As filed with the Securities and Exchange Commission on September 12, 2005

Registration No. 333-92383

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

POST-EFFECTIVE AMENDMENT NO. 3 TO
FORM S-1 ON FORM S-3
REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

CHARLES RIVER LABORATORIES INTERNATIONAL, INC.

(Exact name of registrant as specified in its charter)

Approximate date of commencement of proposed sale to the public: from time to time after the effective date.

If the only securities being registered on this form are being offered pursuant to dividend or interest reinvestment plans, please check the following box.  o

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box.  ý

If this form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  o

If this form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ý
333-92383

If delivery of the prospectus is expected to be made pursuant to Rule 434, please check the following box.  o

EXPLANATORY NOTE

We initially issued the warrants in a transaction exempt from the registration requirements of the Securities Act of 1933. Each warrant entitles the holder to purchase 7.60 shares of our common stock at an exercise price of $5.19 per share, subject to adjustment in some circumstances. We filed a registration statement (Registration No. 333-92383) in order to permit the holders of these warrants and shares of our common stock acquired on exercise of these warrants to resell those securities in transactions that are registered under the Securities Act of 1933.

This Post-Effective Amendment No. 3 to Registration Statement on Form S-1 on Form S-3 (File No. 333-92383) is filed solely to add the following additional selling security holders to the table appearing on pages 52 through 55 of the Registration Statement:

None of the above holders has a material relationship with us, except as described in the Registration Statement, as amended.

The contents of the Registration Statement on Form S-1 on Form S-3 (File No. 333-92383) are incorporated by reference herein.

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PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 16.  EXHIBITS

*              Filed herewith.

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SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the Registrant has duly caused this Post-Effective Amendment No. 3 to the Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Wilmington, State of Massachusetts, on the 12th day of September, 2005.

Pursuant to the requirements of the Securities Act of 1933, this Post-Effective Amendment No. 3 to the Registration Statement has been signed by the following persons in the capacities indicated on September 12, 2005.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1933, this Post-Effective Amendment No. 3 to the Registration Statement has been signed by the following persons in the capacities indicated as of September 12, 2005.

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EXHIBIT INDEX

*              Filed herewith.

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