Using duplex Doppler ultrasonography in asymmetrically grown fetuses with decreased amniotic fluid, we found the renal artery waveform pattern was different from that in the normally grown fetus. Such an abnormal waveform may reflect an increase in vascular resistance within the renal bed in oligohydramnios and intrauterine growth retardation. This would suggest that local mechanisms are operational and may influence renal blood flow in the human fetus with intrauterine growth retardation.