<PAGE>

                                                                     Exhibit 3.1

                                                                          PAGE 1

                             STATE OF DELAWARE

                     OFFICE OF THE SECRETARY OF STATE

                     --------------------------------

      I, HARRIET SMITH WINDSOR, SECRETARY OF STATE OF THE STATE OF DELAWARE, DO
HEREBY CERTIFY THE ATTACHED ARE TRUE AND CORRECT COPIES OF ALL DOCUMENTS ON FILE
OF "CHARLES RIVER LABORATORIES, INC." AS RECEIVED AND FILED IN THIS OFFICE.

      THE FOLLOWING DOCUMENTS HAVE BEEN CERTIFIED:

      CERTIFICATE OF INCORPORATION, FILED THE TWENTY-FIFTH DAY OF JULY, A.D.
1996, AT 9 O'CLOCK A.M.

      CERTIFICATE OF RENEWAL, FILED THE NINTH DAY OF JULY, A.D. 1999, AT 9
O'CLOCK A.M.

      CERTIFICATE OF AMENDMENT, CHANGING ITS NAME FROM "CHARLES RIVER BRF, INC."
TO "CRL HOLDINGS, INC.", FILED THE NINTH DAY OF JULY, A.D. 1999, AT 9 O'CLOCK
A.M.

      CERTIFICATE OF AMENDMENT, CHANGING ITS NAME FROM "CRL HOLDINGS, INC." TO
"CHARLES RIVER LABORATORIES, INC.", FILED THE THIRTY-FIRST DAY OF AUGUST, A.D.
1999, AT 9 O'CLOCK A.M.

      CERTIFICATE OF MERGER, FILED THE THIRTEENTH DAY OF SEPTEMBER, A.D. 1999,
AT 9 O'CLOCK A.M.

      CERTIFICATE OF MERGER, FILED THE THIRTEENTH DAY OF SEPTEMBER, A.D. 1999,
AT 9:01 O'CLOCK A.M.

      CERTIFICATE OF MERGER, FILED THE THIRTEENTH DAY OF

                               [SEAL]  /s/ Harriet Smith Windsor
                                       -----------------------------------------
                                       HARRIET SMITH WINDSOR, SECRETARY OF STATE

2645754 8100H                                            AUTHENTICATION: 1406279

010529658                                                         DATE: 10-23-01
<Page>

                                                                          PAGE 2

                             STATE OF DELAWARE

                     OFFICE OF THE SECRETARY OF STATE

                     --------------------------------

SEPTEMBER, A.D. 1999, AT 9:02 O'CLOCK A.M.

      CERTIFICATE OF CORRECTION, FILED THE SEVENTEENTH DAY OF SEPTEMBER, A.D.
1999, AT 9 O'CLOCK A.M.

      CERTIFICATE OF OWNERSHIP, FILED THE TWENTY-NINTH DAY OF OCTOBER, A.D.
1999, AT 9 O'CLOCK A.M.

      CERTIFICATE OF OWNERSHIP, FILED THE THIRTIETH DAY OF MARCH, A.D. 2001, AT
3 O'CLOCK P.M.

      CERTIFICATE OF OWNERSHIP, FILED THE TENTH DAY OF APRIL, A.D. 2001, AT 9
O'CLOCK A.M.

      CERTIFICATE OF OWNERSHIP, FILED THE TWENTY-FIFTH DAY OF JULY, A.D. 2001,
AT 4 O'CLOCK P.M.

      AND I DO HEREBY FURTHER CERTIFY THAT THE AFORESAID CERTIFICATES ARE THE
ONLY CERTIFICATES ON RECORD OF THE AFORESAID CORPORATION.

                               [SEAL]  /s/ Harriet Smith Windsor
                                       -----------------------------------------
                                       HARRIET SMITH WINDSOR, SECRETARY OF STATE

2645754 8100H                                            AUTHENTICATION: 1406279

010529658                                                         DATE: 10-23-01
<Page>

                                                           STATE OF DELAWARE
                                                          SECRETARY OF STATE
                                                       DIVISION OF CORPORATIONS
                                                       FILED 09:00 AM 07/25/1996
                                                          960217147 - 2645754

                          CERTIFICATE OF INCORPORATION

                                       of

                             CHARLES RIVER BRF, INC.

      1. The name of this corporation is Charles River BRF, Inc.

      2. The registered office of this corporation in the State of Delaware is
located at 1013 Centre Road, in the City of Wilmington, County of New Castle.
The name of its registered agent at such address is Corporation Service Company.

      3. The purpose of this corporation is to engage in any, lawful act or
activity for which corporations may be organized under the General Corporation
Law of the State of Delaware.

      4. The total number of shares of stock that this corporation shall have
authority to issue is 3,000 shares of Common Stock, $.01 par value per share.
Each share of Common Stock shall be entitled to one vote.

      5. The name and mailing address of the incorporator is: Patrick O'Brien,
Ropes & Gray, One International Place, Boston, Massachusetts 02110.

      6. Except as otherwise provided in the provisions establishing a class of
stock, the number of authorized shares of any class of stock may be increased
or decreased (but not below the number of shares thereof then outstanding) by
the affirmative vote of the holders of a majority of the voting power of the
corporation entitled to vote irrespective of the provisions of Section 242(b)(2)
of the General Corporation Law of the State of Delaware.

