OBJECTIVES To present the rationale for and development of radioimmunotherapy (RIT) for non-Hodgkin's lymphoma (NHL), which culminated in the FDA's approval of yttrium 90 (90Y) ibritumomab tiuxetan in February 2002. DATA SOURCES Published clinical trials of 90Y ibritumomab tiuxetan and secondary literature on immunotherapy, RIT, and NHL. CONCLUSION Monoclonal antibodies to the CD20 antigen have become an accepted therapy for NHL. Factors such as the poor vascularization of some tumors and the variable expression of the antigen can mitigate the efficacy of monoclonal antibodies, which prompted the development of a new strategy, RIT. IMPLICATIONS FOR NURSING PRACTICE Knowledge of the background and development of RIT is essential for nurses to educate and manage patients with NHL.