Abstract. A chronobiological study was carried out in seven elderly male subjects (78–84 years) to evaluate the 24-h beta-endorphin secretory pattern. Seven young adult males (28–37 years) made up the control group. Blood samples were drawn every four hours from 08.00 to 20.00 h and every two hours from 24.00 to 06.00 h. ACTH and cortisol levels were also determined in the same plasma samples. Mean 24-h beta-endorphin values in the elderly (32.6 ± 1.1 ng/l) and in the young adult male subjects (29.5 ± 1.4 ng/l) did not differ statistically, but the circadian rhythm was absent in the elderly subjects. In the elderly, plasma ACTH and cortisol concentrations showed a circadian rhythm similar to that observed in the adult subjects. However, in the elderly patients, in contrast to that in the adult subjects, the multilinear regression analysis did not show any statistically significant correlation between the beta-endorphin, ACTH and cortisol 24-h plasma concentrations.