The effects of caloric restriction and exercise on resting metabolic rate (RMR) were studied in five obese humans. Subjects consumed a 500 kcal.d-1 diet for 4 wk, with the subjects remaining sedentary during the first 2 wk and then exercising 30 min daily at 60% VO2max during the last 2 wk of caloric restriction. After 2 wk of dieting, RMR decreased to approximately 87% of the pre-dieting control value. Over the last 2 wk of dieting with the addition of daily exercise, the fall in RMR was reversed as it returned to the pre-dieting level. In summary, daily exercise reversed the drop in RMR associated with severe caloric restriction.