Clinical trials of immuno-chemotherapy were conducted on malignant lymphoma patients. Patients during the period from 1972 through 1977 were allocated to two groups retrospectively according to the mode of treatment, i.e., chemotherapy alone (historical control group, 35 patients) and chemotherapy with OK-432 (treated group, 15 patients). Comparisons were made of the two groups, which were homogeneous with regard to induction chemotherapy, maintenance chemotherapy, stage and histologic type of disease. The treated group had a higher remission rate, and a longer remission duration and survival than the control groups, especially in patients with Hodgkin's disease but the difference was not statistically significant owing to the limited number of cases.