The effects of alcohol (2.5 and 3.5 g/kg) on luteinizing hormone (LH) and testosterone were studied in adult male macaque monkeys under both basal and naloxone-stimulated conditions. Integrated plasma samples were collected at 30-min intervals for 90 min before nasogastric intubation of alcohol (2.5 and 3.5 g/kg) or a sucrose control solution, isocalorically equivalent to 2.5 g/kg of alcohol. Under basal (non-naloxone-stimulated) conditions, alcohol (2.5 or 3.5 g/kg) did not change LH levels significantly from prealcohol control levels. When basal testosterone levels were normal (600-1300 ng/dl), alcohol significantly suppressed testosterone levels in a dose-dependent manner. Testosterone levels decreased by 52% (P less than .05) within 30 min after a 3.5 g/kg dose of alcohol. As average blood alcohol levels increased to 400 mg/dl and above, testosterone levels fell monotonically and remained over 70% below base-line levels (P less than .01). After administration of 2.5 g/kg alcohol, testosterone levels were significantly suppressed within 90 min (P less than .05) and remained 52 to 63% below control levels (P less than .02-.05) as average blood alcohol levels increased to 300 mg/dl. However, when basal testosterone levels were abnormally low (100-200 ng/dl), alcohol had no effect on testosterone or LH. Naloxone stimulation was used to circumvent the high incidence of abnormally low testosterone levels observed. Naloxone (0.5 mg/kg i.v.) administration 90 min after alcohol (2.5 and 3.5 g/kg) or sucrose control administration significantly increased LH levels in comparison to base line (P less than .02-.001). LH reached peak values within 60 min after naloxone administration. A significant increase in testosterone (P less than .001) was observed 90 min after naloxone administration as LH levels began to decline. Alcohol (2.5 and 3.5 g/kg) did not attenuate or delay naloxone-stimulated increases in LH and testosterone in comparison to sucrose control conditions.