Severe heroin-induced pulmonary edema occurred in three previously healthy young men. Adequate arterial PO2 could only be achieved with the use of positive endexpiratory pressure (PEEP). Recovery was characterized by the gradual clearing of the pulmonary infiltrates and a gradual lessening of the severe restrictive ventilatory defects over many weeks. Concomitant aspiration of gastric acid was thought to be the explanation for the severity of these cases. In cases such as these, initial vigorous therapy, including PEEP for hypoxia, corticosteroids for possible aspiration and volume replacement for hypotension, is recommended.