EXHIBIT 5.1


                                                                  (512) 305-4716


                               September 10, 2003


International Isotopes Inc.
4137 Commerce Circle
Idaho Falls, Idaho  83401

         Re:   Registration  of 20,000,000  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 20,000,000
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 2002 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  20,000,000  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.
September 10, 2003
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/bsh





                                        2