Studies in man on the effect of ethanol on growth hormones (GH) release have been inconclusive. In order to investigate the effect of ethanol on spontaneous episodic secretion of GH, rats were implanted with chronic carotid catheters to permit frequent sampling in unanesthetized rats. Secretion during the 3 hr before (0--180 min) and after (181--360 min) ethanol or saline was assessed by means of samples drawn every 15 min. Secretion patterns after saline or ethanol 0.5 and 2 g/kg were indistinguishable, but ethanol in doses of 3 and 4 g/kg abolished rat GH (rGH) secretion in a majority of animals. Mean rGH after saline injection for the period 181--360 min was 62 +/- 9 ng/ml. When ethanol was given, mean rGH values for this time period were 0.5 g/kg, 63 +/- 6 ng/ml; 2.0 g/kg, 47 +/- 7 ng/ml; 3 g/kg, 28 +/- 3 ng/ml; and 4 g/kg, 23 +/- 2 ng/ml. Differences were not statistically significant between saline and 0.5 or 2 g/kg ethanol, but were significant (p less than 0.01) for 3 or 4 g/kg ethanol. Thus, a single dose of ethanol can abolish spontaneous rGH secretion, but it must be a high dose. The effect of chronic ethanol administration remains to be investigated.