Much progress has been made in the development and implementation of radionuclide-carrying antibody therapy (radioimmunotherapy or RIT) of non-Hodgkin's lymphomas (NHL) in the past decade. Response rates have generally exceeded 60% for nonmyeloablative single dose RIT (85% - 100% for myeloablative) in patients who have relapsed after primary therapy. It is also encouraging that the duration of such responses has often been greater than the response to the last chemotherapeutic regimen administered. These results, as well as a favorable toxicity profile, have resulted in the successful earlier and more widespread use of this new therapeutic modality. Although unlabeled antibody therapy alone has had a positive impact on the treatment of NHL, the response rates for RIT have been higher than (sometimes nearly double) those for unlabeled antibody therapy. This has been demonstrated in trials that have directly compared radiolabeled antibody with unlabeled antibody, as well as in separate trials for similar patient groups. Use of radionuclides in conjunction with antibodies adds transient marrow suppression and a small risk of second malignancy over unlabeled antibody therapy. However, the toxicity from a single course of RIT is very favorable compared to chemotherapy. Despite the enormous progress of RIT, much remains to be learned to fully optimize the role of this exciting modality in the treatment of NHL.