The development of Doppler ultrasound evaluation of the uteroplacental and fetoplacental circulations is one of the most important achievements of modern obstetrics. For the first time, the obstetrician has the ability to evaluate, in a noninvasive way, circulatory systems critical to fetal development and the outcome of pregnancy and to obtain information of great value for the management of complicated pregnancies. At this time, Doppler examination of the umbilical artery has become a fundamental part of the evaluation of pregnancies complicated by retarded fetal growth. Doppler examination of the umbilical and uterine arteries has become the most accurate test to establish a fetal prognosis in patients with hypertension in pregnancy. Other indications for the use of this methodology (twins, diabetes, Rh isoimmunization, etc.) are being studied, and the role of Doppler ultrasound probably will extend significantly beyond the now well-established indications for its use.