['A decrease in dopamine activity is thought to lead to a reduction in motivation and arousal and therefore to the "central" component of fatigue. The purpose of the present study was to investigate the effects of a dopamine (DA) noradrenaline (NA) reuptake inhibitor, bupropion (Zyban), on exercise performance and on the hormonal response to exercise.', 'Eight healthy well trained male cyclists (Watt(max) 397+/-15 W) participated in the study. Subjects completed one maximal exercise test (to determine maximal power output Watt(max)), and two endurance performance tests (time trials) in a double blind randomised cross-over design. Subjects took either placebo capsules (lactose) or 2 x 300 mg bupropion (BUP). Blood samples were collected for adrenocorticotropin (ACTH), prolactin, cortisol, growth hormone, beta-endorphins, and catecholamines.', 'Performance was not influenced by BUP (placebo: 89+/-1 min; BUP 2 x 300 mg: 89+/-0.7 min). All hormones increased during exercise in all trials. Cortisol plasma concentrations were significantly higher in the BUP trial at rest, at min 60, and at the end of exercise, while beta-endorphins were higher in the BUP trial at the end of exercise and during recovery, and ACTH at the end of exercise.'] Are hormonal responses during prolonged exercise influenced by a selective DA/NA reuptake inhibitor?