Heroin lung is the most frequent complication of heroin intoxication. In September 1991 and January 1993, two young men aged 19 and 22 years presented with a sudden loss of consciousness and cyanosis after injecting heroin. They were both brought to our emergency department in the night and were immediately intubated and given 100% oxygen. Following intravenous naloxone, they both regained consciousness. The first patient's chest X ray revealed increased bilateral perihilar lung markings and mild patchy alveolar edema while the second patient showed a bat's wing shaped confluent alveolar edema. The blood gases in both cases revealed hypoxemia and hypercapnia. Follow-up chest roentgenograms on the second hospital day in case 1 and the third hospital day in case 2 revealed partial clearing of the lung fields. Fever developed on the second hospital day and they both received two weeks of antibiotics prior to discharge. Case 1 had normal pulmonary function testing, but case 2 developed mild restrictive lung changes. Review of the literature shows that heroin can cause a fulminant but rapidly reversible form of pulmonary edema. The treatment for this noncardiogenic pulmonary edema is adequate ventilation, good pulmonary toilet, and naloxone to reverse the respiratory and central nervous system depression. Diuretics, digitalis and morphine are not recommended in the treatment of heroin lung.