SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549

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                                  SCHEDULE 13D*
                                 (Rule 13d-101)

             INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT
            TO RULE 13d-1(a) AND AMENDMENTS THERETO FILED PURSUANT TO
                                  RULE 13d-2(a)

                    Under the Securities Exchange Act of 1934
                               (Amendment No. )(1)

                 Charles River Laboratories International, Inc.
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                                (Name of Issuer)

                     Common Stock, $0.01 par value per share
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                         (Title of Class of Securities)

                                    159864107
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                                 (CUSIP Number)

                              Marc Weingarten, Esq.
                            Schulte Roth & Zabel LLP
                                919 Third Avenue
                            New York, New York 10022
                                 (212) 756-2000
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                  (Name, Address and Telephone Number of Person
                Authorized to Receive Notices and Communications)

                                  May 26, 2010
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                          (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 Rule 13d-1(e), 13d-1(f) or 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 Rule 13d-7 for
other parties to whom copies are to be sent.

                         (Continued on following pages)

                               (Page 1 of 6 Pages)

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(1) 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.

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)

- -------------------------- ---------------------- CUSIP NO. 159864107 SCHEDULE 13D PAGE 2 OF 6 PAGES - -------------------------- ---------------------- - ------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY) JANA PARTNERS LLC - ------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) [ ] (b) [ ] - ------------------------------------------------------------------------------- 3 SEC USE ONLY - ------------------------------------------------------------------------------- 4 SOURCE OF FUNDS* AF - ------------------------------------------------------------------------------- 5 CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDING IS REQUIRED PURSUANT TO ITEM 2(d) or 2(e) [ ] - ------------------------------------------------------------------------------- 6 CITIZENSHIP OR PLACE OF ORGANIZATION Delaware - ------------------------------------------------------------------------------- 7 SOLE VOTING POWER 4,657,695 --------------------------------------------------------- NUMBER OF 8 SHARED VOTING POWER SHARES BENEFICIALLY -0- OWNED BY --------------------------------------------------------- EACH 9 SOLE DISPOSITIVE POWER REPORTING PERSON WITH 4,657,695 --------------------------------------------------------- 10 SHARED DISPOSITIVE POWER -0- - ------------------------------------------------------------------------------- 11 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH PERSON 4,657,695 - ------------------------------------------------------------------------------- 12 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES* [ ] - ------------------------------------------------------------------------------- 13 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 7.0% - ------------------------------------------------------------------------------- 14 TYPE OF REPORTING PERSON* IA - ------------------------------------------------------------------------------- * SEE INSTRUCTIONS BEFORE FILLING OUT!

- -------------------------- ---------------------- CUSIP NO. 159864107 SCHEDULE 13D PAGE 3 OF 6 PAGES - -------------------------- ---------------------- Item 1. Security and Issuer. This statement on Schedule 13D relates to the shares ("Shares") of common stock, $0.01 par value per share, of Charles River Laboratories International, Inc., a Delaware corporation (the "Issuer"). The principal executive office of the Issuer is located at 251 Ballardvale Street, Wilmington, Massachusetts 01887. Item 2. Identity and Background. (a) This statement is filed by JANA Partners LLC, a Delaware limited liability company (the "Reporting Person"). The Reporting Person is a private money management firm which holds the Shares of the Issuer in various accounts under its management and control, including but not limited to, 270,182 Shares (the "SP13 Shares") held in Segregated Portfolio 13 ("SP13"), a managed account for which the Reporting Person serves as investment manager. The principals of the Reporting Person are Barry Rosenstein and Gary Claar (the "Principals"). (b) The principal business address of the Reporting Person and the Principals is 767 Fifth Avenue, 8th Floor, New York, New York 10153. (c) The principal business of the Reporting Person and the Principals is investing for accounts under their management. (d) Neither the Reporting Person nor the Principals has, during the last five years, been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors). (e) Neither the Reporting Person nor the Principals has, during the last five years, been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws. (f) The Reporting Person is a limited liability company organized in Delaware. The Principals are citizens of the United States of America. Item 3. Source and Amount of Funds or Other Consideration. The 4,657,695 Shares reported herein by the Reporting Person, were acquired at an aggregate purchase price of approximately $148.7 million. The

