In adults, serum and salivary cortisol increase during aerobic exercise. There is little data on serum and no data on salivary cortisol responses during aerobic exercise in children. The purpose of this study was to examine serum and salivary cortisol during and after aerobic exercise. Ten male children with a mean age of 10.6 ± 0.6 years were subjects in this study. Each child came to the laboratory on three occasions. The first visit was to familiarize the child with the procedures. On the second visit, each child performed a maximal exercise test on a cycle ergometer (mean VO2. 49.5 ± 3.6 ml•kg''-min-') . On the third visit, an indwelling catheter was placed in a forearm vein. Thirty minutes later baseline blood and saliva samples were obtained followed by 30 minutes of exercise on a cycle ergometer at 69.5 ± 3.0% of VOA. Blood and saliva samples we e obtained at mid-exercise, end exercise and 15 minutes post-exercise. Serum and salivary cortisol were analyzed using RIA skit. Serum samples were corrected for changes in plasma volume. A repeated measures ANOVA revealed that exercise significantly increased serum, but not salivary cortisol. Mean salivary cortisol (ug.dl'') at baseline was 0.079 ± 0.042, at mid-exercise 0.099 ± 0.070, at end-exercise 0.133 ± 0.112, and at 15 minutes post-exercise was 0.143 ± 0.140. Post-hoc analyses indicated that mean serum cortisol at midexercise (7.94 ± 4.53 ug•dl-'), end-exercise (8.72 ± 5.61) and 15 minute post-exercise (8.21 ± 5.03 ug•dl'') were significantly greater than baseline (5.54 ± 2.73 ug•dl-'). The ratio of mean salivary to mean serum cortisol ranged from 1.3% to 1.7%. Serum and salivary cortisol were significantly correlated at mid-exercise (r=0.77), post-exercise (r=0.90) and 15 minutes post-exercise (r=0.84), but not at baseline. It is concluded that: (1) as a result -of exercise, children show adrenocortical activation as measured by serum cortisol; and, (2) salivary and serum cortisol are strongly correlated during and after exercise in children. / School of Physical Education