[en] In order to evaluate some of the key factors that may allow the optimization of radiolabeled monoclonal antibodies when used as diagnostic and therapeutic tools to detect and treat human neoplasia, we studied three approaches: (a) we compared the biodistribution of the anti-lung-tumor monoclonal antibody KS1/4, labeled with four different radionuclides, in athymic (nu/nu) mice bearing a human lung tumor; (b) we fragmented the MoAb KS1/4, labeled its two antigen-recognizing fragments and compared their biodistribution in the tumor-bearing mice and (c) set-up conditions for performing analyses that have to be considered when deciding which radionuclide should be chosen to label a given MoAb. (author)