[en] The development of radiolabelled monoclonal antibodies has initiated an expansion of research in nuclear medicine. These new radiopharmaceuticals give promises to reach a long seeking goal, namely to produce tissue specific radiopharmaceuticals, directed against molecular sites of the cells, for diagnosis and therapy. Very few published papers, however, have been focused on the dosimetry, coupled with radiobiological considerations. The aim of this paper is to review the most important parameters necessary to take into consideration, for radioimmunotherapy planning