Recent studies have indicated a neural regulation of hormonal and metabolic responses to exercise. Studies on the ventromedial hypothalamus (VMH) suggest that the VMH might be involved in neural control of exercise metabolism. We therefore studied 25 rats with or without Marcain-anesthetized VMH (Marcain and control rats, respectively) at rest or during treadmill running (26 m/min). The rats had cannulas aimed bilaterally at the VMH and chronic catheters in the left jugular vein and right carotid artery. At rest, glucose turnover and plasma concentrations of glucose, lactate, glycerol, epinephrine, norepinephrine, insulin, and corticosterone remained stable in control rats, whereas in Marcain rats these parameters, except for unchanged insulin and glucose utilization, increased after Marcain administration along with increases in hepatic and muscular glycogenolysis. During exercise, glucose turnover, hepatic and muscular glycogenolysis, and plasma concentrations of glucose, lactate, glycerol, catecholamines, and corticosterone increased, and insulin decreased in both Marcain and control rats. However, during exercise, initial hepatic glucose production, plasma catecholamines, and subsequent plasma glucose concentrations and overall hepatic glycogenolysis were lower in Marcain compared with control rats. In conclusion, glucose mobilization is enhanced by the VMH during exercise. The results suggest that decreased and increased activity in sympathetic inhibitory and facilitating VMH areas, respectively, are involved in the VMH's response to exercise.