The extent of platelet activation after exhaustive exercise remains under discussion. Previous studies have provided contrary data, probably due to differences in the methodologies and the enrolled subjects. In the present study a maximal treadmill exercise (TR) was used to test platelet activity and -reactivity in 13 healthy non-smoking men. Blood samples were taken after a 30min rest, immediately before and after exercise, and 1h after completion of exercise. Platelets were analysed by whole blood flow cytometry either directly or after in vitro stimulation by incubating the blood samples for 10min with TRAP-6 (10µM) or ADP (5µM or 2,5µM). Binding of an anti-CD62P antibody or a PAC1 antibody directed against the activated fibrinogen receptor GPIIb/IIIa were used as a measure of platelet activation. Immediately after TR the percent CD62P positive platelets (%PC) unstimulated increased (p<0.01) from 0.77±0.06 to 1.12± 0.09 %PC and in PAC1 (p<0.05) from 2.32 ±0.54 to 3.83±0.81 %PC (mean±SEM). After ADP-stimulation an increase from 4.18±1.02 to 5.69±1.40 %PC in CD62P (p<0.01) and from 45.7±3.4 to 57.9±6.6 %PC in PAC1 (p<0.05) after TR were detected. Using TRAP-6-stimulation only the increase of PAC1 (p<0.01) after TR was different in comparison with the control experiment without exercise. Soluble CD62P in plasma as a marker of platelet and endothelial cell activation was also enhanced (p<0.05) after TR. Although these results indicate that exhaustive exercise lead to a small platelet activation and an increase in platelet reactivity, it is rather doubtful that these changes alone implicate a prothrombotic situation in healthy young non-smokers.