Platelet-dependent thrombus formation may be influenced by alteration of platelet or vascular redox state, the presence of endogenous or exogenous antioxidants, as well as the formation of reactive oxygen and nitrogen species. Specifically, settings and pathways that influence the formation of superoxide and nitric oxide, as well as their metabolism, may influence platelet function and thrombus formation. Although some antioxidant regimens have been associated with bleeding and hemorrhagic stroke, the therapeutic value of antioxidants in clinical syndromes that lead to platelet-dependent thrombosis is not clear, as supplemental antioxidants have not been generally associated with better cardiovascular outcome.