Thrombotic thrombocytopenic purpura and adult hemolytic-uremic syndrome (TTP/HUS) have a substantial mortality rate even with currently available treatments. Although therapeutic plasma exchange is the recommended treatment of TTP/HUS, this cumbersome procedure may not be available for all patients in an emergency. In this context, plasma infusion may represent an alternative first-line therapy. We compared the effectiveness of high-dose plasma infusion (25-30 mL/kg per day) and therapeutic plasma exchange as first-line treatment of adult TTP/HUS at a single center. Two groups of patients with TTP/HUS were identified according to their initial therapy, that is, high-dose plasma infusion (19 patients) and therapeutic plasma exchange (18 patients). Clinical charts and outcomes were retrospectively analyzed. Endpoints for comparison were the duration of platelet counts below 150 x 10 /L and LDH levels above normal values; the volumes of plasma administered and the duration of treatment; complete remission, relapse, and mortality rates; and treatment-related complications. Patients of the 2 groups had comparable clinical and laboratory features on admission. Sixteen patients achieved complete remission in each group. Median times to recovery of platelet counts and LDH levels were comparable between the 2 groups. Eight patients in the high-dose plasma infusion (HD-PI) group were switched to therapeutic plasma exchange because of fluid overload (6 patients), persistent biologic disturbances (1 patient), or unresponsiveness to high-dose plasma infusion treatment (1 patient). This latter patient had severe TTP/HUS that remained refractory to therapeutic plasma exchange and vincristine, and rapidly died. All 7 remaining patients achieved complete remission with therapeutic plasma exchange. Four patients in the HD-PI group and 3 patients in the therapeutic plasma exchange (TPE) group died. In the HD-PI group, 5 patients experienced a transient nephrotic-range proteinuria during treatment. Main complications in the TPE group were collapse (1 patient) and central venous catheter infection (2 patients) or thrombosis (1 patient). Three patients in each group relapsed. High-dose plasma infusion may be an efficient treatment of TTP/HUS in patients who cannot have early plasma exchange. However, the large volumes of plasma required to reach complete remission may result in fluid overload, which may necessitate subsequent therapeutic plasma exchange.