Umbilical blood flow (UBF) and fetal glucose uptake were measured in 5 lamb fetuses 4–20 days following single umbilical artery ligation (SUAL). The ligation was performed at 108–119 days gestation (sheep pregnancy =145–150 days), and the blood flow and glucose uptake studies were performed as chronic preparation at 120–137 days of gestation. In comparison with 9 control subjects at matched gestation, the SUAL fetuses had significantly lower UBF (mean ± SEM, 735 ± 70 vs. 475 ± 24 ml/min, p < 0.01) and fetal glucose uptake (21.0 ± 1.6 vs. 14.8 ± 1.9mg/min, p < 0.05). When the values were expressed per kilogram fetal weight, the UBF decreased with increasing gestational age in SUAL fetuses. In the control fetuses, the UBF increased with increasing gestational age. The fetal glucose uptake (FGU), when expressed per kilogram fetal weight, was essentially similar to that of the control subjects. The glucose gradients across the placenta were similar in both groups of fetuses. These data suggest that in lamb fetuses with placental vascular insufficiency induced by SUAL, the reduction of UBF and FGU may account for growth retardation in utero. It was also suggested that placental transfer of substrate other than glucose may also be impaired as a result of reduced placental perfusion.