- -------------------------- ---------------------- CUSIP NO. 159864107 SCHEDULE 13D PAGE 4 OF 6 PAGES - -------------------------- ---------------------- Shares beneficially owned by the Reporting Person were acquired with investment funds in accounts under management. Item 4. Purpose of Transaction. The Reporting Person acquired the Shares because it believes the Shares are undervalued and represent an attractive investment opportunity. On June 3rd, 2010, representatives of the Reporting Person met with representatives of the Issuer including the Chairman, President & CEO of the Issuer and the Chairman & CEO of WuXi PharmaTech (Cayman) Inc. ("WuXi") in the Reporting Person's offices to discuss the Issuer's proposed acquisition of WuXi. In a letter sent today to the Issuer and attached as Exhibit B, the Reporting Person stated its belief that the proposed WuXi acquisition is suboptimal for the Issuer's shareholders and its intention to vote against the issuance of the Issuer's shares required to complete such acquisition. Except as set forth herein or as would occur upon completion of any of the actions discussed herein, including in any Exhibits hereto, the Reporting Person has no present plan or proposal that would relate to or result in any of the matters set forth in subparagraphs (a)-(j) of Item 4 of Schedule 13D. The Reporting Person intends to review its investment in the Issuer on a continuing basis and may engage in discussions with management, the board of directors, other shareholders of the Issuer and other relevant parties concerning the business, operations, management, board compensation, strategy and future plans of the Issuer. Depending on various factors including, without limitation, the Issuer's financial position and strategic direction, the outcome of the discussions and actions referenced above, actions taken by the board of directors, price levels of the Shares, other investment opportunities available to the Reporting Person, conditions in the securities market and general economic and industry conditions, the Reporting Person may in the future take such actions with respect to its investment in the Issuer as it deems appropriate including, without limitation, purchasing additional Shares or selling some or all of its Shares, engaging in short selling of or any hedging or similar transactions with respect to the Shares and/or otherwise changing its intention with respect to any and all matters referred in Item 4 of Schedule 13D. Item 5. Interest in Securities of the Company. (a) The aggregate percentage of Shares reported to be beneficially owned by the Reporting Person is based upon 66,191,029 Shares outstanding, which is the total number of Shares outstanding as of April 15, 2010 as reported in the Issuer's Quarterly Report on Form 10-Q filed on April 29, 2010 for the period ended March 27, 2010. As of the close of business on June 4, 2010, the Reporting Person may be deemed to beneficially own 4,657,695 Shares constituting approximately 7.0% of the Shares outstanding.

- -------------------------- ---------------------- CUSIP NO. 159864107 SCHEDULE 13D PAGE 5 OF 6 PAGES - -------------------------- ---------------------- (b) The Reporting Person has sole voting and dispositive powers over the 4,657,695 Shares, which powers are exercised by the Principals. Notwithstanding the foregoing, pursuant to a Subadvisory Agreement with SP13, in certain circumstances SP13 has the right to override the voting decisions made by the Reporting Person with respect to securities held in SP13, including the SP13 Shares, and has the right to terminate its Subadvisory Agreement with the Reporting Person. (c) Information concerning transaction in the Shares effected by the Reporting Person during the past sixty days is set forth in Appendix A hereto and is incorporated herein by reference. All of the transactions in Shares listed hereto were effected in open market purchases on the New York Stock Exchange through various brokerage entities. (d) No person (other than the Reporting Person) is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Shares. (e) Not applicable. Item 6. Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Company. None. Item 7. Material to be Filed as Exhibits. 1. Exhibit A: Transactions In The Issuer During The Last 60 Days 2. Exhibit B: Letter to James C. Foster dated June 7, 2010

- -------------------------- ---------------------- CUSIP NO. 159864107 SCHEDULE 13D PAGE 6 OF 6 PAGES - -------------------------- ---------------------- 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: June 7, 2010 JANA PARTNERS LLC By: /s/ Jennifer Fanjiang ------------------------- Name: Jennifer Fanjiang Title: Deputy General Counsel

                                    EXHIBIT A

                 TRANSACTIONS IN THE ISSUER IN THE LAST 60 DAYS


Date of Transaction            Shares Purchased (Sold)      Price Per Share ($)
- -------------------            -----------------------      -------------------
5/17/2010                        3,400                            $32.24