      7. The election of directors need not be by written ballot unless the
by-laws shall so require.

      8. In furtherance and not in limitation of the power conferred upon the
board of directors by law, the board of directors shall have power to make,
adopt, alter, amend and repeal from time to time by-laws of this corporation,
subject to the right of the stockholders entitled to vote with respect thereto
to alter and repeal by-laws made by the board of directors.

      9. A director of this corporation shall not be liable to the corporation
or its stockholders for monetary damages for breach of fiduciary duty as a
director, except to the extent that exculpation from liability is not permitted
under the General Corporation Law of the State of Delaware as in effect at the
time such liability is determined. No amendment or repeal of this paragraph 9
shall apply to or have any effect on the liability or alleged liability
<Page>

of any director of the corporation for or with respect to any acts or omissions
of such director occurring prior to such amendment or repeal.

      10. This corporation shall, to the maximum extent permitted from time to
time under the law of the State of Delaware, indemnify and upon request advance
expenses to any person who is or was a party or is threatened to be made a party
to any threatened, pending or completed action, suit, proceeding or claim,
whether civil, criminal, administrative or investigative, by reason of the fact
that such person is or was or has agreed to be a director or officer of this
corporation or while a director or officer is or was serving at the request of
this corporation as a director, officer, partner, trustee, employee or agent of
any corporation, partnership, joint venture, trust or other enterprise,
including service with respect to employee benefit plans, against expenses
(including attorney's fees and expenses), judgments, fines, penalties and
amounts paid in settlement incurred (and not otherwise recovered) in connection
with the investigation, preparation to defend or defense of such action, suit,
proceeding or claim; PROVIDED, HOWEVER, that the foregoing shall not require
this corporation to indemnify or advance expenses to any person in connection
with any action, suit, proceeding, claim or counterclaim initiated by or on
behalf of such person. Such indemnification shall not be exclusive of other
indemnification rights arising under any by-law, agreement, vote of directors or
stockholders or otherwise and shall inure to the benefit of the heirs and legal
representatives of such person. Any person seeking indemnification under this
paragraph 10 shall be deemed to have met the standard of conduct required for
such indemnification unless the contrary shall be established. Any repeal or
modification of the foregoing provisions of this paragraph 10 shall not
adversely affect any right or protection of a director or officer of this
corporation with respect to any acts or omissions of such director or officer
occurring prior to such repeal or modification.

      11. The books of this corporation may (subject to any statutory
requirements) be kept outside the State of Delaware as may be designated by the
board of directors or in the by-laws of this corporation.

      12. If at any time this corporation shall have a class of stock registered
pursuant to the provisions of the Securities Exchange Act of 1934, for so long
as such class is so registered, any action by the stockholders of such class
must be taken at an annual or special meeting of stockholders and may not be
taken by written consent.


                                       -2-
<Page>

      THE UNDERSIGNED, the sole incorporator named above, hereby certifies that
the facts stated above are true as of this 23rd day of July, 1996.


                                          /s/ Patrick O'Brien
                                          --------------------------------------
                                          Patrick O'Brien
                                          Sole Incorporator


                                      -1-
<Page>

                                                           STATE OF DELAWARE
                                                          SECRETARY OF STATE
                                                       DIVISION OF CORPORATIONS
                                                       FILED 09:00 AM 07/09/1999
                                                          991280618 - 2645754

                             CERTIFICATE OF REVIVAL
                                       OF
                          CERTIFICATE OF INCORPORATION
                                       OF
                            CHARLES RIVER BRF, INC.

            Under Section 312 of the Delaware General Corporation Law

      1. The name of the Corporation is Charles River BRF, Inc.

      2. The address of the Corporation's registered office in the State of
Delaware is: Corporation Service Company, 1013 Centre Road, Wilmington,
Delaware 19805. County of New Castle.

      3. The date of filing of the original certificate of incorporation was
July 25, 1996.

      4. The date when restoration, renewal, and revival of the charter of this
Corporation is to commence is the 28th day of February, 1999, same being prior
to the date of the expiration of the charter. This renewal and revival of the
charter of this Corporation is to be perpetual.

      5. Charles River BRF, Inc., desiring to be revived, was incorporated under
the laws of the State of Delaware.

      6. The certificate of incorporation was voided on March 1, 1999 for
failure to pay taxes in the State of Delaware.

      7. This Certificate of Revival was authorized by the directors of the
Corporation who were in office at the time the Certificate of Incorporation was
voided and who are now the directors of the Corporation.

      IN WITNESS WHEREOF, I the undersigned do make, file and record this
Certificate of Revival and do certify that the facts herein stated are true and
I have accordingly hereunto set my hand this 9th day of July, 1999.


                                      By: /s/ Alan H. Resnick
                                          -------------------
                                      Alan H. Resnick, Treasurer
<Page>

                                                           STATE OF DELAWARE
                                                          SECRETARY OF STATE
                                                       DIVISION OF CORPORATIONS
                                                       FILED 09:00 AM 07/09/1999
                                                          991280620 - 2645754

                            CERTIFICATE OF AMENDMENT

                                       OF

                          CERTIFICATE OF INCORPORATION

                                       OF

                            CHARLES RIVER BRF, INC.

                     (Pursuant to Section 242 of the General
                    Corporation Law of the State of Delaware)

      Charles River BRF, Inc., a corporation organized and existing under the
General Corporation Law of the State of Delaware (the "Corporation"), does
hereby certify that:

      1. The name of the Corporation is Charles River BRF, Inc.

      2. The name of the Corporation is hereby changed to "CRL Holdings, Inc."

      3. Each of the 100 issued and outstanding shares of the Corporation's
Common Stock, par value $.01 per share, are hereby changed into 300 shares of
Common Stock, par value $.01 per share, so that immediately after effecting such
change, the Corporation shall have a total of 30,000 shares of Common Stock, par
value $.01 per share, issued and outstanding.

