A prospective randomized trial by CALGB examined the relative value of four chemotherapy regimens in 537 patients with stage III B and IV Hodgkin's disease. A new combination BOPP, derived by substitution of BCNU for nitrogen mustard in the MOPP regimen, was compared to MOPP and to two 3-drug regimens, derived by removing the procarbazine in BOPP (BOP) or removing the alkylating agent (OPP). The 4-drug programs gave significantly higher frequency of complete remissions (BOPP 67%, MOPP 63%) than the 3-drug regimens (BOP 40%, OPP 42%), and significantly longer duration of remission and survival. BOPP had a therapeutic activity equal to MOPP, and was accompanied by less toxicity. After 6 cycles of induction chemotherapy, responding patients, both CR and PR, were continued on maintenance chemotherapy for 3 years. No significant difference in relapse rate was demonstrated following maintenance treatment with either vinblastine, chlorambucil, or chlorambucil plus monthly vincristine + prednisone doses. Nor could a reinforcement phase late in the maintenance program be shown to influence the relapse rate. The median survival for all patients entered on the 4-drug programs was 5 years, while the median has not yet been reached at 6 years for those patients, who obtained CR.