Vincristine (1.4 mg/m(2) on day 1, followed by 1 mg on days 4 and 7) was given to eight patients with thrombotic thrombocytopenic purpura (TTP) who were refractory to plasma exchange (n=4) or plasma infusion (n=4). Seven of eight patients (87%) achieved a complete response; one was refractory to treatment and died within a few weeks. After a median follow-up of 50 months, all responding patients are alive and well. Two patients relapsed and were successfully retreated with vincristine. Toxicity was mild, consisting of two episodes of leukopenia and one of autonomic neuropathy leading to paralytic ileus in a patient aged 70 years. We conclude that vincristine is highly effective in the treatment of patients suffering from refractory TTP, with negligible toxicity.