The effects of chronic alcohol intake on menstrual cycle status and hormonal function were studied in 26 healthy, adult women under controlled research ward conditions. Women were classified as heavy, social or occasional alcohol users on the basis of the actual number of drinks consumed during 3 consecutive weeks of alcohol availability. Heavy, social and occasional users drank an average of 7.81 ( +/- 0.69), 3.84 ( +/- 0.19) and 1.22 ( +/- 0.21) drinks/day, respectively. This drinking pattern was highly consistent with subjects' self-reports of alcohol use before the study. No evidence of menstrual cycle dysfunction or abnormality in reproductive hormone levels was found in the occasional drinkers or in two of the social drinkers who consumed less than an average of three drinks/day. In contrast, 50% of the social drinkers who consumed more than three drinks/day and 60% of the heavy drinkers had significant derangements of menstrual cycle and reproductive hormone function. The major abnormality found in social drinkers was anovulatory cycles, and three of the five women who were heavy drinkers had persistent hyperprolactinemia. These findings suggest that alcohol-related menstrual cycle and reproductive hormone dysfunction may be more prevalent among women who are social and heavy drinkers than has been assumed previously.