Nine young (26.1 +/- 2.52 years) (M +/- SD) and seven elderly (66.0 +/- 5.85 years) untrained men performed a graded exercise to peak VO2 to compare whether serum beta-endorphin (B-EP) would respond similarly with age. B-EP levels were not different at rest (31.8 +/- 3.3 and 25.3 +/- 4.1 pg/ml in the old and young groups, respectively), and both groups displayed similar responses to exercise. Specifically, we noted no change in B-EP during the final stage of exercise followed by a significant rise for the recovery period (40.0 +/- 3.7 and 38.1 +/- 5.0 pg/ml in the aged and young groups, respectively). Post-exercise reports of anxiety and depression were unchanged in either group, and only minor changes in hostility were noted, as measured by the Multiple Affect Adjective Checklist. These results demonstrate a similar serum B-EP response in older men compared to young men following graded maximal exercise and support the contention that circulatory changes in B-EP may not be related to changes in specific affective states.