Exhibit 5.3





                                                               December 12, 2001


Unigene Laboratories, Inc.
110 Little Falls Road
Fairfield, New Jersey 07004

Gentlemen:

               This opinion is being furnished to you in connection with the
filing by Unigene Laboratories, Inc., a Delaware corporation (the "Company"), of
Post-Effective Amendment No. 2 on Form S-1 to a Registration Statement on Form
S-3, File No. 333-04557 (the "Registration Statement") with the Securities and
Exchange Commission under the Securities Act of 1933, as amended. The
Registration Statement, as so amended, provides for the registration for resale
by the selling stockholders identified therein of up to the number of shares of
the Company's common stock, par value $.01 per share (the "Common Stock"),
specified in the prospectus forming Part I of the Registration Statement (the
"Prospectus"). This opinion covers only those shares of Common Stock
specifically identified in this opinion. All other shares of Common Stock
covered by the Registration Statement and Prospectus are the subject of opinions
previously filed as exhibits to the Registration Statement.

               For purposes of this opinion, we have examined the Registration
Statement. We also have examined and relied upon a copy of the Company's
Certificate of Incorporation, certified by the Secretary of State of the State
of Delaware, and copies of the Company's By-Laws and certain resolutions adopted
by the Board of Directors of the Company, each certified by the Corporate
Secretary of the Company.

               We also have reviewed the following documents:

               (1) A letter, dated September 29, 2000, to Annette North, from
Warren P. Levy, President, Unigene Laboratories, Inc. and a letter, dated
December 5, 2000, to Annette North ("North"), from William Steinhauer,
Controller, Unigene Laboratories, Inc., pursuant to which the Company has agreed
to issue to North, in addition to 62,000 shares of Common Stock that were issued
to North in connection with the exercise of a Warrant (the "Warrant Shares"),
additional shares of Common Stock. The additional shares of Common Stock
issuable to North consist of (i) shares of Common Stock that the Company is
contractually obligated to issue to North based on the closing price of the
Common Stock on the date that a post-effective amendment to the Registration
Statement that registers such shares for resale is declared





effective (the "Effective Date"), which number of shares will be determined as
of the Effective Date (the "Settlement Shares"), and (ii) shares of Common Stock
that the Company is contractually obligated to issue to North if the market
price of the Common Stock decreases during the ten trading days following the
delivery to North after the Effective Date of certificates for the Warrant
Shares and the Settlement Shares, which number of shares, if any, will be
calculated immediately following the expiration of the ten-day period (the
"Additional Shares"). The Board of Directors of the Company has reserved for
issuance an aggregate of 538,000 shares of Common Stock to satisfy its
obligations with respect to the Settlement Shares and the Additional Shares
(collectively, the "North Shares").

               (2) (i) a Warrant, dated September 1, 1995, issued by the Company
to Patrick Tedesco ("Tedesco") entitling Tedesco to purchase 50,000 shares of
Common Stock (the "Warrant"), and (ii) a letter, dated July 25, 2001, to Tedesco
from Warren P. Levy, President, Unigene Laboratories, Inc., pursuant to which
the Company agreed to issue to Tedesco an aggregate of 300,000 shares of Common
Stock in consideration for the exercise of the Warrant (the "Tedesco Shares").

               (3) a confirmation set forth in a letter, dated December 22,
2000, to Synexus Ltd. ("Synexus"), from William Steinhauer, Controller, Unigene
Laboratories, Inc., pursuant to which the Company agreed to issue to Synexus
125,000 shares of Common Stock in consideration for a payment obligation of the
Company to Synexus for services rendered (the "Synexus Shares").

               We further have examined such other documents and made such other
investigations as we have deemed necessary to form a basis for the opinion
hereinafter expressed. In examining the foregoing documents, we have assumed the
authenticity of documents submitted to us as originals, the genuineness of all
signatures, the conformity to original documents of documents submitted to us as
copies, and the accuracy of the representations and statements included therein.

               Based on the foregoing, we are of the opinion that the North
Shares, the Tedesco Shares and the Synexus Shares have been duly authorized for
issuance, and, if and when issued and delivered by the Company to North, Tedesco
and Synexus, in accordance with the terms of the Company's respective
obligations to them, will be validly issued, fully paid, and nonassessable.

               We hereby consent to the filing of this opinion as an exhibit to
Post-Effective Amendment No. 2 to the Registration Statement and to the use of
our name in the Prospectus forming a part thereof under the heading "Legal
Matters."

                                                       Very truly yours,


                                                       /s/ Covington & Burling
                                                       -----------------------
                                                       COVINGTON & BURLING