The influence of four hydroxil radical (OH•) scavengers on platelet function was investigated. OH• scavengers inhibited ADP, collagen, arachidonic acid, PAF-induced platelet aggregation, and platelet cyclooxygenase pathway activation, which was studied by evaluating platelet malondialdehyde and serum thromboxane A2 formation. The latter was not affected by superoxide dismutase, catalase, or metal ion chelants such as desferioxamine or DETAPAC. The detection of deoxyribose degradation by stimulated platelets suggested that platelets produce OH•. This study shows that activated platelets produce free radicals and that antioxidant agents such as OH• scavengers inhibit platelet f