To determine the role of fetal swallowing in the control of amniotic fluid volume and composition and fetomaternal sodium transport, 4 ovine fetuses of 101-129 days' gestation had their esophagi surgically occluded. Amniotic and fetal vascular cannulas were implanted at the same time in these fetuses and in four intact controls. There was no difference between the amniotic sodium or potassium of these two groups over the next 3 weeks, at which time cesarean section was performed and the volume of amniotic fluid measured. Hydramnios did not result from esophageal atresia. Twenty-four hours after injection of 24Na into the amniotic fluid, the percentages of the dose in the fetal/ maternal compartment were similar in intact and esophagus-ligated fetuses.