A total of 171 patients with progressive metastatic prostate cancer following hormonal therapy was randomized to receive either 560 to 700 mg. estramustine orally per day or 15 mg./m.2 mitomycin C by intravenous infusion every 6 weeks. The patients were recruited during a 2.5-year period, and 70% had undergone more than 1 previous therapy for prostate cancer, with some having received as many as 5 different previous treatments. The overall results were disappointing. The median time to progression was 5 months and 50% of the patients died within 10 months. There was no difference in efficacy between the 2 treatment arms. Toxicity was severe in both arms but appeared earlier in those patients receiving estramustine, leading to a tendency for earlier deterioration in performance status. In this group of heavily pretreated patients there appears to be no justification for the use of either of these agents at the present time.