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                                                                     EXHIBIT 5.1
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May 22, 1997


IDEXX Laboratories, Inc.
One IDEXX Drive
Westbrook, Maine  04092

     Re:  1997 Employee Stock Purchase Plan, 1997 International Employee
          Stock Purchase Plan and 1997 Director Option Plan
          -------------------------------------------------

Ladies and Gentlemen:

     I am General Counsel to IDEXX Laboratories, Inc., a Delaware corporation
(the "Company"). In such capacity, I have assisted in the preparation of a
Registration Statement on Form S-8 (the "Registration Statement") to be filed
with the Securities and Exchange Commission relating to the registration of
482,500 shares of Common Stock, par value $.10 per share (the "Shares"), of the
Company, issuable under the Company's 1997 Employee Stock Purchase Plan, the
Company's 1997 International Employee Stock Purchase Plan, and upon exercise of
options granted under the 1997 Director Option Plan (the "Plans").

     I have examined the Restated Certificate of Incorporation of the Company,
as amended, the Amended and Restated By-Laws of the Company, as amended, and
originals, or copies certified to my satisfaction, of all pertinent records of
the meetings of the directors and stockholders of the Company, the Registration
Statements and such other documents relating to the Company as I have deemed
material for purposes of this opinion.

     In my examination of the foregoing documents, I have assumed the
genuineness of all signatures and the authenticity of all documents submitted to
me as originals, the conformity to original documents of all documents submitted
to me as certified or photostatic copies, and the authenticity of the originals
of such latter documents.

     Based on the foregoing, I am of the opinion that the Company has duly
authorized for issuance the shares covered by the Registration Statements to be
issued under each of the Plans, as described in the Registration Statement, and
the shares, when issued in accordance with the terms of each of the Plans, will
be legally issued, fully paid and nonassessable.

     I hereby consent to the filing of this opinion with the Securities and
Exchange Commission in connection with the Registration Statements.

                                    Very truly yours,


                                    /s/ Richard B. Thorp
                                    --------------------------
                                    Richard B. Thorp
                                    General Counsel