This study was conducted to determine whether acute alcohol consumption in near-term pregnant rats results in constriction of the fetal ductus arteriosus (DA). Twenty milliliters per kilogram of 30% (v/v) alcohol was administered via a stomach tube 0.5, 2, 4, 6 and 12 h prior to cesarean section and fetal sacrifice, at 1.00 p.m. on the 20th gestational day (day 20.5), in experimental groups A1-A5, respectively. Controls were given water alone. The calibers of the DA and pulmonary artery (PA) were measured using the whole-body freezing method with direct exposure of the DA and PA by shaving the frozen chests of the fetuses. The DA was significantly constricted 30 min after alcohol treatment. The constriction was also observed in groups A2-A4, but not in group A5. The PA was also less markedly but significantly constricted 30 min after alcohol administration, but groups A2-A5 showed normal PA caliber. It is concluded that alcohol has a constrictive effect on the DA when administered close to the end of gestation in the rat.