The purpose of this study was to examine the influence of postexercise parasympathetic modulation, measured by heart rate variability (HRV), on heart rate recovery (HRR) in boys (n = 13, 10.1 +/- 0.8 years) and men (n = 13, 23.9 +/- 1.5 years) following maximal and submaximal exercise. Subjects completed 10 min of supine rest, followed by graded exercise on a cycle ergometer to maximal effort. On a separate day, subjects exercised at an intensity equivalent to ventilatory threshold. Immediately following both exercise bouts, 1-min HRR was assessed in the supine position. HRV was analyzed under controlled breathing during the final 5 min of rest and recovery in the time and frequency domains and transformed to natural log (ln) values. Boys had a greater 1-min HRR than men following maximal (58 +/- 8 vs. 47 +/- 11 beats.min(-1)) and submaximal (59 +/- 8 vs. 47 +/- 15 beats.min(-1)) exercise (p < 0.05). Following maximal exercise, boys had greater ln root mean square successive differences in R-R intervals (2.52 +/- 0.95 ms), ln standard deviation of NN intervals (3.34 +/- 0.57 ms), ln high-frequency power (4.32 +/- 2.00 ms(2)), and ln low-frequency power (4.98 +/- 1.17 ms(2)) than men (1.33 +/- 0.37 ms, 2.52 +/- 0.24 ms, 1.32 +/- 1.06 ms(2) and 2.80 +/- 0.74 ms(2), respectively) (p < 0.05). There were no differences in any HRV variables between groups following submaximal exercise (p > 0.05). In conclusion, it appears that greater parasympathetic modulation accounts for greater HRR following maximal exercise in boys versus men. Although submaximal HRR was greater in boys, parasympathetic responses were similar between groups.