Fifty-three high-risk pregnancies were followed up serially with Doppler velocimetry of the umbilical artery and uterine vessels from early on to investigate whether abnormalities in Doppler waveforms can predict the outcome of pregnancy accurately before other clinical signs develop. Results of Doppler velocimetry were withheld from the clinicians managing the patients. When the absence of end-diastolic velocities was first detected (in 13 fetuses) (AEDV group) there was no clinical difference between these pregnancies and those in which end-diastolic velocities were present (EDV group). Nine of the 13 fetuses with AEDVs died, compared with 3 of 40 with EDVs (P less than 0.0001). In deaths associated with AEDVs, the latter were detected a median of 5.5 (range 3-11) weeks before death and are present from the first Doppler examination. In the 4 fetuses with AEDVs that survived, the AEDVs were not persistent. The only significant association of Doppler velocimetry of the uterine vessels was with proteinuric hypertension (P less than 0.05), but the prediction was not strong enough to be of clinical value. Persistent AEDVs of the umbilical artery are an accurate predictor of poor fetal outcome and occur before other clinical signs of impending problems.