EXHIBIT 5.1

                                  Legal Opinion





                                                        (512) 305-4716


                                                        January 22, 1999

International Isotopes Inc.
3100 Jim Christal Road
Denton, TX 76207

         Re:      Registration of 600,000 shares of Common Stock pursuant to a
                  Registration Statement on Form S-8

Gentlemen:

        We have acted as counsel for International Isotopes Inc., a Texas
corporation (the "Company"), in connection with the registration under the
Securities Act of 1933, as amended (the "Securities Act"), pursuant to a
Registration Statement on Form S-8 (the "Registration Statement") of 600,000
shares of Common Stock, $.01 par value, of the Company ("Common Stock") to be
issued pursuant to the exercise of options (the "Options") granted or to be
granted by the Company to certain key employees, directors and consultants
pursuant to the Company's 1997 Long Term Incentive Plan (the "Plan").

        We have made such inquires and examined such documents as we have
considered necessary or appropriate for the purpose of giving the opinions
hereinafter set forth. We have assumed the genuineness and authenticity of all
signatures on all original documents, the authenticity of all documents
submitted to us as originals, the conformity to originals of all documents
submitted to us as copies and the due authorization, execution, delivery or
recordation of all documents where due authorization, execution or recordation
are prerequisites to the effectiveness thereof.

        Based upon the foregoing, having regard for such legal considerations as
we deem relevant, and assuming, with respect to the shares of Common Stock
issued under the Options (i) the receipt of proper consideration for the
issuance thereof in excess of the par value thereof, (ii) the availability of a
sufficient number of shares of Common Stock authorized by the Company's Articles
of Incorporation then in effect, (iii) compliance with the terms of the Plan,
and (iv) no change occurs in applicable law or the pertinent facts, we are of
the opinion that the 600,000 shares of Common Stock that may be issued and sold
by the Company from time to time upon exercise of the Options, as described in
the Registration Statement, will, upon issuance and delivery against payment
therefor, be duly authorized and legally issued, fully paid and nonassessable.





International Isotopes Inc.
January 22, 1999
Page 2

        We hereby consent to the filing of this opinion with the Securities and
Exchange Commission as an exhibit to the Registration Statement. By so
consenting, we do not thereby admit that our firm's consent is required by
Section 7 of the Securities Act.

                                            Very truly yours,

                                            LOCKE LIDDELL & SAPP LLP


                                            /s/ Locke Liddell & Sapp LLP

CRA/bsa