Ninety-eight patients with non-Hodgkin's malignant lymphoma were first put into complete remission by a combination of chemotherapy and radiotherapy, and then received one course of chemotherapy as reinforcement. They were then randomized to receive either maintenance BCG therapy or no other treatment. Ninety-three patients were available for this analysis. There was a significant difference (P = 0.021) in relapse-free survival times between the two groups of patients. This difference is particularly significant in male patients, in patients ages 50-65 years, in all histologic classes, in patients treated after an initial relapse, and in clinical stages I and II. There was also a difference in crude survival, but the difference was not significant.