121 healthy premature born infants and full term newborns (corrected gestational age 29 to 45 weeks, weight at investigation 1070 to 3750 g) were investigated by pulsed Doppler sonography with a 5 MHz transducer. In all infants pulsed Doppler recordings were obtained from the internal carotid arteries (ICA), the basilar artery (BA) and both anterior cerebral arteries (ACA). From the flow profile the maximal systolic velocity (Vs), the endsystolic velocity (Ves) and the enddiastolic velocity (Ved), the time average velocity (TAV) and the time average maximal velocity (TAMX) as well as the resistance-index (RI) and the pulsatility-index (PI) were measured. For all parameters the relationship to the gestational age was analysed and normal values were established. There was a linear increase of all flow velocities with increasing gestational age. Vs in the ICA was about 20% higher than in the ACA and BA whereas Ves and Ved were not significantly different in the three arteries. The TAV in the ICA was 9% higher than in the ACA and 15% higher than in the BA. The TAMX in the ICA was 10% higher than in the ACA and 14% higher than in the BA. In contrast to the increase of the flow velocities neither the RI nor the PI showed a significant age dependency. For the RI in the ICA 0.77 +/- 0.08, in the ACA 0.73 +/- 0.08 and in the BA 0.72 +/- 0.09 were measured. The PI in the ICA was 3.0 +/- 0.08, in the ACA 2.7 +/- 0.09 and in the BA 2.7 +/- 0.7.(ABSTRACT TRUNCATED AT 250 WORDS)