Cerebral blood flow velocity (C.B.F.V.) was estimated in 49 newborn babies by calculating the pulsatility-index (P.I.) of the anterior cerebral arteries (A.C.A.) using Doppler ultrasound. We studied the changes in P.I. of the A.C.A. in relation to the clinical condition in three full-term babies with evidence of cerebral edema (in one patient proved by autopsy) due to perinatal asphyxia. There was a relation between the level of consciousness and the P.I.; a low P.I. (a sign of arterial vasodilatation) occurred with a low level of consciousness, while higher P.I. values (reduced vasodilatation) were detected when improvement of consciousness occurred. The following explanation is given: cerebral edema causes an increase of intracranial pressure and venous obstruction. The cerebral perfusion decreases and cerebral function changes; stupor and coma occur. By vasodilatation the resistance of the cerebral arteries is lowered; the C.B.F.V. increases in an attempt to restore cerebral perfusion. The vasodilation is reflected in the low P.I. values, as we found in our three patients.