The postnatal changes of cerebral blood flow velocity in 35 preterm neonates with or without complications were measured with a bidirectional Doppler flow meter. In the cases without complications, the pulsatility index for the anterior cerebral artery (ACA-PI) was high shortly after birth, and gradually decreased after 6 hrs as that in normal term neonates. However ACA-PI showed large variations in the cases with respiratory distress. On the other hand, ACA-PI in the cases with subependymal hemorrhage (SEH) was low during the first 6 hrs after birth, and thereafter showed no significant changes. ACA-PI in the cases with intraventricular hemorrhage (IVH) was high during the first 6 hrs after birth and then decreased when IVH was found on ultrasound scanning. ACA-PI increased gradually with progression of post-hemorrhagic ventricular dilatation. The difference of high PI in IVH and low PI in SEH during the first few hrs after birth suggests that the pathogenesis of SEH may be different from the mechanism of intraventricular rupture from SEH. Low PI values in the infants with SEH may be related to intrapartum events, while the changing patterns of high to low PI in the infants with IVH suggest postnatal hemodynamic changes.