In 70 intrauterine growth-retarded (IUGR) fetuses with antepartum late heart rate decelerations recordings of velocity waveforms of the umbilical artery were made with Doppler ultrasound and calculated as pulsatility indexes (PI). In 29 of these fetuses longitudinal recordings were made. Abnormal PIs preceded the occurrence of late heart rate decelerations in 27 (93%) of the 29 fetuses. The median duration of the interval between the first abnormal PI and the first appearance of antenatal heart rate decelerations was 17 days (range 0-60 days). This wide range can mainly be attributed to the gestational age at which the first abnormal velocity wave-form was recorded; during early gestation the interval was much longer than later in pregnancy. Absent end-diastolic velocity (AEDV) was found in 17 of the 29 fetuses (59%) and preceded the occurrence of decelerations with a median interval of 12 days. In the total group, 4 of the 70 IUGR fetuses with antepartum decelerations had a normal velocity waveform of the umbilical artery. Fetuses with AEDV (n = 45) were more severely growth retarded and were delivered at an earlier gestational age than those with end-diastolic velocity (n = 25). Also perinatal mortality and morbidity were higher in the group with AEDV. Yet, when fetuses were matched for gestational age and birth weight no differences in perinatal outcome were found in the groups with and without end-diastolic velocity.