      4. Article 4 of the Certificate of Incorporation of the Corporation is
hereby amended to read in its entirety as follows:

      "4. The Corporation is authorized to issue two (2) classes of shares to be
designated, respectively, Common Stock ("Common Stock") and Preferred Stock
("Preferred Stock"). The total number of shares of stock that the Corporation
shall be authorized to issue is Five Hundred Thousand (500,000). The total
number of shares of Common Stock that the Corporation shall be authorized to
issue is Two Hundred Fifty Thousand (250,000) shares of Common Stock with a par
value of $.01 per share. The total number of shares of Preferred Stock that the
Corporation shall be authorized to issue is Two Hundred Fifty Thousand (250,000)
shares of Series A Redeemable Preferred Stock with a par value of $.01 per
share.

      The rights, preferences and limitations granted to and imposed on the
authorized stock are as set forth below in this Article 4:
<Page>

                                      -2-


      A. COMMON STOCK. The Common Stock shall have the rights, preferences and
limitations granted to and imposed upon the Common Stock as are set forth in the
fo1lowing sections.

      SECTION 1. DIVIDEND RIGHTS. After payment in full of any dividends then
accrued with respect to the Preferred Stock, dividends payable in cash, stock or
otherwise, as may be declared by the Board of Directors, may be declared and
paid on the Common Stock from time to time out of any funds lawfully available
therefor.

      SECTION 2. VOTING RIGHTS. The holders of the Common Stock shall be
entitled to one (1) vote per share.

      SECTION 3. LIQUIDATION, DISSOLUTION OR WINDING UP. In the event of any
liquidation, dissolution or winding up of the Corporation, whether voluntary or
involuntary and after payment in full of the amount payable in respect of the
Preferred Stock, as provided in Paragraph B, Section 1(b) below, the holders of
the shares of Common Stock shall share ratably in the distribution of the
Residual Assets as defined in Paragraph B, Section 1(b) below.

      B. PREFERRED STOCK. The Preferred Stock shall consist of Two Hundred Fifty
Thousand (250,000) shares having a par value of $.O1 per share and shall be
designated as "Series A Redeemable Preferred Stock" (the "Series A Preferred
Stock"). The rights, preferences and limitations granted to and imposed on the
Preferred Stock are as set forth in the following sections:

      SECTION 1. RIGHTS, PREFERENCES AND LIMITATIONS OF SERIES A PREFERRED
STOCK.

      (a) DIVIDENDS. The holders of the Series A Preferred Stock, in preference
to the holders of all Common Stock, shall be entitled to receive when, as and if
declared by the Board of Directors out of funds legally available for the
purpose, cumulative dividends as provided in this Paragraph. Dividends on each
share of Series A Preferred Stock shall be payable in cash, and shall accrue at
the Dividend Rate on the sum of (i) the Purchase Price and (ii) all accumulated
and unpaid dividends accrued thereon pursuant to this Paragraph from the date of
issuance thereof (the "Series A Dividends"); the sum of the Purchase Price and
the Series A Dividends is referred to herein as the "Series A Preference
Amount." Such dividends will be calculated and compounded annually in arrears on
December 31 of each year (each a "Dividend Date") in respect of the prior twelve
month period, prorated on a daily basis for partial periods. Such dividends
shall commence to accrue on each share of Series A Preferred Stock from the date
of issuance thereof whether or not declared by the Board of Directors, and
whether or not there are profits, surplus or other funds of the Corporation
legally available for the payment of dividends, and shall continue to accrue
thereon until the Series A Preference Amount is paid in full in cash.

      (b) LIQUIDATION, DISSOLUTION OR WINDING UP. In the event of any
liquidation, dissolution or winding up of the Corporation, whether voluntary or
involuntary, subject to the rights of holders of other series of preferred stock
of the Corporation, each holder of outstanding shares of Series A Preferred
Stock and Common Stock shall be entitled to be paid out of the assets of the
Corporation available for distribution to stockholders, whether such assets are
<Page>

                                      -3-


capital, surplus, or earnings as follows: (i) first, the holders of the
outstanding shares of Series A Preferred Stock shall receive an amount in cash
equal to the Purchase Price together with any accrued but unpaid dividends to
which the holders of outstanding shares of such series are entitled pursuant to
Section 1(a) hereof (the "Series A Liquidation Preference") before any payment
shall be made to the holders of any Common Stock or of any other series of
preferred stock of the Corporation; and (ii) second, the holders of the
outstanding shares of Common Stock shall share ratably in the distribution of
the assets of the Corporation remaining for distribution to stockholders,
whether such assets are capital, surplus, or earnings (the "Residual Assets").

      (c) VOTING RIGHTS. The holders of Series A Preferred Stock shall not be
entitled to vote except as required by law.

      (d) CONVERSION. The Series A Preferred Stock shall not be convertible into
Common Stock or any other security of the Corporation.

      (e) REDEMPTION RIGHTS.

