The purpose of this study was to investigate the effect of exercise training on meal-induced thermogenesis in 30 female subjects with an average age of 26 years, an average weight of 53.5 kg, and an average height of 162.4 cm. Three groups of 10 subjects were formed with an average maximum aerobic capacity (VO2max) of 57.5 mL X kg-1 X min-1 and a percent body fat of 17.5% for group 1 (competition athletes), of 49.9 mL X kg-1 X min-1 and 21.2% for group 2 (moderately active), and 38.9 mL X kg-1 X min-1 and 22.2% for group 3 (sedentary subjects). Oxygen uptake (VO2), respiratory quotient (R), and heart rate (HR) were measured at intervals for 45 min before and 120 min after a standard meal containing 800 kCal (1 kCal = 4.184 kJ). The increases in VO2 produced by the meal were significantly smaller (P less than 0.05) in group 1 than in group 3. Following the meal, R was significantly increased (P less than 0.01) from its initial value in the three groups, but it remained significantly lower in the well-trained subjects than in the nontrained. HR, which was initially higher (P less than 0.01) in group 3, was slightly increased after the meal, but the response was the same for all groups. These results show a diminished meal-induced thermogenesis in exercise-trained female subjects associated with reduced carbohydrate oxidation.