It is documented that hyperhomocysteinemia (HHcy) is an independent risk factor for atherosclerosis, but whether elevated plasma homocysteine contributes to the progression of atherosclerosis in aged animals with hypercholesterolemia is still unknown. HHcy was induced in apolipoprotein E (ApoE) knockout mice (male, 32 weeks old) by feeding 2% methionine/low folate (1 mg/kg) diet for 20 weeks. HHcy induced by methionine feeding significantly increased oxidative stress, as measured by thiobarbituric-reactive substances in livers (P < .05) and genetic expression of Cu,Zn-superoxide dismutase, in methionine-fed animals compared with controls (P < .05). Furthermore, lipoprotein profiles were changed, in that low-density lipoprotein-cholesterol was shifted to very low-density lipoprotein in the methionine-supplemented group. However, nuclear factor kappaB activity, atherosclerotic lesions, hepatic glutathione level, lipid profiles, and activities of aspartate aminotransferase and alanine aminotransferase were not significantly different. These findings suggest that HHcy induced by methionine may promote disturbances in lipid peroxidation and modify lipoprotein metabolism but not contribute to the progression of atherosclerotic lesion in aged ApoE knockout mice.