Exhibit 99.1

Charles River Laboratories Reconfirms Guidance; 2003 at High End of
Ranges

    WILMINGTON, Mass.--(BUSINESS WIRE)--Jan. 12, 2004--Charles River
Laboratories' (NYSE:CRL) Chairman, President and Chief Executive
Officer James C. Foster and Senior Vice President and Chief Financial
Officer Thomas F. Ackerman will present on Tuesday, January 13, at the
JPMorgan 22nd Annual Healthcare Conference in San Francisco. In
conjunction with that presentation, and in keeping with the
requirements of SEC Regulation FD, Charles River today confirmed
guidance for 2003 and 2004 as provided in the third-quarter earnings
release on October 29, 2003.
    For 2003, the Company had stated that sales were expected to be 9%
to 11% higher than in 2002 and earnings per diluted share were
expected to be in a range of $1.58 to $1.63. The Company now
anticipates that both sales growth and earnings will be at the high
end of the ranges, due to strength in both business segments.
    The Company also reconfirmed its expectation that for 2004, sales
growth will be in a range of 5% to 9% and earnings per diluted share
will be at least $1.76.
    The Company is planning a reorganization of international
operations in Europe in the first quarter of 2004. The reorganization
would improve operating efficiency and cash management, facilitate
acquisitions and provide tax benefits. If implemented, the
reorganization would result in a one-time, non-cash charge to earnings
in the first quarter, but would improve ongoing earnings and cash flow
in 2004 and thereafter. The reorganization is not included in the
Company's current 2004 guidance.
    Charles River expects to provide further guidance on its
expectations for 2004 in its 2003 fourth-quarter earnings release on
Tuesday, February 10, 2004 and the associated conference call on
Wednesday, February 11 at 8:30 a.m. Eastern time.

    Presentation at JPMorgan Healthcare Conference

    Management will present on Tuesday, January 13, at 10:00 a.m.
Pacific time. A live webcast of the presentation will be available
through a link that will be posted on the Investor Relations section
of the Charles River Laboratories website, http://ir.criver.com. A
webcast replay will be accessible through the Investor Relations
section of the Company's website approximately three hours following
the presentation and will remain available until Tuesday, January 20,
2004. The associated slide presentation will be available for
downloading during that time.
    Charles River Laboratories, based in Wilmington, Massachusetts, is
a leading provider of critical research tools and integrated support
services that enable innovative and efficient drug discovery and
development. The Company is the global leader in providing the animal
research models required in research and development for new drugs,
devices and therapies. The Company also offers a broad and growing
portfolio of biomedical products and services that enable customers to
reduce cost, increase speed, and enhance productivity and
effectiveness in drug discovery and development. Charles River's
customer base spans over 50 countries, and includes all of the major
pharmaceutical companies, biotechnology companies, and many leading
hospitals and academic institutions. The Company operates 82
facilities in 16 countries worldwide.

    Caution Concerning Forward-Looking Statements. This document
includes "forward-looking statements" within the meaning of the
Private Securities Litigation Reform Act of 1995. Forward-looking
statements may be identified by the use of words such as "anticipate,"
"believe," "expect," "estimate," "plan," "outlook," and "project" and
other similar expressions that predict or indicate future events or
trends or that are not statements of historical matters. These
statements are based on management's current expectations, and involve
a number of risks and uncertainties that could cause actual results to
differ materially from those stated or implied by the forward-looking
statements, and the Company expressly does not undertake any duty to
update forward-looking statements, which speak only as of the date of
this document. Those risks and uncertainties include, but are not
limited to: a decrease in pre-clinical research and development
spending or a decrease in the level of outsourced services;
acquisition integration risks; special interest groups;
contaminations; industry trends; new displacement technologies; USDA
and FDA regulations; changes in law; continued availability of
products and supplies; loss of key personnel; interest rate and
foreign currency exchange rate fluctuations; changes in generally
accepted accounting principles; and any changes in business,
political, or economic conditions due to the threat of future
terrorist activity in the U.S. and other parts of the world, and
related U.S. military action overseas. A further description of these
risks, uncertainties, and other matters can be found in the Risk
Factors detailed in the Company's Annual Report on Form 10-K as filed
on March 20, 2003, with the Securities and Exchange Commission.

    CONTACT: Charles River Laboratories
             Investor Contact:
             Susan E. Hardy, 978-658-6000 Ext.1616
             Director, Investor Relations