The deleterious effects of ethanol on the hypothalamic pituitary growth hormone axis in adult male humans and animals have been well documented. It is also well established that ethanol has toxic effects on testicular function in adult humans and animals. Much less is known, however, about the effects of ethanol on the growth hormone (GH) axis and testicular function in adolescence. Recent studies have established that adolescent problem drinking is a widespread and growing threat to the health of young people in the United States. In the present study, therefore, we investigated if acute ethanol exposure in peripubertal male Sprague–Dawley rats altered normal pituitary and testicular function. Serum levels of GH and testosterone were measured at 1·5, 3, 6, and 24 h after a single i.p. injection of either saline or 3 g/kg body weight ethanol. Histologic analysis as well as serum testosterone levels allowed us to assign animals to either early puberty (35-day-old animals), mid-puberty (41-day-old animals), or young adult (51- and 66-day-old animals) status. Ethanol produced significant decrements in serum testosterone in the 51-and 66-day-old animals, with a trend toward suppression in the 41-day-old group. Furthermore acute ethanol administration significantly decreased serum GH (P< 0·0001 by 3 way ANOVA) demonstrating a significant effect of ethanol on serum GH in all age groups and at all time points studied when compared with saline injected controls (PJournal of Endocrinology (1997) 152, 477–487