Radioimmunotherapy (RIT), a therapy targeted to tumor cells, is a modality that can currently deliver radiation to tumor cells at levels 3-50-times higher than to the normal tissue with the next highest dose. RIT appears promising for future cancer therapy. Clinical responses in patients with advanced cancer have frequently been achieved with RIT as a single agent. Extended complete remissions and even increased survival have been achieved in lymphoma. Similar results in other cancers seem likely with RIT in combination therapy.