            (i) REDEMPTION RIGHTS OF THE HOLDER. At any time or from time to
time after the issuance of any shares of Series A Preferred Stock and prior to
the completion of a Public Offering, any holder of such shares shall have the
right to cause the Corporation to redeem its shares by notifying the Corporation
in writing of its intent to exercise the rights afforded by this Paragraph and
specifying a date not less than two (2) days (or such shorter period as may be
determined by mutual agreement of the holder and the Corporation) nor more than
thirty (30) days from the date of such notice on which the shares designated
therein shall be redeemed (the "Optional Redemption Date"). The Corporation
shall redeem on the Optional Redemption Date all shares of Series A Preferred
Stock which have been tendered for redemption in accordance with the foregoing,
together with stock powers duly endorsed for transfer to the Corporation.

            (ii) REDEMPTION RIGHTS OF THE CORPORATION. Subject to compliance
with applicable law, at any time or from time to time the Corporation shall have
the right to redeem any or all of the then outstanding shares of Series A
Preferred Stock. The Corporation shall notify the holders of Series A Preferred
Stock of its intent to exercise the rights afforded by this Paragraph and
specify a date not less than two (2) days (or such shorter period as may be
determined by mutual agreement of the holder and the Corporation) nor more than
thirty (30) days from the date of such notice on which the shares designated
therein shall be redeemed (the "Mandatory Redemption Date"). The recipient of
such notice shall tender to the Corporation the shares of Series A Preferred
Stock specified therein on or before such date, together with stock powers duly
endorsed for transfer to the Corporation.

            (iii) PAYMENT OF REDEMPTION PRICE. The total amount payable to a
holder of Series A Preferred Stock upon redemption of the shares hereunder shall
be the Series A Preference Amount of such shares (the "Redemption Price"). The
Redemption Price shall be paid in cash by wire transfer of immediately available
funds on the Optional Redemption Date or the Mandatory Redemption Date, as
applicable.

            (iv) STATUTORY LIMITATIONS. If the Corporation does not have
sufficient funds legally available to redeem all shares for which redemption is
requested hereunder, then it shall
<Page>

                                       -4-


redeem such shares on a pro rata basis among the holders of the Series A
Preferred Stock which requested redemption in proportion to the shares of Series
A Preferred Stock then held by them to the extent possible and shall redeem the
remaining shares to be redeemed as soon as sufficient funds are legally
available therefor.

      (f) NO REISSUANCE OF PREFERRED STOCK. No share or shares of Preferred
Stock acquired by the Corporation by reason of redemption, purchase, conversion
or otherwise shall be reissued, and all such shares shall be cancelled. The
Corporation may from time to time take such appropriate corporate action as may
be necessary to reduce the authorized number of shares of Preferred Stock
accordingly.

      (g) DEFINITIONS.

      "Certificate of Incorporation" shall mean the Certificate of Incorporation
of the Corporation, as amended from time to time.

      "Common Stock" shall mean the Corporation's Common Stock, $.01 par value
per share.

      "Dividend Date" shall have the meaning set forth in Paragraph B(1)(a)
hereof.

      "Dividend Rate" shall mean 7.5% per annum.

      "Person" shall mean an individual, partnership, corporation, association,
trust, joint venture, unincorporated organization and any government,
governmental department or agency or political subdivision thereof.

      "Public Offering" shall mean any underwritten offering by the Corporation
of its equity securities to the public pursuant to an effective registration
statement under the Securities Act of 1933 or any comparable statement under any
similar federal statute then in force, other than an offering of shares being
issued as consideration in a business acquisition or combination or an offering
in connection with an employee benefit plan.

      "Purchase Price" of any share of Series A Preferred Stock shall be $1,000.

      "Series A Preference Amount" shall have the meaning set forth in Paragraph
B(1)(a).

      "Series A Preferred Stock" shall mean the Corporation's Series A
Redeemable Preferred Stock, $.01 par value.

      5. The Board of Directors of the Corporation, by unanimous written consent
in lieu of a meeting pursuant to Section 141(f) of the General Corporation Law
of the State of Delaware, duly adopted resolutions declaring advisable this
Certificate of Amendment.
<Page>

                                      -5-


      6. In lieu of a meeting and vote of stockholders, the stockholders have
approved this Certificate of Amendment by written consent in accordance with the
provisions of Section 228 of the General Corporation Law of the State of
Delaware and the By-laws of the Corporation, and notice of the taking of such
action was duly given to stockholders not consenting in writing to such action.

      7. This Certificate of Amendment was duly adopted in accordance with
Sections 242 of the General Corporation Law of the State of Delaware.

      IN WITNESS WHEREOF, CHARLES RIVER BRF, Inc. has caused this Certificate of
Amendment to be signed by Alan H. Resnick, its Treasurer, this 9th day of July,
1999.

                                      CHARLES RIVER BRF, INC.


                                      By: /s/ Alan H. Resnick
                                      Alan H. Resnick, Treasurer
<Page>

                                                           STATE OF DELAWARE
                                                          SECRETARY OF STATE
                                                       DIVISION OF CORPORATIONS
                                                       FILED 09:00 AM 08/31/1999
                                                          991364079 - 2645754

                            CERTIFICATE OF AMENDMENT
                                       TO
                          CERTIFICATE OF INCORPORATION
                                       OF
                               CRL HOLDINGS, INC.

