Objectives/Methods. Acute physical activity increases the release of reactive oxygen species (ROS). It is not yet known, what this means in the context of diseases which are accompanied by chronically increased oxidative stress levels, e.g. type 2 diabetes. For this reason, we studied ROS production (immunhistochemical analysis of 8-isoprostaglandin F2a as marker for ROS-induced lipid-peroxidations) as well as the oxidation of antioxidative proteins (peroxiredoxins, immunhistochemical analysis of peroxiredoxin-overoxidation) in erythrocytes of non-insulin-dependent type 2 diabetic men (n=9, 62±10 years, BMI: 31±4 kg/m²) during acute exercise (bicycle ergometer, WHO-test scheme until subjective exhaustion, taking blood samples before exercise, every 50 W, directly at exhaustion/test-abort and 2,4,6,10,20,30 and 60 minutes after exercise). Results: Both, 8- isoprostaglandin F2a (8-ISO) and overoxidized peroxiredoxin (Prx-SO3) concentrations increased over the time of endurance performance to exhaustion (ANOVA: p <= 0.05). To describe trends, 8-ISO concentration was 3.8-fold increased at physical exhaustion (128 ± 48 W) in comparison to basal conditions (arbitrary grey values (arGV): basal 1512 ± 1347 DU [density unit] vs. physical exhaustion 5665 ± 2690 DU). Prx-SO3 was found 3.4-fold increased (arGV: basal 3447 ± 1766 DU vs. physical exhaustion 11791 ± 7605 DU). In the recovery phase 8-ISO concentrations decreased, whereas Prx-SO3 levels did not change over time. Conclusions: Acute exercise leads to an oxidative stress response in red blood cells of type 2 diabetic men. ROS are buffered insufficiently and induce an increase in (over-)oxidation of lipids and peroxiredoxins. A 60 minute recovery period is not enough to decrease all oxidation product concentrations to normal levels.