Exercise has been noted in some, but not all, studies to elicit an oxidative stress. The discrepancy in findings may be related to differences in exercise intensity across protocols, as well as to differences in training status of participants. OBJECTIVE We compared blood oxidative stress biomarkers in exercise-trained men after three different bouts of exercise of varying intensity and duration, as well as a nonexercise condition. METHODS On different days, men (n = 12, 21-35 yr) performed aerobic cycle exercise (60 min at 70% HR reserve) and cycle sprints (five 60-s sprints at 100% maximum wattage obtained during graded exercise testing and ten 15-s sprints at 200% maximum wattage obtained during graded exercise testing). Blood was collected before and 0, 30, and 60 min after exercise and analyzed for malondialdehyde, hydrogen peroxide (H(2)O(2)), advanced oxidation protein products, and nitrate/nitrite (NO(x)). As indicators of antioxidant status, Trolox equivalent antioxidant capacity, superoxide dismutase, catalase, and glutathione peroxidase were measured. RESULTS No differences were noted in malondialdehyde, H(2)O(2), advanced oxidation protein product, or NO(x) between conditions or across time (P > 0.05). Antioxidant capacity was generally highest at 30 and 60 min after exercise and lowest at 0 min after exercise. CONCLUSIONS In trained men, and considering the limitations of the current design (e.g., inclusion of selected oxidative stress and antioxidant biomarkers measured in blood only), strenuous bouts of exercise do not result in a significant increase in blood oxidative stress during the 1-h postexercise period. These findings may be related to attenuation in reactive oxygen species production as an adaptation to chronic exercise training and/or a protective effect of the antioxidant system in response to acute strenuous exercise.