      CRL Holdings, Inc. (the "Corporation"), a corporation organized and
existing under and by virtue of the General Corporation Law of the State of
Delaware,

      DOES HEREBY CERTIFY:

      FIRST: That the Board of Directors of the Corporation, by the unanimous
written consent of its members, filed with the minutes of the Board, adopted a
resolution proposing and declaring advisable the following amendment to the
Certificate of Incorporation of the Corporation:

            RESOLVED: That the Certificate of Incorporation of Charles River
      Laboratories, Inc. be amended by changing Article 1 thereof so that, as
      amended, said Article shall be and read as follows:

            1. The name of the Corporation is Charles River Laboratories, Inc.

      SECOND: That in lieu of a meeting and vote of the stockholders, the
stockholders have given written consent to said amendment in accordance with the
provisions of Sections 228 and 242 of the General Corporation Law of the State
of Delaware.

      IN WITNESS WHEREOF, CRL Holdings, Inc. has caused this certificate to be
signed by Alan H. Resnick, its Treasurer, this 31st day of August, 1999.

                                      CRL Holdings, Inc.


                                      By: /s/ Alan H. Resnick
                                          -------------------
                                            Alan H. Resnick
                                            Treasurer
<Page>

                                                           STATE OF DELAWARE
                                                          SECRETARY OF STATE
                                                       DIVISION OF CORPORATIONS
                                                       FILED 09:00 AM 09/13/1999
                                                          991380860 - 2645754

                             CERTIFICATE OF MERGER

                                       OF

                              THERION CORPORATION

                                 WITH AND INTO

                        CHARLES RIVER LABORATORIES, INC.

  (Under Section 252 of the General Corporation Law of the State of Delaware)

      The undersigned, for the purpose of merging a foreign corporation with and
into a domestic corporation under the General Corporation Law of the State of
Delaware, does hereby certify that:

      FIRST: The name and state of incorporation of each of the constituent
corporations of the merger is as follows:

      (a) Therion Corporation, a New York corporation; and

      (b) Charles River Laboratories, Inc., a Delaware corporation.

      SECOND: An Agreement and Plan of Merger has been approved, adopted,
certified, executed and acknowledged by each of the constituent corporations in
accordance with the requirements of Section 252 of the General Corporation Law
of the State of Delaware.

      THIRD: The name of the surviving corporation is Charles River
Laboratories, Inc.

      FOURTH: The Certificate of Incorporation of Charles River Laboratories,
Inc. shall be the Certificate of Incorporation of the surviving corporation,
with no amendments or changes.

      FIFTH: The executed Agreement and Plan of Merger is on file at the
principal place of business of the surviving corporation, the address of which
is 1013 Centre Road, City of Wilmington, County of Delaware.

      SIXTH: A copy of the executed Agreement and Plan of Merger will be
furnished by the surviving corporation, on request and without cost, to any
stockholder of either of the constituent corporations.

      SEVENTH: The terminating corporation has authority to issue a single class
of common stock composed of 2,000 shares of common stock, no par value per
share.


<Page>

      IN WITNESS WHEREOF, Charles River Laboratories, Inc. has caused this
Certificate to be signed by its Vice President this 10th day of September, 1999.

                                         CHARLES RIVER LABORATORIES, INC.


                                         By:  /s/ Robert B. Stiles
                                            ------------------------------------
                                         Name:  Robert B. Stiles
                                         Title:  Vice President
<Page>

                                                          STATE OF DELAWARE
                                                          SECRETARY OF STATE
                                                       DIVISION OF CORPORATIONS
                                                       FILED 09:01 AM 09/13/1999
                                                          991380864 - 2645754

                              CERTIFICATE OF MERGER

                                       OF

                                 TEKTAGEN, INC.

                                      INTO

                        CHARLES RIVER LABORATORIES, INC.

   (Under Section 251 of the General Corporation Law of the State of Delaware)

      Charles River Laboratories, Inc., a Delaware corporation, does hereby
certify:

      FIRST: The name and state of incorporation of each of the constituent
corporations of the merger is as follows:

      (a) Tektagen, Inc., a Delaware corporation; and

      (b) Charles River Laboratories, Inc., a Delaware Corporation.

      SECOND: An Agreement and Plan of Merger has been approved, adopted,
certified, executed and acknowledged by Tektagen, Inc. and Charles River
Laboratories, Inc. in accordance with the provisions of subsection (c) of
Section 251 of the General Corporation Law of the State of Delaware.

      THIRD: The name of the surviving corporation is Charles River
Laboratories, Inc.

      FOURTH: That the Certificate of Incorporation of Charles River
Laboratories, Inc. a Delaware corporation, which is the surviving corporation,
shall continue without amendments or changes.

      FIFTH: The surviving corporation is a corporation of the State of
Delaware.

      SIXTH: The executed Agreement and Plan of Merger is on file at the
principal place of business of Charles River Laboratories, Inc. at 1013 Centre
Road, City of Wilmington, County of Delaware.

      SEVENTH: A copy of the Agreement and Plan of Merger will be furnished by
Charles River Laboratories, Inc., on request and without cost, to any
stockholder of any constituent corporation.

      EIGHTH: Tektagen, Inc. has authority to issue a single class of stock
composed of 3,000 common shares, $.01 par value per share.

<Page>

                                      -2-


      IN WITNESS WHEREOF, Charles River Laboratories, Inc. has caused this
Certificate to be signed by its Vice President this 10th day of September, 1999.

                                         CHARLES RIVER LABORATORIES, INC.


                                         By:  /s/ Robert B. Stiles
                                            ------------------------------------
                                         Name:  Robert B. Stiles
                                         Title:  Vice President
<Page>

                              CERTIFICATE OF MERGER

                                       OF

                        CHARLES RIVER PHARMSERVICES, INC.

