Carotenoid lutein was evaluated for its antioxidant potential both in vitro and in vivo. Lutein was found to scavenge superoxide radicals, hydroxyl radicals and inhibited in vitro lipid peroxidation. Concentrations needed for 50% inhibition (IC50) were 21, 1.75 and 2.2 microg/mL respectively. It scavenged 2,2-diphenyl-1-picryl hydrazyl (IC50 35 microg/mL) and nitric oxide radicals (IC50 3.8 microg/mL) while 2,2-azobis-3-ethylbenzthiozoline-6-sulfonic acid radicals were inhibited at higher concentration. Ferric reducing power (50%) of lutein was found to be equal 0.3 micromols/mL of FeSO4.7H2O. Its oral administration inhibited superoxide generation in macrophages in vivo by 34.18, 64.32 and 70.22% at doses of 50, 100 and 250 mg/kg body weight. The oral administration of lutein in mice for 1 month significantly increased the activity of catalase, superoxide dismutase, glutathione reductase and glutathione in blood and liver while the activity of glutathione peroxidase and glutathione-S-transferase were found to be increased in the liver tissue. Implication of these results in terms of its role in reducing degenerative diseases is discussed.