Slices of uterine muscle from pregnant rhesus monkeys, Macaca mulatta, were incubated in medium containing [1-14C]glucose and [6-14C]glucose. The Qo2, glucose uptake, and lactate and CO2 production were similar at 92 days (55% of gestation) and 155 days (93% of gestation). The data suggest that glycolysis is a more important pathway in pregnant rhesus myometrium than in skeletal muscle. However, only about 0\m=.\2% of the glucose uptake could be accounted for by oxidation via the pentose cycle. Glycogen appeared to be important as an energy reserve during myometrial growth. There was an increase in glycogen levels from the 54th to the 92nd day of gestation but no evidence that the glycogen level or turnover rate increased near term. The low respiratory quotient (0\m=.\7) and the small amount of [14C]glucose oxidized to CO2 by way of the citric acid cycle (less than 2% of the glucose uptake), plus the fact that only 5% of the respired CO2 was produced from [14C]glucose suggest that the major energy-source for resting myometrium is lipid rather than carbohydrate.