  10591-6707

Item 2.

(a)

Name of Person Filing

(b)

Address of Principal Business Office or, if none, Residence

(c)

Citizenship

(a) - (c)  This Schedule is filed on behalf of Aventis Pharmaceuticals Inc. (“API”) with a principal place of business and principal office located at 300 Somerset Corporate Boulevard, Bridgewater, New Jersey 08807.  API is an indirect subsidiary of Aventis S.A., a French corporation (“Aventis”) headquartered in Strasbourg, France.

This Schedule also is filed on behalf of Aventis Holdings Inc., a Delaware corporation (“AHI”), which owns a 100% of the equity of API.  AHI also is an indirect subsidiary of Aventis.  The principal place of business and principal office of AHI is 3711 Kenneth Pike, Suite 200 Greenville, Delaware 19801. AHI is filing this Schedule solely with respect to its potential deemed indirect ownership of the Issuer’s stock owned by API.

This Schedule also is filed on behalf of Aventis Inc., a Pennsylvania corporation (“AI”), which owns 100% of the equity of AHI.  100% of the equity of AI is held by Aventis, a portion of which is held directly and a portion of which is held indirectly.  The principal place of business and principal office of AI is 300 Somerset Corporate Boulevard, Bridgewater, New Jersey 08807. AI is filing this Schedule solely with respect to its potential deemed indirect ownership of the Issuer’s stock owned by API.

(d)

Title of Class of Securities
Common Stock, $.001

(e)

CUSIP Number
75886F107

Item 3.

If this statement is filed pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

Not Applicable

(a)

[  ]

Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).

(b)

[  ]

Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).

(c)

[  ]

Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c).

(d)

[  ]

Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8).

(e)

[  ]

An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);

(f)

[  ]

An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);

(g)

[  ]

A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);

(h)

[  ]

A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i)

[  ]

A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

(j)

[  ]

Group, in accordance with §240.13d-1(b)(1)(ii)(J).

Item 4.

Ownership

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

(a)

Amount beneficially owned:    2,799,552 Shares Of Common Stock.

(b)

Percent of class:    5.3%

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote    2,799,552

(ii)

Shared power to vote or to direct the vote    0

(iii)

Sole power to dispose or to direct the disposition of    2,799,552

(iv)

Shared power to dispose or to direct the disposition of    0

Item 5.

Ownership of Five Percent or Less of a Class

Not Applicable

Item 6.

Ownership of More than Five Percent on Behalf of Another Person

Not Applicable

Item 7.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person

Not Applicable

Item 8.

Identification and Classification of Members of the Group

Not Applicable

Item 9.

Notice of Dissolution of Group

Not Applicable

Item 10.

Certification

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

AVENTIS PHARMACEUTICALS INC.

Date:

September 12, 2003

By:

/s/ Pascal Soriot

Pascal Soriot

President

AVENTIS HOLDINGS INC.

Date:

September 12, 2003

By:

/s/ Joseph M. Palladino

Joseph M. Palladino

President

AVENTIS INC.

Date:

September 12, 2003

By:

/s/ Gerald P. Belle

Gerald P. Belle

President