We have previously shown that during swimming muscular glycogen breakdown was diminished and plasma glucagon and insulin were lower and higher, respectively, in adrenodemedullated rats compared to controls. These findings might be due to a lower work intensity or higher efficiency in adrenodemedullated rats than in controls. Furthermore, they might be due to either an acute or a chronic influence of epinephrine. Rats were adrenodemedullated (DM) or sham-operated (C). They were chronically cannulated and either rested or ran in a metabolism chamber for 45 min. Running DM rats had either saline (DM-S) or epinephrine (normalizing the concentration in plasma) (DM-E) infused. During running, oxygen uptake was identical in C and DM rats. Muscular glycogen breakdown was similar in DM-E and C rats and higher than in DM-S rats. Blood glucose, lactate, and heart rate increased in C and DM-E, but not in DM-S rats. In spite of the differences in blood glucose, plasma insulin was the same in all groups and plasma glucagon increased identically in all running rats. Plasma FFA and liver glycogen were similar in all groups. In conclusion. in running rats, epinephrine exerts an acute enhancing effect on muscular glycogenolysis, glucagon secretion, and heart rate and an acute depressing effect on insulin secretion.