                                  WITH AND INTO

                        CHARLES RIVER LABORATORIES, INC.

   (Under Section 252 of the General Corporation Law of the State of Delaware)

      The undersigned, for the purpose of merging a foreign corporation with and
into a domestic corporation under the General Corporation Law of the State of
Delaware, does hereby certify that:

      FIRST: The name and state of incorporation of each of the constituent
corporations of the merger is as follows:

      (a) Charles River PharmServices, Inc., a Massachusetts corporation; and

      (b) Charles River Laboratories, Inc., a Delaware corporation.

      SECOND: An Agreement and Plan of Merger has been approved, adopted,
certified, executed and acknowledged by each of the constituent corporations in
accordance with the requirements of Section 252 of the General Corporation Law
of the State of Delaware.

      THIRD: The name of the surviving corporation is Charles River
Laboratories, Inc.

      FOURTH: The Certificate of Incorporation of Charles River Laboratories,
Inc. shall be the Certificate of Incorporation of the surviving corporation,
with no amendments or changes.

      FIFTH: The executed Agreement and Plan of Merger is on file at the
principal place of business of the surviving corporation, the address of which
is 1013 Centre Road, City of Wilmington, County of Delaware.

      SIXTH: A copy of the executed Agreement and Plan of Merger will be
furnished by the surviving corporation, on request and without cost, to any
stockholder of either of the constituent corporations.

      SEVENTH: Charles River Pharmservices, Inc. had authority to issue a single
class of common stock composed of 200,000 shares of common stock, no par value.

                                                          STATE OF DELAWARE
                                                          SECRETARY OF STATE
                                                       DIVISION OF CORPORATIONS
                                                       FILED 09:02 AM 09/13/1999
                                                          991385037 - 2645754

<Page>

                                       -2-


      IN WITNESS WHEREOF, Charles River Laboratories, Inc. has caused this
Certificate to be signed by its Vice President this 10th day of September, 1999.

DATED: September 10, 1999

                                         CHARLES RIVER LABORATORIES, INC.


                                         By:  /s/ Robert B. Stiles
                                            ------------------------------------
                                         Name:  Robert B. Stiles
                                         Title:  Vice President
<Page>

                                                          STATE OF DELAWARE
                                                          SECRETARY OF STATE
                                                       DIVISION OF CORPORATIONS
                                                       FILED 09:00 AM 09/13/1999
                                                          991390241 - 2645754

                            CERTIFICATE OF CORRECTION
                                     OF THE
                            CERTIFICATE OF AMENDMENT
                                       OF
                        Charles River Laboratories, Inc.

      The undersigned, being the Vice President of Charles River Laboratories,
Inc. (the "Corporation"), for the purpose of correcting a Certificate of
Amendment of the Corporation's Certificate of Incorporation under Section 103(f)
of the General Corporation Law of the State of Delaware, does hereby certify:

      1. The name of the Corporation is Charles River Laboratories, Inc.

      2. The Corporation's original Certificate of Incorporation was filed
with the Secretary of State on July 25, 1996.

      3. The Corporation's Certificate of incorporation was amended by a
Certificate of Amendment filed with the Secretary of State on August 31, 1999.

      4. The Certificate of Amendment of the Corporation's Certificate of
Incorporation filed with the Secretary of State on August 31, 1999 was an
inaccurate record of the corporate action therein referred to in that in
Paragraph First, the RESOLVED paragraph recited the name of the Corporation as
"Charles River Laboratories, Inc." instead of CRL Holdings, Inc., which was the
name of the Corporation at the time the Certificate of Amendment was presented
for filing.

      5. The true and correct amended Paragraph First of the Certificate of
Amendment of the Certificate of Incorporation, which is an accurate record of
the corporate action therein referred to, is as follows:

"FIRST: That the Board of Directors of the Corporation, by unanimous written
consent of its members, filed with the minutes of the Board, adopted a
resolution proposing and declaring advisable the following amendment to the
Certificate of Incorporation of the Corporation:

      RESOLVED: That the Certificate of Incorporation of CRL Holdings, Inc. be
      amended by changing Article 1 thereof so that, as amended, said Article
      shall be and read as follows:

      1. The name of the Corporation is Charles River Laboratories, Inc.
<Page>

                                       -2-


      I, THE UNDERSIGNED, being the Vice President of the Corporation, for the
purpose of correcting the Corporation's Certificate of Incorporation under the
laws of the State of Delaware, do make, file and record this Certificate of
Correction of the Certificate of Amendment of the Certificate of Incorporation,
do certify that the facts herein stated are true, and accordingly, have hereunto
set my hand as of the 17th day of September, 1999.


                                             By: /s/ Robert B. Stiles
                                                ------------------------------
                                                  Robert B. Stiles
                                                  Vice President
<Page>

                                                            STATE OF DELAWARE
                                                           SECRETARY OF STATE
                                                        DIVISION OF CORPORATIONS
                                                       FILED 09:00 AM 10/29/1999
                                                          991461071 - 2645754

                       CERTIFICATE OF OWNERSHIP AND MERGER

                                     MERGING

                               SBI HOLDINGS, INC.
                              a Nevada Corporation

                                      INTO

                        CHARLES RIVER LABORATORIES, INC.
                             a Delaware Corporation

                     (PURSUANT TO SECTION 253 OF THE GENERAL
                          CORPORATION LAW OF DELAWARE)

      Charles River Laboratories, Inc., a Delaware corporation (the
"Corporation"), does hereby certify:

      FIRST: That the Corporation is incorporated pursuant to the General
Corporation Law of the State of Delaware.