5/17/2010                      177,000                            $32.30

5/17/2010                       25,000                            $32.35

5/18/2010                      106,712                            $32.36

5/18/2010                      263,093                            $32.53

5/18/2010                      137,400                            $32.54

5/18/2010                       23,100                            $32.63

5/18/2010                       30,000                            $32.67

5/19/2010                       12,000                            $32.04

5/19/2010                      196,313                            $32.17

5/19/2010                        9,400                            $32.34

5/19/2010                        7,528                            $32.41

5/20/2010                       38,700                            $31.94

5/20/2010                      496,878                            $32.00

5/20/2010                      205,000                            $32.07

5/20/2010                       44,544                            $32.22

5/20/2010                       77,600                            $32.24

5/21/2010                      504,436                            $31.88

5/21/2010                      123,100                            $31.90

5/21/2010                      330,000                            $31.95

5/21/2010                       30,400                            $31.98

5/21/2010                      131,800                            $32.28

5/24/2010                      174,016                            $32.62

5/24/2010                       95,940                            $32.63

5/26/2010                        6,500                            $31.79

5/26/2010                      308,500                            $31.94

5/26/2010                      105,835                            $31.95

5/26/2010                      993,500                            $32.00
                                   EXHIBIT B


June 7, 2010


Mr. James C. Foster
Chairman, President and Chief Executive Officer
Charles River Laboratories International, Inc.
251 Ballardvale Street
Wilmington, Massachusetts 01887


VIA FACSIMILE AND OVERNIGHT DELIVERY

Mr. Foster,

     JANA Partners LLC ("JANA",  "we" or "us") beneficially owns more than 7% of
the  outstanding  shares  of  Charles  River  Laboratories  International,  Inc.
("Charles River" or the "Company") making us the Company's  largest  shareholder
based upon publicly available  information.  We acquired our position because we
believe  Charles  River is  currently  underappreciated  by the market given its
dominant position in the highly defensive research models market, its attractive
valuation on a standalone  basis, the expected  cyclical recovery in preclinical
services  and ongoing  positive  secular  trends in  pharmaceutical  and biotech
outsourcing.  We  appreciated  you  and  Dr.  Ge Li,  Chairman  and  CEO of WuXi
PharmaTech (Cayman) Inc. ("WuXi"),  taking the time to meet with us last week to
discuss the Company's  proposal to acquire WuXi. While we understand your stated
strategic  rationale,  we have serious  doubts about the wisdom of pursuing this
transaction at this time.  Even if the  contemplated  benefits can ultimately be
realized,  we believe  that the high  cost,  significant  integration  risks and
inopportune  timing  simply  make the  proposed  acquisition  the wrong path for
Charles River  shareholders.  For these  reasons,  we intend to vote against the
issuance of Company stock required to complete the proposed acquisition,  and we
believe  based on  shareholder  sentiment  it is likely  that a majority  of the
Company's shareholders will do the same.

     Despite WuXi's valuable assets and well-regarded  chemistry  operation,  we
believe the proposed price, equal to approximately 16x estimated  consensus 2010
EBITDA at  announcement  compared to  approximately  8x for Charles River on the
trading  day  prior  to the  announcement,  cannot  be  justified  given  WuXi's
declining  margins and falling growth rates.  WuXi's gross margins have declined
each year  since  2003 and WuXi  predicts  its gross  margin  will fall again in
2010.(1)  We  believe  these   persistent   margin   declines  are  due  to  the
commoditization of WuXi's core discovery  chemistry  business,  and evidence the
declining  opportunity for labor arbitrage in China.  WuXi's annual sales growth
rate  also  fell  each  year  from  2006  through   2009,   and  the   projected
reacceleration of future growth comes with significant added risk in the face of


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(1)  Gross  profit  adjusted  for   amortization  of  intangibles.


