The effects of naloxone hydrochloride (NAL) and other opiate antagonists on blood-ethanol concentration (BEC) in acutely-ethanol-intoxicated rats were examined. Using a 1 mg/kg body wt. dose of NAL, the maximum decrease in BEC was found to occur at 30 min. At 30 min after administration of various doses of NAL, it was found that BEC was decreased maximally by a 2 mg/kg dose, whereas the first significant decrease was caused by a 10 micrograms/kg dose. BEC was also decreased by naltrexone (1 mg/kg), but not by a 4 mg/kg dose of any of four Mr compounds (Mr 1452, Mr 1453, Mr 2266 and Mr 2267). It is suggested that pharmacokinetic antagonism of acute alcohol intoxication by naloxone and naltrexone is unrelated to the property of opiate antagonism, but may involve the ability of certain such antagonists to interact with hepatic NAD+-dependent oxidative metabolism.