      SECOND: That the Corporation owns all of the outstanding shares of each
class of the capital stock of SBI Holdings, Inc., a Nevada Corporation.

      THIRD: That the Corporation, by the following resolution of its Board of
Directors, duly adopted on the 28th day of October, 1999, determined to merge
into itself SBI Holdings, Inc. on the conditions set forth in such resolution:

      RESOLVED: That, pursuant to Section 253 of the General Corporation Law
                of the State of Delaware and the applicable laws of the
                State of Nevada, SBI Holdings, Inc., a Nevada corporation,
                its wholly owned subsidiary (the "Subsidiary"), merge with
                and into this Corporation (the "Merger"); that the effective
                time of the Merger (the "Effective Time") shall be at such
                time as the Certificate of Ownership and Merger of the
                Subsidiary with and into this Corporation is filed with the
                office of the Secretary of State of the State of Delaware
                and the corresponding Articles of Merger are filed with the
                Secretary of State of the State of Nevada; that it is in the
                best interest of this Corporation and the Subsidiary that
                the corporations merge, with this Corporation being the
                surviving corporation (the "Surviving Corporation"); that at
                the Effective Time, (i) the Surviving Corporation shall
                assume all of the Subsidiary's liabilities and obligations
                pursuant to the Nevada Revised Statutes and Section 253 of


                                       -1-
<Page>

                the General Corporation Law of the State of Delaware, (ii)
                the identity, existence, rights, privileges, powers,
                franchises, properties and assets of the Surviving
                Corporation shall continue unaffected and unimpaired by the
                Merger, and (iii) the identity and separate existence of the
                Subsidiary shall cease and all of the rights, privileges,
                powers, franchises, properties and assets of the Subsidiary
                shall be vested in the Surviving Corporation; and that the
                President, any Vice President, and the Secretary and any
                Assistant Secretary of this Corporation at the time in
                office be, and they are, and each of them acting singly is,
                hereby authorized, in the name and on behalf of this
                Corporation, to take any and all actions to execute, file or
                cause to be filed any and all documents, agreements,
                instruments or certificates, including without limitation
                executing and filing a Certificate of Ownership and Merger
                pursuant to Sections 103 and 253 of the General Corporation
                Law of Delaware, and to do or cause to be done any and all
                other things as such officer or officers may in his, her or
                their judgment deem necessary, desirable or appropriate in
                order to give effect to, and carry out the intent of, this
                resolution, the execution and delivery of any such
                documents, instruments or certificates and the taking of any
                such action to be conclusive evidence that the same has been
                approved by this Board of Directors.

      FOURTH: That this Certificate shall be effective upon the filing of this
Certificate with the Secretary of State of the State of Delaware.


                                      -2-
<Page>

           IN WITNESS WHEREOF, said corporation has caused this certificate to
be signed by its authorized officer, the 28th day of October, 1999.

                                         CHARLES RIVER LABORATORIES, INC.


                                         BY:  /s/ Dennis Shaughnessy
                                            ------------------------------------
                                         NAME:  Dennis Shaughnessy
                                         TITLE:  Vice President

Attest:


/s/ [ILLEGIBLE]
-----------------------------------
Asst. Secretary


                                      -3-
<Page>

                                                          STATE OF DELAWARE
                                                          SECRETARY OF STATE
                                                       DIVISION OF CORPORATIONS
                                                       FILED 03:00 PM 03/30/2001
                                                          010159603 - 2645754

                       CERTIFICATE OF OWNERSHIP AND MERGER

                                       OF

                              PRIMEDICA CORPORATION

                                      INTO

                        CHARLES RIVER LABORATORIES, INC.

      Charles River Laboratories, Inc., a corporation organized and existing
under the laws of the State of Delaware (hereinafter sometimes referred to as
the "Corporation"), does hereby certify:

      FIRST: That the Corporation is a business corporation organized under the
laws of the State of Delaware.

      SECOND: That the Corporation is the owner of all of the outstanding shares
(of each class) of stock of Primedica Corporation, which is also a business
corporation organized under the laws of the State of Delaware.

      THIRD: On March 27, 2001, the Executive Committee of the Board of
Directors of the Corporation adopted the following resolutions by written
consent to merge Primedica Corporation into the Corporation:

      RESOLVED: That Primedica Corporation be merged into this Corporation,
                and that all of the estate, property, rights, privileges,
                powers and franchises of Primedica Corporation be vested in
                and held and enjoyed by the Corporation as fully and
                entirely and without change or diminution as the same were
                before held and enjoyed by Primedica Corporation in its
                name; and

      FURTHER
      RESOLVED: That this Corporation shall assume all of the obligations of
                Primedica Corporation; and

      FURTHER
      RESOLVED: That this Corporation shall cause to be executed and filed
                and/or recorded the documents prescribed by the laws of the
                State of Delaware and by the laws of any other appropriate
                jurisdiction and will cause to be performed all necessary
                acts within the State of Delaware and within any other
                appropriate jurisdiction; and
<Page>

      FURTHER
      RESOLVED: That the effective time of the Certificate of Ownership and
                Merger setting forth a copy of these resolutions, and the
                time when the merger therein provided for, shall become
                effective shall be upon filing with the Delaware Secretary
                of State.

