In a phase II study of vindesine in patients with bi-dimensionally measurable primary or metastatic prostate cancer, 27 patients (given 3 mg/m2 weekly for at least 4 treatment cycles) were evaluable for response 6 weeks from the start of treatment. Dose escalation to 4 mg/m2 weekly was attempted. Five patients (19%) achieved a partial remission of short duration, 11 patients (41%) showed no change and 11 patients (41%) showed progression. Thirty-one patients were evaluable for toxicity. Neurotoxicity occurred in 58% (severe in 23%) and was apparently cumulative dose-dependent, although there was variable individual sensitivity. Haematological toxicity was evidenced by lack of dose escalation in 32% of patients, dose delay in 71% and some degree of anaemia in 48%. Alopecia occurred in 55%. Other toxicities were few and minor. Vindesine shows marginal activity in prostatic cancer but at this dose schedule causes appreciable toxicity.