Oxidative stress is involved in the pathogenesis of acute ischemic stroke. Antioxidants are consumed in the reaction with free radicals generated during the oxidative stress. The aim of the study was the to evaluate the oxidative stress in patients with acute ischemic stroke. Malondialdehyde (MDA), plasma glutathione, plasma glutathione peroxidase (GPX), catalase (CAT), uric acid, bilirubin, plasma superoxide dismutase (SOD), red blood cells superoxide dismutase (RBS SOD) (spectrophotometric assay), total antioxidant capacity (TAC) (enhanced chemiluminescence), ceruloplasmin, C-reactive protein (CRP), albumin, transferrin (nephelometric assay) were performed in 57 patients (mean age 73.4 +/- 6.5 years) with acute ischemic stroke within 24 hours and at 7 days after stroke onset as compared to 51 age-and sex-matched controls. Significantly lower values in the first 24 hours were: plasma glutathione, CAT, plasma SOD, RBS SOD (p < 0.001), plasma GPX, TAC, transferrin (p < 0.05). Significantly higher values in the first 24 hours were: CRP (p < 0.001), MDA, uric acid (p < 0.05). Significantly lower values at 7 days were: TAC, albumin, transferrin (p < 0.001), plasma glutathione, plasma SOD, CAT (p < 0.05). Significantly higher values at 7 days were: MDA, plasma GPX, RBC SOD, CRP, uric acid, bilirubin (p < 0.001), ceruloplasmin (p < 0.05). These results indicate that oxidative stress is increased and that the majority of antioxidants are reduced; this suggests the possibility of therapeutic intervention with antioxidant agents.