Glycated hemoglobin can be degraded by proteolytic enzyme(s) in the erythrocyte. The enzyme(s) co-elutes with glycated hemoglobin when the latter is separated from erythrocyte lysates using the cation-exchanger Bio Rex-70. A further purification of the Bio Rex eluant on DEAE Sephadex A-50 separated the enzyme(s) from glycated hemoglobin. Studies with the Bio Rex eluant showed that degradation of glycated hemoglobin is maximum at 37 degrees C at pH 8.6. Proteolytic degradation is inhibited by 5 mM N-ethylmaleimide (NEM), 5 mM ethylenediamine tetraacetic acid (EDTA) and 0.6 mM n-p-tosyl-L-lysine choromethyl ketone (TLCK) (100-87 and 76% inhibition respectively). This study also examines the possibility that oxidative-damage to glycated hemoglobin increases its susceptibility to proteolytic degradation. When incubated with various anti-oxidants like DTPA, uric acid, mannitol and butylated hydroxy toluene (BHT), proteolytic degradation of glycated hemoglobin decreased by 66.1, 50.7 and 38% respectively.