Originally described in 1925 (1), thrombotic thrombocytopenic purpura remained until recently a fulminating and rapidly fatal disorder. Fortunately, it has been rare. For this reason, the early literature on the disorder has consisted of accounts of one or a few cases, largely descriptive and all attesting to the very high mortality rate; in accounts of some 23 cases, only three patients recovered. Very likely the mortality rate was even higher, because most authors prefer to report successes rather than failures. In these studies, patients failed to respond to low-dose corticosteroids, splenectomy, heparin, dextran, dipyridamole, and aspirin, given alone or in