The combination of ifosfamide and mesna was evaluated in a phase II trial in the treatment of metastatic prostate cancer. Two separate groups of patients were to be evaluated: patients with no prior hormonal therapy and hormonally refractory patients. Patients were treated with ifosfamide 1.5 g/M2, and mesna at 30% of the ifosfamide dose was administered immediately before and 4 and 8 h after ifosfamide treatment. Both drugs were given i.v. daily for 5 days every 21 days. Response was assessed every 6 weeks. Of 29 eligible and evaluable patients with hormonally refractory disease, there were two partial responders for a response rate of 7% (95% confidence interval, of 0.1-23%). Of nine eligible patients with no prior hormone treatment, there was one partial response, for a response rate of 11% (95% confidence interval, 0.3-48%). Unfortunately, the target accrual goal for this arm of the study was never achieved. The most common toxicities were myelosuppression and neurologic toxicity. These drugs do not warrant further evaluation in the disease.