The reported effects of alcohol on lung and brain phospholipid metabolism in adult animals have been numerous, but its effect on the fetal lung has not been examined. We investigated the effect of heavy maternal ethanol intake on fetal pulmonary maturation, as measured by the amniotic fluid phospholipids, lecithin and phosphatidylglycerol (PG). Mothers were screened at their first prenatal visit, and detailed drinking histories were taken. Amniotic fluid phospholipids were determined later in pregnancy for clinical purposes, and mothers with positive scores who admitted to drinking during the third trimester were compared to a control group. Amniotic fluid from mothers whose fetuses were exposed to ethanol late in pregnancy did not show the expected increase in lecithin/sphingomyelin and PG related to gestational age that was observed in nondrinking mothers. Canonical correlation of gestational age, late pregnancy drinking, and chronic alcohol problems with amniotic fluid L/S and PG jointly revealed that both gestational age and maternal drinking were significant determinants of fetal lung maturity (r = .39, P less than .05), with active maternal drinking being about one-third as important a determinant as gestational age. These findings could be explained by the known damage-inducing effect of ethanol on alveolar cell membranes or by the effects of ethanol on phospholipid metabolism.