Rats were fed a liquid diet containing ethanol from days 6-19 of gestation. Controls were pair-fed the same diet with sucrose substituted for ethanol, or received ad lib chow and water. The activity of the offspring was observed at 10, 16, 22 or 28 days-of-age. Overall, offspring exposed to alcohol prenatally were hyperactive compared to controls at 16 and 22 days, but not at 10 or 28 days. Administration of physostigmine had no effect on the activity of any group at 10 days. At 16 days, physostigmine enhanced the activity of the alcohol group, had no effect on the sucrose group, but depressed the activity of the chow group. At 22 days it led to a dose-related decrease in activity in controls but had no effect on the activity of the alcohol treated pups. At 28 days, physostigmine decreased the activity of all three groups. Administration of the quaternary derivative, neostigmine, indicated that the effects of scopolamine at 22 days were probably central in origin. These data indicate that a putative cholinergic/inhibitory system becomes functional in control pups before 22 days, but in pups exposed to alcohol prenatally development is delayed by a number of days.