Oxidative stress and antioxidative capacity of platelets and the relationship with thrombocytopenia were determined in patients with vivax malaria and compared with those of healthy subjects. Whole blood thrombocyte count, platelet superoxide dismutase and glutathione peroxidase activities of patients with vivax malaria were lower and platelet lipid peroxidation levels were higher in patients than those of healthy subjects. There was an important negative correlation between whole blood thrombocyte count and platelet lipid peroxidation level. The antioxidative mechanisms of thrombocytes were insufficient in malaria patients and caused oxidative stress. The oxidative damage of thrombocytes might be important in the ethiopathogenesis of thrombocytopenia occurring in malaria.