An increase in plasma beta-endorphin concentrations during exercise has been reported in adult men and women by several investigators. However, very little is known about this physiological hormonal response to exercise in children. In this study, we investigated plasma beta-endorphin, ACTH and GH responses to exercise in 40 prepubertal and pubertal children. Subjects were recruited as part of a population of children and adolescents presenting growth retardation and were selected on the basis of the absence of any clinical or biological signs of endocrine or metabolic disease. There were 16 girls and 24 boys with 24 prepubertal and 16 pubertal individuals. A standardised 15 min workload on cycloergometer was used to progressively increase the heart rate of the children up to 90% of the theoretical maximal value. Exercise resulted in a significant increase (p < 0.01) in plasma beta-endorphin (mean +/- SEM) (4.26 +/- 0.47 vs 5.74 +/- 0.56 fmol/ml), ACTH (3.71 +/- 0.41 vs 6.2 +/- 0.62 fmol/ml) and GH (147 +/- 29 vs 364 +/- 67 fmol/ml). The percentage of children with significant hormonal response to exercise was about 75% for each of the 3 hormones but only 3 of the 40 children studied did not show any hormonal response to exercise. Exercise-induced increases in plasma beta-endorphin and ACTH were significantly correlated (p < 0.01). By contrast, there was no significant relationship between GH and beta-endorphin or ACTH values. Furthermore, whereas exercise-induced plasma GH increase was significantly higher in pubertal than in prepubertal children (p < 0.001), corresponding beta-endorphin and ACTH levels were quite similar in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)