A 53-year-old woman was admitted with a diagnosis of acute extensive anterior myocardial infarction. Pulmonary capillary wedge pressure was 17 mmHg, and cardiac index 2.4 l/min.m2. The patient was successfully treated with diuretics and nitrates but on the fifth hospital day moist rales were noted over the entire lung field. A chest roentgenogram showed diffuse bilateral pulmonary infiltration with unchanged cardiac silhouette. Arterial oxygen partial pressure was reduced to 45 mmHg under 3 liters of nasal oxygen inhalation. Pulmonary capillary wedge pressure was 8 mmHg. Diffuse infiltration was not ameliorated by intravenous injection of diuretics. The diagnosis of adult respiratory distress syndrome was finally established by successful treatment with steroids.