Glutathione peroxidases(Gpxs) are ubiquitously expressed proteins which catalyze the reduction of hydrogen peroxides and organichydroperoxides by glutathione. There are several isoforms which differ in their primary structure and localization. The classical cytosolic/mitochondrial GPx1 (cGPx) is a selenium-dependent enzyme, first of the GPxfamily to be discovered. GPx2, also known as gastrointestinal GPx(GI-GPx), is an intracellular enzyme expressed only at the epithelium of the gastrointestinal tract.Extracellular plasma GPx(pGPxor GPx3) is mainly expressed by the kidney from where it is released into the blood. Phospholipid hydroperoxide GPx4 (PH-GPx) expressed in most tissues, can reduce many hydroperoxides including hydroperoxides integrated in membranes, hydroperoxylipids in low density lipoprotein orthymine. All mammalian GPx family members, except for the recently described Cys containing GPx3 and epididymis-specific secretory GPx(eGPxor GPx5)isoforms, possess selenocysteine at the active site.