Ten chronically instrumented pregnant ewes were studied to assess the effect of an epinephrine-induced decrease in uterine blood flow on the oxygen uptake of the uteroplacental-fetal tissue mass. Additional measurements of maternal cardiac output, oxygen uptake, arterial pressure, and hematocrit were obtained. Continuous systemic infusion of epinephrine at a rate of 0.3 to 0.4 microgram per kilogram per minute produced a mean decrease in uterine blood flow of 42 per cent (288 +/- 15 to 157 +/- 8 ml.per kilogram per minute). However, the oxygen uptake of the uteroplacental-fetal tissue mass remained at control levels due to an associated 79 per cent increase in the arteriovenous oxygen content difference across the uterine circulation. The calorigenic and cardiovascular systemic effects of epinephrine (a 22 per cent increase in maternal oxygen uptake and a 43 per cent increase in maternal cardiac output) were not related to the changes in either uterine flow or oxygen uptake. The implications of these observations are discussed.