In a phase II study, 58 patients with resistant multiple myeloma (MM) were treated with a combination chemotherapy (NOP-bolus regimen) consisting of mitoxantrone (16 mg/m2 for the first 25 patients and 12 mg/m2 for the subsequent 33), vincristine (2 mg), both as bolus injections on day 1 and prednisone (250 mg/d on d 1-4 and 17-20). In patients greater than 70 years of age, the mitoxantrone dose was reduced to 12 mg/m2 or 8 mg/m2, respectively. The treatment was repeated every 4 weeks. A response (greater than 50% reduction in M component) was obtained in 26% of the patients and a minor response (clinical improvement but less than 50% reduction in M component) in another 21%. Median response duration was 27 wk and median survival for all patients was 25 wk. There were no differences in response rate or duration between patients receiving the high or low mitoxantrone dose, but patients in the low-dose group had fewer serious infections.