Forty-eight male rats either underwent sterotaxic placement of electrolytic lesions in the ventromedial nucleus of the hypothalamus or had a sham operation and, after a recovery period of at least two weeks, were assigned to either a trained or untrained condition. Training consisted of treadmill running for 120 min per day, 5 days per week, for 12 weeks. At which point all rats were sacrificed to allow the determination of carcass analysis and fat pad lipolysis rates. Both untrained and trained animals with lesions had significantly increased carcass fat. The increased fat content not be attributed to an increased intake since the average daily food consumption of the four groups was not different. Training significantly reduced the fat content in both the lesioned and unlesioned rats. However, the loss in the lesioned rats was about one third less than that of the unlesioned. Training also increased the rate of lipolysis irrespective of whether an animal was lesioned or not. However, the amount of increase was about one third less than in trained normals. Destruction of the ventromedial nucleus of the hypothalamus apparently does not destroy the ability of exercise to alter body composition. The lesions may diminish the capacity of endurance programs to reduce carcass fat. Since the findings relative to lipolysis result from an in vitro investigation, they do not necessarily reflect the events occurring in the in vivo state.