The effects of the alpha-adrenergic agonists, norepinephrine and methoxamine, and the alpha-antagonist, phenoxybenzamine, on umbilical and uterine blood flows, fetal and maternal heart rates, arterial and venous pressures were examined in near-term chronic sheep preparations. Norepinephrine injection or methoxamine infusion to either fetus or ewe resulted n a respective unilateral fetal or maternal pressur response associated with bradycardial. Uterine blood flow decreased significantly with alpha-agonist administration to either fetus or ewe. Umbilical blood flow did not change with either, but an increase in calculated umbilicalo vascular resistance did occur after fetal administrations of the alpha-agonist. Thus, both the uterine and umbilical vascular beds are responsive to alpha-agonism, but maternal uteroplacental perfusion appears to be more sensitive. alpha-Blockade in either fetus or mother produced no significant changes in umbilical or uterine blood flows or fetal or maternal perfusion pressure suggesting that basal alpha-adrenergic tone is unnecessary for normal maintenance of either fetal or maternal uteroplacental circulation.