Doppler blood flow velocity waveforms in the umbilical artery and fetal internal carotid artery were recorded in a total of 10 patients with severe intrauterine growth retardation (IUGR) and marked oligohydramnios to establish a fetal or utero-placental origin of IUGR. Gestational age varied between 28 and 37 wk. Negative maternal serology ruled out fetal infections. In six patients, IUGR was associated with abnormal flow velocity waveforms, indicating utero-placental insufficiency. Following delivery, these infants showed no structural defects; moderate to marked placental infarction was documented in 4 out of 6 cases. In the remaining four patients, IUGR was associated with normal flow velocity waveforms, suggesting a fetal origin of the IUGR. Following delivery, all four infants revealed structural defects, only one of which was diagnosed prenatally. Twice an abnormal karyotype was the underlying cause. There was no placental infarction. These preliminary data suggest that combined recording of the flow velocity waveform in the above-mentioned vessels may provide valuable additional information as to the cause of IUGR and as such be helpful in determining obstetric management.