AbstractTwo patients with thrombotic thrombocytopenia purpura (TTP) are described in whom vincristine administration appeared to play a role in successful outcomes. The first patient with chronic TTP responded partially to plasma exchange followed by plasma infusion and transiently to splenectomy, but developed a complete long lasting remission after a single injection of intravenous vincristine. The second patient developed a complete remission following vincristine administration and plasma exchange. Although vincristine's mechanism of action in TTP is obscure, we suggest that vincristine is effective in the treatment of this infrequent and often fatal disease.