Effects of aging and hypercholesterolemic diet on lipid peroxidation and antioxidant status were investigated in rats. The rats were divided into four groups of ten: Group I; young rats receiving standard lab chow; Group II; young rats on hypercholesterolemic diet (0.4 g/rat/day); Group III; aged rats receiving standard lab chow; Group IV; aged rats on hypercholesterolemic diet (0.4 g/rat/day). Plasma lipid peroxidation end product level was determined as thiobarbutiric acid reactive substances (TEARS). Plasma cholesterol concentration was analyzed by a kinetic enzymatic method. Erythyocyte superoxide dismutase (CuZn SOD), glutathione peroxidase (GSH Pr) and glutathione (GSH) levels were determined spectrophotometrically. Cholesterol values were found to be significantly high (p < 0.001), TEARS (0.05 > p > 0.02) and GSH (p < 0.001) levels significantly low in aged rats in comparison with young rats. Hypercholesterolemic diet induced significant increases in GSH (p < 0.001) and CuZn SOD (p < 0.001) levels, whereas a significant decrease in GSH Pr activity (0.05 > p > 0.02) was observed in aged rats. In young rats hyperchlesterolemic diet caused a significant increase in both GSH and CuZnSOD levels. Our results indicate an imbalance between radical production and destruction in favour of prooxidant conditions in the young rats and the induction by hypercholesterolemic diet of the antioxidative response in erythrocytes. (C) 1997 Elsevier Science B.V.