Severe pulmonary edema was observed in two patients following blood transfusion reactions. The amount of blood transfused was small and there was no evidence of fluid overload in either patient. The roentgenographic appearance is one of bilateral patchy infiltrates suggestive of interstitial edema. Hemolysis of erythrocytes with release of substances causing constriction of pulmonary arterioles or venules, or intravascular coagulation are possible pathophysiologic mechanisms. Therapy consists of the usual respiratory support measures. Dextran 40, heparin sodium, and isoproterenol may be of benefit.