A study was made of the interexaminer variability of Doppler velocity waveform determinations of the fetal circulation. Three investigators recorded Doppler ultrasound tracings of the blood velocity in the fetal thoracic and abdominal aorta and umbilical artery in 23 uncomplicated pregnancies. Of these recordings, a hard copy was made, and the pulsatility indices were computed. An analysis of variance was performed and the reliability calculated. The interexaminer variability was nonsignificant in measurements of the three blood vessels under examination. Both thoracic and abdominal aorta measurements showed poor reliability (intraclass correlation coefficient of reliability 0.30 and 0.19, respectively) due to high random errors. Umbilical artery measurements showed a better reliability (intraclass correlation coefficient of reliability 0.61), and, therefore, these hold the greatest clinical applicability.