In 30 of 137 high-risk pregnancies we observed absent end-diastolic velocities indicating a high downstream impedance, which could be proved by histomorphological findings of the placenta. On the average the loss of end-diastolic velocities occurred 2–3 days before suspicious and nearly 8 days before pathological cardiotocographic findings. The perinatal mortality was high when absent velocities had been observed before the 32nd week, a cesarean section was obligatory in all but 1 case. All fetuses were growth-retarded. In 9 cases we were able to determine the ratio of blood flow volume in the common carotid arteries to that of the fetal aorta. The values were significantly increased as compared to values of undisturbed pregnancies, demonstrating a redistribution of fetal blood in favor of cerebral circulatio