25 patients with measurable or evaluable metastatic prostate cancer, progressive after hormonal treatment, were treated weekly with carboplatin 150 mg/m2 intravenously. The weekly schedule allowed higher dose intensity carboplatin administration with respect to the common monthly cycles. Toxicity was manageable even in elderly patients with extensive bone metastases and consisted primarily of myelosuppression. 4 out of 24 evaluable patients (17%) had a partial response and 12 (50%) had disease stabilisation. The median response duration was 7 months. Prostate-specific antigen and prostatic acid phosphatase serial values showed a correlation with disease response in only 47 and 50% of patients, respectively. These results suggest that carboplatin possesses a moderate but definite activity in prostate cancer patients.