Exhibit 5
                                                                   ---------

                         NUTTER, McCLENNEN & FISH, LLP

                               ATTORNEYS AT LAW

                            ONE INTERNATIONAL PLACE
                       BOSTON, MASSACHUSETTS  02110-2699

           TELEPHONE: 617-439-2000          FACSIMILE: 617-973-9748

CAPE COD OFFICE                                             DIRECT DIAL NUMBER
HYANNIS, MASSACHUSETTS


                                 June 8, 2000


Nabi
5800 Park of Commerce Boulevard, N.W.
Boca Raton, FL  33487

Gentlemen/Ladies:

         Reference is made to the registration statement on Form S-8 (the
"Registration Statement") which Nabi (the "Company") is filing concurrently
herewith with the Securities and Exchange Commission under the Securities Act of
1933, as amended (the "Securities Act"), with respect to 2,196,922 shares of the
Company's common stock, $0.10 par value per share (the "Common Stock"),
consisting of 1,696,922 which are issuable pursuant to the Nabi 2000 Employee
Stock Plan (the "Equity Plan"), and 500,000 which are issuable pursuant to the
Nabi 2000 Employee Stock Purchase Plan (the "Stock Purchase Plan" and together
with the Equity Plan, the "Plans"), and an indeterminate number of shares of
such Common Stock which may be issued or become issuable under the Plans by
reason of stock dividends, stock splits or other recapitalizations executed
hereafter.

         We have acted as legal counsel for the Company in connection with the
creation of the Plans, are familiar with the Company's Amended and Restated
Certificate of Incorporation and By-laws, both as amended to date (collectively,
the "Organizational Documents"), and have examined such other documents as we
deemed necessary for this opinion. Based upon the foregoing, we are of the
opinion that:

         1.   When issued and paid for in compliance with the terms of the
applicable Plan, the Organizational Documents and the Delaware General
Corporation Law, the 2,196,922 shares of Common Stock referred to above will be
duly and validly issued, fully paid and non-assessable; and

         2.   The additional shares of Common Stock which may become issuable
under the Plans by reason of stock dividends, stock splits or other
recapitalizations hereafter executed, if and when issued in accordance with the
terms of the applicable Plan and upon compliance with the applicable provisions
of law and of the Organizational Documents, will be duly and validly issued,
fully paid and non-assessable.

     We understand that this opinion letter is to be used in connection with the
Registration Statement and hereby consent to the filing of this opinion letter
with and as a part of the Registration Statement and of any amendments thereto.
It is understood that this opinion letter is to be used in connection with the
offer and sale of the aforesaid shares only while the Registration Statement, as
it may be amended from time to time as contemplated by Section 10(a)(3) of the
Securities Act, is effective under the Securities Act.

                             Very truly yours,



                             Nutter, McClennen & Fish, LLP

NCH/CA