growing competition in its core chemistry business and reliance on growth from its fledgling toxicology business. Despite such trends, the Company's recently filed proxy materials show that the Company and its advisors relied upon what appear to be aggressive WuXi standalone growth and margin assumptions in evaluating the contemplated acquisition and in estimating that it would be neutral to earnings per share in 2011. In fact, analysts have pointed out that even WuXi's own 2010 guidance is below the projections Charles River relied upon in formulating its offer. As Jefferies & Co. analysts have noted, "We believe the credibility of the 2011 and 2012 estimates is low given that 2010 estimates are extremely aggressive compared to [WuXi's] own guidance issued only three weeks ago."(2) Such assumptions for WuXi are also well above consensus, and as Bank of America Merrill Lynch analysts have pointed out would "require sustainable Lab services growth and successful execution in two relatively early stage businesses ([toxicology] and manufacturing) while driving margin expansion in the face of pricing pressure."(3) The proposed acquisition would also pose significant integration risks given the challenges of integrating a new business line located across the globe. As Jefferies & Company analysts recently observed, "Investors must bet against history to believe that [Charles River] can integrate [WuXi] without a stumble, and at over 15x our 2010 EBITDA estimate, [Charles River's] bet is an expensive one."(4) It is also important to note that to finance the proposed transaction Charles River plans to assume significant additional leverage, raising its total debt to EBITDA ratio to 3.3x, further eroding its margin for error in integrating the two businesses. In addition, combining and integrating a broad platform of discovery and preclinical services is a significant distraction at a time when other public contract research organizations ("CROs") have been lowering guidance and Charles Rivers' cyclically weak preclinical business requires increased attention. The timing of the proposed transaction is also highly inopportune for the Company's shareholders. If this acquisition occurs now, WuXi shareholders would walk away with a significantly larger portion of the pro forma entity than if the proposed transaction occurred after the anticipated cyclical recovery when Charles River shares should recover their value. While WuXi may benefit from related cyclical trends as well, discovery services have not suffered declines as severe as preclinical services like toxicology. In any case, as described above Charles River has also already factored in aggressive WuXi growth assumptions in its valuation. Finally with respect to timing, as disclosed in the Company's proxy materials there appear to be no alternate buyers for WuXi, which casts doubt not only on the premium value ascribed to WuXi but also on - ------------------- (2) "Putting on its Marketing Hat", David Windley, Timothy C. Evans, Andrew Hilgenbrink, Ph.D.; Jefferies & Company, Inc., June 2, 2010. (3) "Merger assumptions leave little room for error"; Eric Lo, Eric H. Chang, Bank of America Merrill Lynch, June 2, 2010. (4) "Putting on its Marketing Hat"; David Windley, Timothy C. Evans, Andrew Hilgenbrink, Ph.D.; Jefferies & Company, Inc., June 2, 2010.

why this transaction is necessary now given that there is little risk of losing WuXi to a competitive bidder. Charles River's share price performance in recent years underscores the danger for shareholders of inefficient capital allocation. Despite numerous acquisitions and significant expenditures on new facilities (which in some cases have been temporarily closed shortly after completion) over the years, the Company has significantly and consistently underperformed peers.(5) For example, in 2004 the Company acquired Inveresk Research Group ("Inveresk"), another large transaction which like WuXi was hailed as a "transformational" acquisition and was intended to provide a "broader strategic platform for growth."(6) However, from the trading day before the Inveresk acquisition was announced until the trading day before announcement of the proposed WuXi transaction, the Company's shares declined approximately 19%, compared to an average increase of 108% for its comparably-sized industry peers.(7) After failing to realize the goal of combining early and late stage CRO services, the Company soon divested a significant portion of the assets acquired in the Inveresk transaction and incurred hundreds of millions of dollars in combined write-downs and losses. While smaller tuck-in acquisitions have been more successful, as RW Baird recently noted, "Past acquisitions haven't been [the Company's] strong point, nor have the majority panned out across the industry."(8) While we grasp the theory, we believe that in reality the promised strategic benefits of the contemplated transaction are also far from certain enough to justify the proposed price and timing. As one analyst has noted: "We still see the valuation premium applied as aggressive and the rationale for combination lacking enough supporting evidence to assuage all concerns. We do believe that the combined entity will be competitively differentiated, but we're unconvinced that it will be materially competitively advantaged. We think China is an exciting market, and we believe that a larger presence there is a long-term positive, yet we're unsure of [Charles River's] ability to find synergies between - ------------------- (5) For the one, three and five year periods ending on the trading day prior to the announcement of the WuXi acquisition, the Company's shares have returned approximately 57%, (17)% and (17)%, respectively, compared to 106%, 8% and 110%, respectively, on average for comparably-sized industry peers Covance Inc., Parexel International Corp., ICON plc and Pharmaceutical Product Development Inc., and 46%, (12)% and 17%, respectively, for the S&P 500. All calculations assume reinvestment of dividends. (6) Charles River presentation prepared for joint conference call with Inveresk, July 1, 2004. (7) Such industry peers consist of Covance Inc., Parexel International Corp., ICON plc and Pharmaceutical Product Development Inc. The S&P 500 also outperformed the Company, returning approximately 20%, during the same period. All calculations assume reinvestment of dividends. (8) Charles River Laboratories"; Eric W. Coldwell, Nicholas Juhle; Robert W. Baird & Co., May 12, 2010. Analysts such as UBS Investment Research have expressed similar doubts, noting that "given Charles River's mixed M&A track record (especially the difficulties with the Inveresk acquisition) and the complexity of the WuXi transaction as it relates to combining different business models and corporate cultures, we believe the integration and execution risks are above average." "A Closer Look at the WuXi Acquisition"; Derik de Bruin, Ph.D., Daniel Arlas, Rafael Tejada; UBS Investment Research, May 13, 2010.

