Fifteen patients admitted to an intensive care unit for massive acute hemolysis (MAH), defined by a free hemoglobinemia of more than 60 mumol/l, were treated by plasma exchange (PE) after a mean period following onset of 48.5 39 hours. The aim of plasma exchange therapy was to obtain early purification of hemoglobin and other substances released by red cell lysis and to prevent serious complications of MAH such as shock and RVHF or acute renal failure. Treatment by PE produced a decrease in initial hemoglobinemia of 76%, this level then remaining stable. The PE also appeared effective in the prevention and treatment of shock and RVHF, but much less so for installed acute renal failure. Comparison of results with those of a previous series of 16 patients with MAH treated by exsanguino-transfusion showed that PE was more effective, simpler to perform and less aggressive for early treatment of MAH, if rigorous conditions are applied.