At New York University Medical Center over the past 18 months, a distinctive and potentially lethal syndrome of fulminating noncardiogenic pulmonary edema has been observed in three patients following cardiopulmonary bypass. The clinical appearance is virtually identical to that produced by acute left ventricular failure, and the condition could have been diagnosed incorrectly in the past as myocardial infarction with left ventricular failure and pulmonary edema. Thus it is uncertain whether this is a new syndrome or whether it has long been present. Fulminating noncardiogenic pulmonary edema can be diagnosed by finding a low left atrial or pulmonary artery wedge pressure combined with a high protein content in the pulmonary edema fluid when compared to simultaneous measurements of the plasma protein level. As no other etiologic agent could be identified in our three patients, the probable cause seems to be an unknown type of allergic reaction to blood or blood products, manifested by acute pulmonary edema—the pulmonary capillary membranes being the first to be exposed to fluids administered intravenously. The significant point is that a nearly fatal degree of pulmonary congestion can be managed safely and effectively with corticosteroids, antihistamines, positive-pressure ventilation, diuretics, and albumin. Presently, two important questions remain: (1) Should fluids be restricted and balloon pump counterpulsation and vasopressors utilized to maintain systemic pressure? (2) How long after administration of steroids is it safe to give intravenous albumin? Meanwhile, both the mechanism and frequency of this syndrome remain unknown.