A 64-year old female had been diagnosed as having thrombotic thrombocytopenic purpura (TTP; Moschcowitz syndrome) in 1984. The initial episode and one recurrence 5 years later were successfully treated with fresh plasma transfusions without plasmapheresis. Two days before the present admission, she noticed pain in the knee and haematomas in both legs. Marked thrombocytopenia (9000/microliters), haemolytic anaemia (lactate dehydrogenase 1800 U/l, haemoglobin 7.8 g/dl, haptoglobin 5 mg/dl) and skin haemorrhages suggested a second recurrence of TTP. The blood film showed a massive increase in fragmented cells (more than 30 per field), microspherocytes and normoblasts. Thrombocyte values initially rose on daily treatment with plasmapheresis using membrane separation and fresh plasma exchange. However, after two attempts at stopping therapy, plasmapheresis and fresh plasma replacement failed to normalise thrombocyte values. The patient had a total of 44 plasmaphereses. Intravenous administration of three doses of 1.5 mg vincristine at intervals of 7 and 5 days combined with further plasmapheresis treatment soon led to normalisation of the thrombocyte count (320,000/microliters), a fall in lactate dehydrogenase (120 U/l) and a disappearance of fragment cells in the blood smear. The patient is still in complete remission 6 months after stopping treatment. Treatment with vincristine should be considered for TTP refractory to treatment.