The relationship of oxidative stress and the anti-oxidant defence system to maximal oxygen consumption (VO2max) and habitual physical activity was assessed in 26 elderly men (71.0 +/- 4.2 years) and compared to that of 12 young men (22.1 +/- 5.1 years). Physical activity was assessed by a questionnaire. Malondialdehyde (MDA), plasma total anti-oxidant status (TAS), the levels of red blood cell (RBC) superoxide dismutase (SOD) and glutathione peroxidase (GPX), as well as serum GPX activities were determined under resting conditions. The older and young men had similar TAS and RBC SOD, while MDA, RBC GPX and plasma GPX were higher, and RBC SOD/GPX ratio was significantly lower in the older men. Neither MDA nor anti-oxidants were associated with any of the physical activity/aerobic capacity measures in the elderly men. We conclude that in healthy elderly men with a good nutritional status, indicators of the anti-oxidant defence system are not lower in comparison with young men. Increased RBC and plasma GPX coupled with a high level of lipid peroxidation marker may indicate an adaptation of anti-oxidant defences to sustained oxidative stress. Furthermore, the results of the present study suggest that the level of habitual physical activity and aerobic capacity have no major influence on the resting balance between radical generation and blood anti-oxidant potential in healthy older men.