In order to analyze the participation of oxidative stress in MDS development, we examined the systemic levels of reactive oxygen and nitrogen species (peroxides and NO), antioxidant defenses (uric acid, vitamin E (plasmatic and erythrocytic), vitamin A, GSH, TAS, erythrocytic GPX and GR activities), and macromolecule oxidative damage (8-OHdG and MDA (plasmatic and erythrocytic)) between patients and controls. This evidence concerns the gene GSR and myelodysplastic syndrome.