The internal carotid artery blood flow velocity waveforms were measured with continuous-wave Doppler ultrasound in 17 normal nonpregnant and 50 pregnant women. 1) The measurement of the blood flow velocities in the pregnant women revealed a characteristic pattern. That is, in the women in the early pregnant stage (less than 16 weeks' gestation, n = 13), the velocity was lower than that of nonpregnant women. In the middle pregnant stage (16 to 27 weeks' gestation, n = 18), the velocity became higher than in the early stage and in the late stage (equal to and more than 28 weeks' gestation, n = 19), it again became slower. 2) The initial systolic peak blood velocity (S1), end-diastolic blood velocity (d), time averaged maximal blood velocity (M), Pourcelot ratio (PR), systolic-diastolic ratio (S/D) and pulsatility index (PI) were calculated and did not show laterality in any group. 3) PR, S/D and PI of the women in the early stages of pregnancy were higher than those of nonpregnant women, indicating that the cerebral vascular resistance became higher in early pregnancy. This technique presented the possibility of the assessment of the cerebral blood circulation in pregnant women.