A study with four groups, each with 9 individually-housed, male albino rats (clinical average weight = 65 g), was undertaken to examine the effect of increasing dietary iron levels on the oxidant status in liver and colon of growing rats. The basal maize/soya diet contained 70 mg iron per kg and was supplemented with 200 (group II), 500 (group III) and 2000 (group IV) mg Fe/kg from iron (II) fumarate. Liver-Fe was closely correlated (r = 0.997) with dietary Fe intake. Feeding diets supplemented with 500 and 2000 mg Fe/kg over 28 days resulted in significantly elevated TBA-RS in liver homogenates. Vitamin E in the liver was about 20% lower in group IV compared to the controls. Liver SOD, G6PDH and CAT activities were not influenced by dietary iron, whereas liver GSHPx was decreased in groups III and IV. TBA-RS in the colon mucosa significantly increased only at a dietary iron supply of 2000 mg per kg. Iron-enriched diets caused a moderate dose-dependent enhancement in the concentration of methane sulfinic acid in feces samples, which was formed by the reaction of hydroxyl radicals and dimethyl sulfoxide. Liver was more sensitive than the colon mucosa to iron-induced lipid peroxidation. Compared with the recommended iron requirements of growing rats very high dietary iron levels were necessary to induce oxidative stress.