Though thrombotic thrombocytopenic purpura (TTP) is not a common disorder, having an estimated annual incidence of one per million population, it merits attention.1First, it afflicts those in the prime of life between the third and fourth decade. Second, it generally runs a fulminant course with mortality in excess of 8096. Third, the recent introduction of plasma infusion and plasma exchange as a therapeutic mode significantly improves the outlook, giving a response rate of 70% to 90%. Originally described by Moschcowitz2in 1925 as an "acute febrile pleiochromic anemia associated with the presence of widespread microvascular occlusive thrombi," the etiology of TTP is still unknown, and the nature of the microvascular thrombotic lesion has been the object of many studies. Throughout the body, short segments of small arterioles and capillaries are partially or completely occluded by hyaline thrombi. Histochemical, immunologic, and ultrastructural findings indicate that the hyaline material