Radioimmunotherapy with anti-CD20 antibodies is a promising treatment approach for relapsed low-grade non-Hodgkin's lymphoma. Under revised Nuclear Regulatory Commission regulations (May 1997), patients may be released following treatment provided the maximum dose to any individual is not likely to exceed 500 mrem. Non-Hodgkin's lymphoma patients have been studied to evaluate radiation exposure to caregivers/family members after outpatient treatment with tositumomab and iodine I 131 tositumomab (Bexxar therapy). Estimates of total radiation doses to individuals expected to be maximally exposed to patients posttreatment have revealed that the doses should be within revised guidelines. In a University of Nebraska Medical Center study, the predicted total radiation doses (based on patient dose rate at 1 meter) ranged from 95-423 mrem. Family members were provided radiation-monitoring devices to directly monitor radiation exposure. Measured doses ranged from 10-409 mrem. In this and other studies, estimated and measured dose equivalents to maximally exposed individuals were below 500 mrem. Measured doses were, in most instances, lower than those predicted by patient-specific calculations, thus confirming the validity of the calculated dose predictions. Therefore, radioimmunotherapy with tositumomab and iodine I 131 tositumomab can be safely conducted on an outpatient basis.