Acute physical exercise stimulates the activity of the hypothalamus-pituitary-adrenal axis in man. In the present study we measured plasma adrenocorticotropin, beta-endorphin, beta-lipotropin and cortisol levels in 27 male trained athletes in basal conditions, 60 min before and immediately after an official competition. The endocrine responses were evaluated in different groups of athletes participating in races (100 m, 1500 m, 10,000 m) or in the disc throw. The athletes competing for the runs showed a statistically significant increase in plasma adrenocorticotropin, beta-endorphin, beta-lipotropin and cortisol levels after the race (P less than 0.01), whereas the disc throwers showed no significant change in the hypothalamus-pituitary-adrenal axis hormones after the competition. The percent increase in plasma adrenocorticotropin, beta-endorphin, beta-lipotropin and cortisol was higher in the athletes who run 1500 m and 10,000 m than in those participating in the short distance race (100 m). The present results showed that plasma proopiomelanocortin-related peptides and cortisol levels increase in trained athletes following running competition and that this increase is related to the duration of the physical exercise.