Diabetes has been shown to go along with various alterations of the erythrocyte deformability. The present study investigates influence of exercise on erythrocyte deformability (EryDeform) in male patients suffering from non- insulin-dependent type 2 diabetes. EryDeform was measured in venous blood samples taken from men suffering from non-insulin dependent type 2 diabetes (n=15, age: 61±3 yrs, BMI: 30.0±1.5 kg/cm²) using the LORRCA-system (laser assisted optical rotational analyzer, Mechatronics, Netherlands) at a shear stress range from 0.3–50 Pa. Blood samples were taken before (T0), directly after (Tex) as well as 30 minutes after (Trest) a cycling ergometer testing (WHO-scheme until subjective exhaustion). The same procedure was repeated after a three months moderate endurance exercise (2x a week, 90 min). Regarding the acute influence of physical activity on shear-stress-dependent EryDeform before the onset of the training intervention, basal and maximal elongation indices measured at 0.3 Pa (EI0.3Pa) and 50 Pa (EI50PA) as well as spectrin cytoskeleton cooperativity (Hillery) were not altered, whereas shear-stress dependent sensitivity of EryDeform as measured by the pressure needed to achieve a 50% increase in EI (EC50EI) decreased at Tex and Trest (EC50EI, T0:2.99±0.56 Pa, Tex: 2.86±0.41 Pa; Trest: 2.83±0.41 Pa). Regarding longterm adaptations towards physical training under basal/not exercising conditions, we observed a decrease in EI0.3Pa (before vs. after: 0.125±0.033 vs. 0.104 vs. 0.020) and EI50Pa (before vs. after: 0.604±0.014 vs. 0.554±0.071). EC50EI and Hillery were not altered. In this situation (i.e. after a three months training intervention), exercise acutely results in a further decrease in EI50Pa (Tex: 0.545±0.069, Trest: 0.450±0.055), all other EryDeform parameters remain unaltered. Conclusion: Longterm endurance exercise seems to improve and stabilize erythrocyte deformability in men suffering from non-insulin dependent type 2 diabetes and may thus contribute to an improvement of microcirculation.