The goal of radioimmunotherapy (RIT) is to target radiation to tumor tissue with radiolabeled monoclonal antibodies while limiting toxicity to normal cells. Radionuclide emission properties and the chemical stability of radioimmunoconjugates are important factors that contribute to the effectiveness of RIT. A 1994 review of early clinical trials with RIT in treating non-Hodgkin's lymphoma (NHL) reported a 40% response rate with nonmyeloablative doses of yttrium 90 (90Y) or iodine 131 (131I) antibodies. Of the radiolabeled antibodies currently in pivotal trials or approved by the US Food and Drug Administration, those targeted to the CD20 antigen have produced the highest response rates. Response rates for ibritumomab tiuxetan, the recently approved RIT for NHL, ranged from 74% in rituximab-refractory patients to 80% in the pivotal trial. The iodine-labeled anti-B1 antibody has been evaluated in previously treated and previously untreated patients with NHL. In the pivotal trial, previously treated patients achieved a response rate of 65%, whereas previously untreated patients had a 97% response rate. Radiolabeled anti-HLA DR has been evaluated in NHL patients and has demonstrated a 53% response rate. Murine antibody LL2, which recognizes the CD22 antigen, has been radiolabeled with 90Y and 131I, with response rates ranging from 15% to 33%. The development of radioimmunotherapy has led to meaningful advances in the treatment of B-cell NHL.