To the editor: We wish to report a severe hemolytic transfusion reaction from an extremely small amount of blood—specifically, 50 ml. The reaction was characterized by intravascular hemolysis, renal failure, and disseminated intravascular clotting; the latter was successfully treated with heparin. A 34-year-old white woman was admitted because of vaginal bleeding associated with an incomplete abortion. She was initially reported as having group A (negative) blood; transfusion of one unit of A negative compatible blood was begun. After receiving 50 ml, the patient became cyanotic and acutely dyspneic and complained of backache. The transfusion was stopped, and posttransfusion study showed