44 eligible patients with measurable or evaluable metastatic prostate cancer were treated with monthly cycles of cisplatin and mitoxantrone. Good-risk patients received cisplatin 60 mg/m2 intravenously and mitoxantrone 10 mg/m2 intravenously every 4 weeks. The dose in poor-risk patients (elderly or white blood cell count less than 4000/microliters, 4 x 10(9)/l, or extensive prior radiation) was reduced to 8 mg/m2. Toxicity was manageable and consisted primarily of myelosuppression. There were no complete responses and the partial response rate was only 12%. Median progression-free survival was 2.7 months for measurable and 4.1 months for evaluable disease patients. Median survivals were 4.9 and 8.7 months, respectively. This combination has minimal activity in hormone refractory metastatic prostate cancer.