The hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP) are syndromes of microangiopathic hemolytic anemia dominated by renal failure in children and by neurological signs in adults. Microvascular thrombosis is the typical lesion and endothelial injury is likely the initial event. Over the last 40 years, the prognosis has significantly improved, probably as the result of better supportive management of anemia, renal failure, hypertension, and electrolyte and water imbalances, but still remains poor in adults with renal arteriolar thrombosis and neurological involvement. Many specific therapies have been used and, based on reports of a few cases, a consensus has been reached empirically that recognizes antiplatelet agents and plasma manipulation as the most appropriate therapy for adult HUS and TTP. Their effectiveness, however, still remains to be formally tested in prospective controlled trials. Recently, we saw a 23-year-old man with a history of recurrent episodes of HUS in childhood and of TTP since the age of 21. HUS always disappeared following blood transfusions, whereas prompt remissions of the episodes of TTP were obtained with plasma exchange. In order to avoid the use of plasma, alternate forms of therapy were tried. However, aspirin (50 mg/day), prednisone (1 mg/kg bw/d), and human immunoglobulins (0.5 mg/kg/d) were ineffective, and plasma exchange was needed to obtain remission. During two more recent relapses, fresh-frozen plasma was infused as the initial therapy and produced a complete remission within few days, thus preventing the need for plasma exchange. During the last relapse, plasma exchange with albumin and saline failed to induce remission and plasma infusion was required.(ABSTRACT TRUNCATED AT 250 WORDS)