A new Doppler technique for assessing the fetal cerebral circulation is described. Cerebral blood-flow velocity was measured in 15 fetuses and 18 neonates of similar gestational age. The median fetal and neonatal velocities were 4.5 cm/s and 8 cm/s, respectively, with a larger range in the neonatal values. This technique is a noninvasive method of studying fetal cerebral physiology and may be of value in detecting intra-uterine asphyxia.