The effects of maximal performance capacity and different work load intensities on the response of free and sulfate-conjugated plasma catecholamines, prolactin (PRL), and cortisol were studied in six healthy male volunteers. In a first experiment, the volunteers had to perform a step-wise incremental bicycle ergometer test to determine the onset of blood lactate accumulation (OBLA) and aerobic capacity (V??O2max). The levels of free noradrenaline (NE), adrenaline (Epi), and dopamine (DA) increased considerably, whereas no significant changes for sulfate-conjugated catecholamines, PRL, and cortisol were observed. In a second series of experiments with the same volunteers, the effects of 30 min exercise were studied at a constant work load intensity on 3 different days. Three intensities were used for each of the volunteers: 45%, 60%, and 75% of their aerobic capacity (i.e., below, close to, and above their OBLA). The values obtained for all parameters showed an intensity-dependent rise. The most important changes occurred at work load intensities above the OBLA. At the highest intensity, all parameters except sulfate-conjugated Ne and cortisol showed a significant increase. Although the physiologic parameters reached a steady state during exercise, there were no indications that this was the case with the values of the neuroendocrine parameters. Ten minutes after the exercise, the levels of the free catecholamines had declined considerably, whereas the values of the other parameters were unchanged or showed a further increase. Chemicals/CAS: adrenalin, 51-43-4, 55-31-2, 6912-68-1; hydrocortisone, 50-23-7; noradrenalin, 1407-84-7, 51-41-2; prolactin, 12585-34-1, 50647-00-2, 9002-62-4; Catecholamines; Dopamine, 51-61-6; Epinephrine, 51-43-4; Hydrocortisone, 50-23-7; Lactates; Lactic Acid, 50-21-5; Norepinephrine, 51-41-2; Prolactin, 9002-62-4; Sulfates.