This study investigated the effect of different exercise bouts on plasma leptin response. Trained men (n = 9) performed a short duration, maximal intensity (MAX) bout and a 60-min endurance run at approximately 70% of maximal oxygen consumption (END). Blood was collected before, immediately after, 24 h after (24 h Post), and 48 h after exercise (48 h Post) for measurement of plasma leptin, insulin, and glucose. VO(2)max and percent body fat were 57.8 +/- 2.1 mL x kg(-1) x min(-1) and 10.8 +/- 1.5% (mean +/- SEM), respectively. Energy expenditure was 197.5 +/- 11.8 and 882.7 +/- 14.4 kcal for MAX and END, respectively. Plasma leptin levels did not differ between time points for the MAX run. Leptin was significantly lower 48 h Post (2.2 +/- 0.3 ng/mL) versus before, immediately after, and 24 h Post exercise (3.1 +/- 0.3, 3.0 +/- 0.3, and 2.5 +/- 0.4 ng/mL, respectively) for END. Leptin tended to be lower at 24 h Post than before or immediately after exercise (P = 0.10). Plasma insulin was lower 24 h Post- versus preexercise for the END, but was not correlated to changes in leptin levels. Plasma glucose levels did not change significantly during the endurance test. We found a delayed decrease in leptin at 48 h after an extended exercise session (900 kcal). Furthermore, this effect did not appear to be related to changes in insulin or glucose levels. Findings from this study address the effects of exercise on leptin, aiding in the evaluation of the impact of exercise and energy expenditure on plasma leptin concentrations in the prevention and treatment of obesity.