the eastern chemistry/manufacturing footprint of [WuXi] and its own western biology business."(9) More broadly, we believe that combining discovery chemistry and biology to create revenue synergies is an untested proposition and may not mesh with how customers currently purchase these services, which at least in some cases are done on a decentralized basis. The Company relies upon a large global sales force with multiple points of customer contact working within a highly regulated framework, making the generation of sales synergies from a combination with WuXi's sales force highly uncertain. It is also worth noting that WuXi is not an unknown provider to pharmaceutical and biotech customers seeking to outsource drug discovery, also casting uncertainty on whether significant revenue synergies can be obtained by a combination. In addition, management's stated intention to leave WuXi's ERP system in place for the foreseeable future (until it can complete its own new ERP systems implementation), rather than rapidly migrating them to the Company's own systems, will likely make sales synergies more difficult to achieve as pricing a bundled offering will be more challenging. Another concern with respect to the proposed strategy is that new and existing customers may demand lower prices for a combined offering, meaning that any potential revenue synergies could be eroded by deterioration in pricing power on the larger components of the combined offering. Such pricing erosion could be exacerbated by the divergent pricing models of Charles River and WuXi.(10) Simply put, we believe that there are much more promising and straightforward means at present to create shareholder value than acquiring a company with decelerating growth prospects and significant integration risks at an expensive valuation using a large amount of the Company's undervalued stock. For example, we note that the Company could employ the same multiple of leverage to trailing EBITDA it would assume in a WuXi acquisition to repurchase approximately 19% of its currently undervalued outstanding shares at a 10% premium to the current Charles River share price, without any integration risk. We believe that a share repurchase of this magnitude would result in accretion to 2011 earnings per share of approximately 14%, and growing thereafter.(11) Based on its history as a leveraged buyout, robust private equity activity in the CRO space and recent published reports, we believe there could be significant private equity interest in the Company, creating potentially - ------------------- (9) "Charles River Laboratories"; Eric W. Coldwell, Nicholas Juhle; Robert W. Baird & Co., May 12, 2010." (10) Bank of America Merrill Lynch for example has expressed concerns regarding "potential cannibalization of sales from having a different pricing model in the US/EU vs. Asia." "Merger assumptions leave little room for error"; Eric Lo, Eric H. Chang; Bank of America Merrill Lynch, June 2, 2010. (11) For purposes of our share repurchase analysis we have made the following assumptions: 1) a share repurchase price of $36.26 (a 10% premium to Charles River's June 4, 2010 closing price of $32.96); 2) 66.2 million shares outstanding as of April 15, 2010 per Charles River's most recent 10-Q; 3) standalone 2011 non-GAAP EPS of $2.70 based on Company guidance for pro forma earnings and expected neutral impact to 2011 earnings from proposed WuXi transaction; 4) total leverage of 3.3x trailing standalone EBITDA and a borrowing cost of 4.5% (consistent with leverage level and borrowing rate of proposed WuXi transaction); 5) termination fee of $25 million (pursuant to acquisition agreement following Company shareholder rejection of the transaction) paid out of excess cash with foregone interest of 1%; and 6) a tax rate on incremental debt and foregone cash interest of 35%.

another means of realizing maximum shareholder value without significant operating or integration risk. Not surprisingly in light of these facts, many Charles River shareholders have already expressed their displeasure with the proposed acquisition by disposing of their stock, which contributed to a share price decline of almost 16% the day the proposed deal was announced. We believe that sentiment among a significant percentage of current shareholders is also decidedly negative.(12) If as appears likely the Company's shareholders reject the proposed WuXi acquisition, we believe the Company is well-positioned for the future and has several attractive options for pursuing future value creation for shareholders, and we are prepared to assist management in exploring such options if we can be of any assistance. In the meantime, we can be reached at (212) 455-0900 should you wish to discuss any of these matters further. Sincerely, /s/ Barry Rosenstein - ----------------------- Barry Rosenstein JANA Partners LLC Managing Partner BR/CP/SO/NM/SA - ------------------- (12) For example, RW Baird noted that "we know that there is a large contingent of shareholders unhappy with the valuation and strategy." "Charles River Laboratories"; Eric W. Coldwell, Nicholas Juhle; Robert W. Baird & Co., May 12, 2010. Wells Fargo reported that, "We fielded multiple calls from investors regarding the deal, and most of them expressed a general disdain." "CRL: Final Thoughts on Q1 2010 And WX Deal"; Greg T. Bolan, Eric Hebert; Wells Fargo Securities, April 26, 2010.