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                                                                       Exhibit 5


[Morgan, Lewis & Bockius LLP Letterhead]


November 22, 2000


Cell Pathways, Inc.
702 Electronic Drive
Horsham, PA 19044

Re:      Cell Pathways, Inc.
         Registration Statement on Form S-3

Ladies and Gentlemen:

As counsel to Cell Pathways, Inc., a Delaware corporation (the "Company"), we
have assisted in the preparation of the subject Registration Statement on Form
S-3, as amended (the "Registration Statement"), to be filed with the Securities
and Exchange Commission under the Securities Act of 1933, as amended (the
"Act"), relating to the shelf registration of 7,703,249 shares of the Company's
common stock (the "Shares") sold in a private offering to the selling
stockholders.

In rendering the opinion set forth below, we have reviewed (a) the Registration
Statement; (b) the Certificate of Incorporation, as amended, and the Bylaws, as
amended, of the Company, as in effect on the date hereof; (c) certain records of
the Company's corporate proceedings as reflected in its minute books; and (d)
such records, documents, statutes and decisions as we have deemed relevant. In
our examination, we have assumed the genuineness of all signatures, the
authenticity of all documents submitted to us as originals and the conformity
with the original of all documents submitted to us as copies thereof. The
opinion set forth below is limited to the General Corporation Law of the State
of Delaware, as amended.

Based upon the foregoing, we are of the opinion that the Shares are validly
issued, fully paid and nonassessable.

We hereby consent to the use of this opinion as Exhibit 5 to the Registration
Statement and to the reference to our firm under the heading `Legal Matters' in
the Registration Statement. In giving such opinion, we do not thereby admit that
we are acting within the category of persons whose consent is required under
Section 7 of the Act or the rules or regulations of the Securities and Exchange
Commission thereunder.

Very truly yours.

/s/ Morgan, Lewis & Bockius LLP