Abstract: The present invention provides a method to achieve radioisotopic localization at tumor sites, i.e., a method of enhancing radiolabeled ligand localization to a tumor in an individual in need of such treatment, comprising the steps of: transducing the tumor with a gene encoding a membrane expressed protein unique to the tumor; and administering to said individual a radiolabeled ligand which specifically binds to the protein. The use of gene therapy technology to induce expression of high affinity membrane molecules/receptors can enhance the specificity of radioisotope localization while the use of radioactive isotopes with the ability to deliver radiation damage across several cell diameters will compensate for less than perfect transduction efficiency.