In recent years monoclonal antibodies have played an important role in cancer therapy. This successful track is grosso modo based upon developments in the production of desired antibody molecules, the identification of suitable tumor antigens and the construction of chimeric and fully humanized antibodies. Especially in hematologic disorders, notably in non-Hodgkin's disease, the monoclonal antibody rituximab has proven to be of value in relapsed or refractory disease. Yet, to overcome the nonoptimal properties of this drug, especially in relation to the time to next therapy, radiolabeled immunoconjugates have been synthesized. For this purpose, the radionuclide yttrium-90 has been linked to the monoclonal antibody ibritumomab via the chelator tiuxetan. The most recent clinical results of this radiolabeled agent versus the nonradioactive drug treatment are reviewed in this paper. Furthermore, attention is paid to the monoclonal antibody tositumomab labeled with iodine-131, of which the first clinical results have become available most recently. This overview also mentions possibilities to increase the therapeutic efficacy of radionuclide immunoconjugates. This can be achieved by enhancing the targeting characteristics of the antibody and the use of alpha radiation-emitting radionuclides.