To clarify the usefulness of Doppler velocimetry in high-risk fetuses, i.e. with intrauterine growth retardation (IUGR) or with fetal distress, nomograms of the age-related changes in resistance and pulsatility indices in the fetal umbilical and middle cerebral arteries were made, and the best cut-off values for each parameter were determined. Included were 505 and 684 fetuses as the control and subject groups, respectively, between 22 and 41 weeks' gestation. Using the color-coded pulsed Doppler method, the resistance index in the umbilical and middle cerebral artery (RIUA, RIMCA), the pulsatility index in both these arteries (PIUA, PIMCA), and the RI and PI ratios between these arteries (RIUA/MCA, PIUA/MCA) were measured. In normal fetuses, RIUA and PIUA showed a gradual decrease with advance in gestational age. RIMCA and PIMCA showed a parabolic fashion with a peak around 30-31 weeks' gestation. RIUA/MCA and PIUA/MCA ratios decreased until 30-31 weeks' gestation and then increased to term. Analyses with receiver-operating-characteristic (ROC) curves revealed that PIUA is the most appropriate parameter in identifying IUGR under the cut-off point of 1.5 S.D., with a sensitivity, specificity, positive and negative predictive value, and accuracy of 60.6%, 93.3%, 75.2%, 87.6%, and 85.0%, respectively. As for fetal distress, the PIUA/MCA ratio was the most efficacious parameter under the cut-off point of 2.0 S.D., with a sensitivity, specificity, positive and negative predictive value, and accuracy of 67.3%, 97.4%, 72.9%, 96.7% and 94.6%, respectively. The findings obtained indicate that the measurement of PI value in the umbilical artery is enough to detect IUGR per se, probably due to the reflection of the decrease in the placental vascular bed, and that the ratio of indices between the umbilical artery and middle cerebral artery is more accurate than independent evaluations in identifying fetuses developing fetal distress, reflecting a brain sparing effect as well as fetoplacental insufficiency.