The reversible oxidation–reduction of glutathione is important for many of its biological functions. It maintains a ratio of about 10011 of GSH to G—S—S—G. Glutathione (reduced) performs specialised functions in erythrocytes. It maintains RBC membrane structure in integrity. It protects haemoglobin from getting oxidised by agents such as H₂O₂. It involves in the transport of amino acids in the intestine and kidney tubules. Toxic amounts of peroxide and free radicals produced in the cells are scavenged by glutathione peroxidase.

It is involved in detoxification (removing toxic substances). It acts as coenzyme (PGE₂ synthase and glyoxalase). It involves in the formation of correct disulphide bonds in several proteins.