Single breath diffusing capacities for carbon monoxide (DLco) were measured in 12 normal supine subjects before and after ingestion of 15 to 30 ml of 95 percent ethanol (ETOH) to determine if alcohol could acutely change the DLco. Both DLco and specific DLco (DLco/alveolar volume) were significantly decreased 90 minutes after the ingestion of alcohol. This change may be due to a direct effect of alcohol on the alveolar capillary interface by possibly interfering with a carbon monoxide carrier molecule. Another plausible explanation for the reduced diffusing capacity after ingestion of alcohol may be redistribution of blood from the lung to the periphery secondary to the hemodynamic effects of alcohol.