Although we did not observe any O2-dependent changes in Hb-SSG levels in our study, this source of GSH is there in RBCs and most likely may be used under harsh conditions such as smoking and disease (chronic renal failure, iron deficiency anemia, hyperlipidemia, diabetes mellitus, Friedreich's ataxia, atherosclerosis). This evidence concerns the gene GSTM1 and chronic kidney disease.