The objectives of the project are to study factors affecting the regulation of uterine blood flow in primates, using the rhesus monkey as an experimental model. These factors include uterine contractions, steroid hormones, autonomic drugs and changes in the maternal arterial blood gases. Uterine artery blood flow will be measured with an electromagnetic flow meter. The effect of changes in uterine blood flow and other maternal physiologic changes on the fetus will be studied by means of chronically implanted catheters and electrodes. Fetal parameters to be measured include heart rate, blood pressure, fetal blood gas tensions and pH, fetal activity patterns and respiratory movements. The electromechanical phenomena of the fetal cardiac cycle will also be studied, particularly in reference to changes in maternal and fetal blood gas tensions.