Some aspects of small intestine maturation have been studied in the newborns from chronic ethanol-treated pregnant rats (25% ethanol in drinking fluid) immediately after birth (before suckling) and after 30 days of life. Litters delivered by mothers fed ad libitum with a standard diet diluted 50% with cellulose were used as a nutritional control. At birth, pups from ethanol-treated mothers showed significant decreases in total intestinal length and thickness, low total lactase activity and low somatostatin intestinal content. The intestinal alterations of these neonatal parameters are not present in newborns from mothers on fiber-diluted diet. From delivery, pups from different experimental groups were nursed by normal lactating dams. At 30 days of age neither of those parameters differed among the groups. We propose that the low levels of total lactase activity in newborns from alcoholic mothers, that are a consequence of a lower intestinal mucosa content, are a direct effect of ethanol in utero on the fetal gastrointestinal system.