The effects of feed supplementation with anorganic and organic forms of Se on the activities of liver enzymes, glutathione peroxidase (cGPx) and superoxide dismutase (SOD), was examined in young growing chickens. The birds were divided to 4 groups on the day of hatching. The first group received the basic diet (BD) with a Se content 0.12 mg·kg^-1of dry matter (DM) only. Diets for groups 2, 3 and 4 consisted of BD supplemented with sodium selenite, 0.2 mg·kg^-1 of DM; Se-enriched yeast, 0.2 and 0.7 mg·kg^-1 of DM, respectively. Analysis of the liver tissue from 2- and 4-week-old chickens showed no effects of the various Se intake or effects of the form supplemented to the diet on cGPx activity. The 2-week-old birds showed no significant effects of diets on SOD activity in the liver tissue. On the other hand, liver SOD activity appeared to be dose-dependent in 4-week-old chickens, but no effects of the form of Se applied were found. Lipid peroxide formation measured as the appearance of thiobarbituric acid-reactive substances (TBARS) showed no dependence on the amount or form of Se supplemented to the ration, but its content in the liver of 4-week-old chickens was higher than in the 2-week-old ones. The selenium level in the liver tissue was clearly related to its contents in the feeds, but no effects of the form of selenium supplemented on this parameter were noticed after 2 or 4 weeks of dietary intake. The presented results suggest that dietary supplementation with Se-yeast to a level reaching even 0.7 mg·kg^-1 of DM does not induce oxidative stress in young growing chickens. The synthesis of liver cGPx of 2- to 4- week-old chickens of a laying strain already seemed to be saturated at a dietary intake of Se at a level of 0.1 mg·kg^-1 of DM.