EXHIBIT 5.1

               Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.

                              One Financial Center
                           Boston, Massachusetts 02111
                                                                617 542 6000
                                                                617 542 2241 FAX



                                          June 7, 2001

Vertex Pharmaceuticals Incorporated
130 Waverly Street
Cambridge, Massachusetts 02139

Ladies and Gentlemen:

         We have acted as counsel to Vertex Pharmaceuticals Incorporated, a
Massachusetts corporation (the "Company"), in connection with the Registration
Statement on Form S-4 (File No. 333-61480) (the "Registration Statement") filed
by the Company with the Securities and Exchange Commission (the "SEC") for the
purpose of registering with the SEC under the Securities Act of 1933, as amended
(the "Securities Act"), up to 14,725,000 shares of the Company's common stock,
$0.01 par value per share (the "Shares"), pursuant to the Agreement and Plan of
Merger, dated as of April 29, 2001, among the Company, Ahab Acquisition Sub,
Inc. and Aurora Biosciences Corporation (the "Merger Agreement").

         In connection with the rendering of the opinion set forth below, we
have examined, are familiar with and, to the extent we deemed appropriate, we
have relied on originals or copies, certified or otherwise, identified to our
satisfaction, of (i) the Registration Statement, (ii) the Restated Articles of
Organization, as amended, and the Amended and Restated By-laws of the Company
currently in effect, (iii) the Merger Agreement, (iv) the resolutions adopted by
the Board of Directors of the Company as of April 29, 2001, relating to the
Merger Agreement and certain related matters and (v) such other documents,
agreements, records, instruments, certificates of public officials and
certificates of officers or other representatives of the Company or others as we
have deemed necessary or appropriate for purposes of and as a basis for
rendering the opinion set forth below.

         In our examination, we have (i) assumed the genuineness of all
signatures and the authenticity of all documents submitted to us as originals,
(ii) assumed the conformity to original documents of all documents submitted to
us as certified or photostatic copies and the authenticity of the originals of
such copies and (iii) assumed and relied upon the truth, accuracy and
completeness (without independent investigation or verification) of the
information, representations, warranties and statements contained in the
records, documents, instruments and certificates we have reviewed. In rendering
the opinion set forth below, we have assumed that such parties had, have or will
have all requisite power and authority to execute and deliver all agreements,
documents, instruments and certificates examined by us and have also assumed the
due authorization by all requisite action, and the due execution and delivery by
such parties of all such agreements, documents, instruments and certificates and
the validity and binding effect thereof. As to any facts material to the opinion
expressed herein which we have not

                  BOSTON NEW YORK WASHINGTON RESTON NEW HAVEN




Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.

Vertex Pharmaceuticals Incorporated
June 7, 2001
Page 2


independently established or verified, we have relied upon statements and
representations of officers and other representatives of the Company and others.

         Our opinion is limited to the the laws of the Commonwealth of
Massachusetts (including the applicable provisions of the Massachusetts
Constitution and the reported judicial decisions interpreting the laws) and the
federal laws of the United States of America. We express no opinion with respect
to the laws of any other jurisdiction and no opinion is expressed herein with
respect to the qualification of the Shares under the securities or blue sky laws
of any state or any foreign jurisdiction.

         Based upon and subject to the foregoing, we are of the opinion that the
Shares have been duly authorized for issuance in connection with the Merger (as
defined in the Merger Agreement) and, upon consummation of the Merger, the
issuance of the Shares and the delivery of proper stock certificates therefor in
accordance with the terms and conditions of the Merger Agreement, the Shares
will be validly issued, fully paid and non-assessable.

         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the reference to this opinion under the caption
"Legal Matters" in the joint proxy statement-prospectus included therein. In
giving this consent, we do not thereby admit that we are included in the
category of persons whose consent is required under Section 7 of the Securities
Act or the rules and regulations of the SEC promulgated thereunder.

         This opinion is furnished by us, as counsel to the Company, in
accordance with the requirements of Item 601(b)(5) of Regulation S-K under the
Securities Act and, except as provided in the immediately preceding paragraph,
is not to be used, circulated or quoted for any other purpose or otherwise
referred to or relied upon by any other person without the express written
permission of the Company.

                                                Very truly yours,

                                                /s/ Mintz, Levin, Cohn, Ferris,
                                                    Glovsky and Popeo, P.C.

                                                    Mintz, Levin, Cohn, Ferris,
                                                    Glovsky and Popeo, P.C.