The present study aimed to assess the endogenous antioxidant defense system in patients with MDS at diagnosis, without having received any drug therapy or following a specific diet, by measuring redox biomarkers [GSH, catalase (CAT) activity, total antioxidant capacity (TAC) and levels of lipid peroxidation through thiobarbituric acid reactive substances (TBARS) and protein (carbonyl) oxidation. Here, CAT is linked to myelodysplastic syndrome.