      IN WITNESS WHEREOF, said Charles River Laboratories, Inc. has caused this
Certificate to be signed by Dennis R. Shaughnessy, its Senior Vice President,
Business Development, this 27th day of March, 2001.

                                CHARLES RIVER LABORATORIES, INC.


                                /s/ Dennis R. Shaughnessy
                                ---------------------------------------------
                                By:  Dennis R. Shaughnessy
                                Its: Senior Vice President, Business Development
<Page>

                                                          STATE OF DELAWARE
                                                          SECRETARY OF STATE
                                                       DIVISION OF CORPORATIONS
                                                       FILED 09:00 AM 04/10/2001
                                                          010174830 - 2645754

                       CERTIFICATE OF OWNERSHIP AND MERGER

                                       OF

                 PATHOLOGY ASSOCIATES INTERNATIONAL CORPORATION

                                      INTO

                        CHARLES RIVER LABORATORIES, INC.

      Charles River Laboratories, Inc., a corporation organized and existing
under the laws of the State of Delaware (hereinafter sometimes referred to as
the "Corporation"), does hereby certify:

      FIRST: That the Corporation is a business corporation organized under the
laws of the State of Delaware.

      SECOND: That the Corporation is the owner of all of the outstanding shares
(of each class) of stock of Pathology Associates International Corporation,
which is also a business corporation organized under the laws of the State of
Delaware.

      THIRD: On April 6, 2001, the Executive Committee of the Board of Directors
of the Corporation adopted the following resolutions by written consent to merge
Pathology Associates International Corporation into the Corporation:

      RESOLVED: That Pathology Associates International Corporation, a
                Delaware corporation ("PAIC") be merged into this
                Corporation, and that all of the estate, property, rights,
                privileges, powers and franchises of PAIC be vested in and
                held and enjoyed by the Corporation as fully and entirely
                and without change or diminution as the same were before
                held and enjoyed by PAIC in its name; and

      FURTHER
      RESOLVED: That this Corporation shall assume all of the obligations of
                PAIC; and

      FURTHER
      RESOLVED: That this Corporation shall cause to be executed and filed
                and/or recorded the documents prescribed by the laws of the
                State of Delaware and by the laws of any other appropriate
                jurisdiction and will cause to be performed all necessary
                acts within the State of Delaware and within any other
                appropriate jurisdiction; and
<Page>

      FURTHER
      RESOLVED: That the effective time of the Certificate of Ownership and
                Merger setting forth a copy of these resolutions, and the
                time when the merger therein provided for shall become
                effective, shall be upon filing with the Delaware Secretary
                of State.

      IN WITNESS WHEREOF, said Charles River Laboratories, Inc. has caused this
Certificate to be signed by Dennis R. Shaughnessy, its Senior Vice President,
Business Development, this 6th day of April, 2001.

                                CHARLES RIVER LABORATORIES, INC.


                                /s/ Dennis R. Shaughnessy
                                ---------------------------------------------
                                By:  Dennis R. Shaughnessy
                                Its: Senior Vice President, Business Development
<Page>

   STATE OF DELAWARE
   SECRETARY OF STATE
DIVISION OF CORPORATIONS
FILED 04:00 PM 07/25/2001
   010361196 - 2645754

                       CERTIFICATE OF OWNERSHIP AND MERGER

                                       OF

                              GENETIC MODELS, INC.

                                      INTO

                        CHARLES RIVER LABORATORIES, INC.

      Charles River Laboratories, Inc., a corporation organized and existing
under the laws of the State of Delaware (hereinafter sometimes referred to as
the "Corporation"), does hereby certify:

      FIRST: That the Corporation is a business corporation organized under the
laws of the State of Delaware.

      SECOND: That the Corporation is the owner of all of the outstanding shares
(of each class) of stock of Genetic Models, Inc., which is a business
corporation organized under the laws of the State of Indiana.

      THIRD: On July 17th 2OO1, the Executive Committee of the Board of
Directors of the Corporation adopted the following resolutions by written
consent to merge Genetic Models, Inc. into the Corporation:

      RESOLVED: That Genetic Models, Inc., an Indiana corporation ("GMI") be
                merged into this Corporation, and that all of the estate,
                property, rights, privileges, powers and franchises of GMI
                be vested in and held and enjoyed by the Corporation as
                fully and entirely and without change or diminution as the
                same were before held and enjoyed by GMI in its name; and

      FURTHER
      RESOLVED: That this Corporation shall assume all of the obligations of
                GMI; and

      FURTHER
      RESOLVED: That this Corporation shall cause to be executed and filed
                and/or recorded the documents prescribed by the laws of the
                State of Delaware and by the laws of any other appropriate
                jurisdiction and will cause to be performed all necessary
                acts within the State of Delaware and within any other
                appropriate jurisdiction; and

<Page>

      FURTHER
      RESOLVED: That the effective time of the Certificate of Ownership and
                Merger setting forth a copy of these resolutions, and the
                time when the merger therein provided for shall become
                effective, shall be upon filing with the Delaware Secretary
                of State.

      IN WITNESS WHEREOF, said Charles River Laboratories, Inc. has caused this
Certificate to be signed by Dennis R. Shaughnessy, its Senior Vice President,
Corporate Development, this 20th day of July, 2001.

                               CHARLES RIVER LABORATORIES, INC.


                               /s/ Dennis R. Shaughnessy
                               ---------------------------------------------
                               By:  Dennis R. Shaughnessy
                               Its: Senior Vice President, Corporate Development