Twenty one patients with hormone resistant prostate cancer were entered in a phase II study of pirarubicin 70 mg/m2, as a single intravenous injection given at 21 day intervals. All patients had leukopenia (9 severe or life threatening) and 2 died of septicemia. Thrombocytopenia occurred in 5 patients (one life threatening) and anemia in 12 patients. One partial response of 3 months duration was documented. Pirarubicin 70 mg/m2 given intravenously at 21 day intervals causes severe hematological toxicity and has minimal therapeutic activity in patients with hormone resistant prostate cancer.