The purpose of this study is to examine plasma cortisol and adrenocorticotropin (ACTH) levels following a brief high-intensity bout of exercise. Each subject (n = 6) performed a 1-min bout of exercise on a cycle ergometer at 120% of his maximum O2 uptake. Blood samples were collected at rest, immediately following the exercise bout, and at 5, 15, and 30 min postexercise. Mean (+/- SE) plasma ACTH levels increased significantly (P less than 0.05) from 2.2 +/- 0.4 pmol/l at rest to 6.2 +/- 1.7 pmol/l immediately following exercise. Mean (+/- SE) plasma cortisol levels increased significantly from 0.40 +/- 0.04 mumol/l at rest to 0.52 +/- 0.04 mumol/l at 15 min postexercise. These data show that brief high-intensity exercise results in significant increases in plasma cortisol and ACTH levels. Furthermore, the temporal sequence between the two hormones suggests that the increase in plasma cortisol levels following brief high-intensity exercise is the result of ACTH-induced steroidogenesis in the adrenal cortex.