EXHIBIT 5.1



                                                                  (512) 305-4716


                                December 15, 2004

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

         Re:    Registration  of 2,000,000  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 2,000,000
shares of Common Stock,  $.01 par value, of the Company  ("Common  Stock") to be
issued to  employees of the Company  pursuant to the  Company's  Employee  Stock
Purchase 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 Plan (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  2,000,000  shares of Common  Stock that may be issued and
sold by the  Company  from  time to time  under the Plan,  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.
December 15, 2004
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