The study objective was to determine the acute effects of a moderate evening dose of alcohol on salivary melatonin levels in humans with stable prior sleep-wake histories and in a controlled environment. Twenty-nine adults (nine males) ages 21 to 25 (M=22.6, SD=1.2) yrs adhered to a 10-day at-home stabilized sleep schedule followed by three in-lab adaptation, placebo, and alcohol (order counterbalanced) study nights. Alcohol (vodka: 0.54 g/kg for men and 0.49 g/kg for women) or placebo beverage was consumed over 30 min, ending 1 h before stabilized bedtime. At 140 and 190 min after alcohol administration, melatonin level was reduced by 15% and 19%, respectively, in comparison to placebo. The findings indicate that a moderate dose of alcohol in the evening suppressed melatonin in young adults.