This study was aimed at investigating oxidative stress in thalassemic patients by measurement of the oxidative damage biomarker, F(2)-isoprostanes (F(2)-IsoPs), using gas chromatography-mass spectrometry. The results showed that the mean value of urinary F(2)-IsoPs, normalized with creatinine, in the thalassemic group was significantly higher than that from healthy subjects (3.38+/-2.15 ng/mg creatinine vs 0.86+/-0.55 ng/mg creatinine, respectively), and the mean value of plasma total F(2)-IsoPs in the thalassemic group was also significantly higher than that from healthy subjects (0.39+/-0.15 ng/ml vs 0.18+/-0.03 ng/ml, respectively). Serum ferritin, erythrocyte superoxide dismutase (SOD), glutathione peroxidase, glutathione, and TBARS levels after treatment of erythrocytes with H(2)O(2) were also investigated, and serum ferritin and erythrocyte SOD levels were significantly higher in thalassemic patients. Our findings are consistent with oxidative stress in thalassemia patients.