Beer consumption by nursing women altered the sensory qualities of their milk and the behavior of their infants during breast-feeding in the short term. The infants consumed significantly less milk during the 4-hr testing sessions in which their mothers drank alcoholic beer compared to when the mothers drank nonalcoholic beer; this decrease in milk intake was not due to a decrease in the number of times the babies fed. Although the infants consumed less of the alcohol-flavored milk, the mothers believed their infants had ingested enough milk, reported that they experienced a letdown during nursing, and felt they had milk remaining in their breasts at the end of the majority of feedings. Moreover, the mothers terminated the feeds the same percentage of time on both testing days. The mechanism by which the consumption of alcoholic beer by lactating women decreases milk intake by their nurslings remains to be determined.