Objective: Platelet activation and thrombus formation tendency increase in diabetes mellitus. Nitric oxide (NO) synthesized by platelets plays important role in platelet functions and limits the recruitment of new platelets to the platelet-rich thrombus. However, NO may also be deleterious by elevating oxidative/nitrosative stress in cells. The aim of the present study was to examine effects of acute high glucose in both resting and collagen-stimulated platelets on platelet aggregation, oxidative stress and NO bioavailability. In addition, we investigated the role of superoxide production on NO bioavailability using quercetin as scavengers of superoxide anion.