The effects of acute alcohol ingestion were studied on pulsatile secretion of immunoreactive luteinizing hormone (LH), follicle-stimulating hormone (FSH), and growth hormone (GH), and on serum bioactive LH, testosterone, cortisol, and prolactin. A dose of 1.5 g ethanol per kg of body weight was administered by mouth to eight healthy male volunteers (aged 20 to 26 years) during 3 hr from 1800 to 2100 hr. Blood samples were collected every 20 min for 20 hr until 1400 hr of the following day. Each subject served as his own control in an identical experiment without ethanol, carried out at least 1 month later. Ethanol ingestion decreased serum testosterone concentration on average by 23% (p less than 0.05) between 10 and 16 hr after starting the drinking. The mean levels of LH and FSH and the mean number and amplitude of LH and FSH pulses remained unchanged. Ethanol ingestion did not affect the biological activity of LH. In each subject alcohol administration reduced the nightly peak of GH secretion, and in addition, changed the timing of this peak in most subjects. Only marginal changes were found in the prolactin levels but ethanol ingestion increased the cortisol levels on average by 36% (p less than 0.05) between 11 and 14 hr after the start of drinking. We conclude that the decrement in serum testosterone evoked by ethanol is not attributable to impaired pulsatile secretion of gonadotropins nor to reduced biological activity of LH. In contrast, ethanol profoundly suppressed the pulsatile secretion of growth hormone.