The acute effect of opioid antagonists on volitional ethanol intake was studied in unselected Sprague-Dawley rats using a two-bottle, free-choice model. The total daily intake of ethanol during saline treatment was 1.79 ± 0.4 g/kg/day (n= 136). The rats were deprived of fluids for the last 4 hr of the light period. Saline or drug was given intraperitoneally 20 to 30 min before the onset of dark, and the ethanol and water intakes were measured during the following hour. The ethanol intake during this hour was 0.75 ± 0.06 g/kg (n= 136). Naltrexone significantly reduced ethanol intake. There was also a signiflcant reduction in ethanol Intake following administration of ICI-174,864. Naloxonazine and naloxone methiodide lacked effect. None of the treatments had any effect on the water or food intake. The resutts suggest that central bopioid receptors modulate volitional ethanol intake in the rat.