One-hundred-and-fifty-one patients with previously untreated multiple myeloma were allocated to treatment with either NOP regimen (mitoxantrone 16 mg/m2 and vincristine 2 mg day 1 and prednisolone 250 mg day 1-4 and 17-20) or M+P regimen (melphalan 0.25 mg/kg and prednisolone 100-200 mg/day day 1-4). Both regimens were repeated every 4 weeks and were scheduled for 1 year. Seventy-seven patients were treated with NOP and 74 patients with M+P. No major clinical differences were recorded between the groups before treatment. Sixty percent of the patients responded (CR+PR) to NOP versus 64% to M+P (NS). The time to progression was 16 months (95% C.L. 14-51) in the NOP group versus 21 months (95% C.L. 15-27) in the M+P group (NS). The median survival was 14 months (7-21) in the NOP group and 31 months (21-43) in the M+P group (p = 0.02). NOP was significantly more toxic than M+P. Seven patients treated with NOP died due to infection and neutropenia and 1 patient died of cardiac toxicity, in contrast to 1 death due to infection and neutropenia in the M+P group. Gastrointestinal toxicity was acceptable in both groups. In conclusion, NOP was inferior to M+P as primary treatment of multiple myeloma.