The transfusion of blood and blood products is an im portant therapeutic procedure, but it is associated with several potentially serious adverse effects. Among these complications are hemalytic reactions, which in most cases result from the interaction between donor red cell antigens and recipient plasma antibodies. Clinical mani festations and sequelae are largely determined by the physical and immunological characteristics of the anti gens and antibodies. Early recognition may be difficult in the anesthetized or intensively monitored patient. Acute hemolytic reactions are responsible for significant morbidity and mortality and may lead to life-threatening shock, disseminated intravascular coagulation, and renal failure. Fortunately, fatal hemolytic transfusion reactions are rare; they usually result from clerical errors. Proper diagnosis and management requires sound clinical judg ment, thorough laboratory investigation, and timely therapeutic intervention.