The effects of acute and chronic alcohol administration on serum testosterone and luteinizing hormone (LH) levels were examined in the male rat. Chronic alcohol administration resulted in depressed serum testosterone and LH levels when alcohol-fed rats were compared with rats maintained, ad lib, on rat chow and water. However, neither testosterone nor LH levels were significantly lower in alcohol-treated rats when comparisons were made to pair-fed control animals, indicating that the nutritional deficits imposed by the chronic alcohol-feeding regimen contributed heavily to the observed reductions in the 2 hormones. To avoid the problems associated with a chronic drug delivery model, rats were injected with a single acute injection of alcohol. LH levels dropped significantly within 2 h after the injection of a 2.5 g/kg dose of alcohol and remained depressed, at a level between 25-30% of control values, from 2-4 h. By 6 h after the injection, LH levels had returned to base-line levels. Testosterone levels were also reduced by alcohol, but this drop was not significant until at least 3 h after the injection. Testosterone levels did not return to control levels throughout the 6-h course of the experiment. Dose-response determinations revealed that alcohol produced a biphasic effect on serum testosterone and LH: low doses of alcohol significantly increased testoserone and LH, whereas high doses decreased the levels of hormones. The ability of alcohol to depress serum testosterone levels, and thus produce symptoms of hypogonadism in the male of several species, is possibly due to a primary effect of alcohol on the hypothalamic-pituitary aspect of the hypothalamic-pituitary-gonadal axis.