The activities of antioxidant enzymes: superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSHPx), glutathione-S-transferase (GST) and glutathione reductase (GR) were examined in liver, kidney cortex and heart tissues of lambs fed diets supplemented with inorganic (sodium selenite) and an organic (Se-yeast) form of selenium. Additional selenium resulted in a significant increase of the Se content in the examined tissues in both supplemented groups. The activities of GSHPx, CAT in the liver as well as of CAT, GST and SOD in the kidney cortex were significantly lower in the Se-yeast supplemented group when compared with both the control and selenite-fed groups. In the heart, the activities of all of the assayed enzymes increased in both supplemented groups. SOD activity was found to be significantly higher in the Se-yeast supplemented group when compared with the selenite group. In addition, two Cu, Zn-SOD isoenzymes of higher band intensity were generated in this group, probably as a result of oxidative stress, which was also manifested by a significant increase of thiobarbituric acid reactive substances (TBARS). The presented results suggest specific regulation of antioxidant enzyme activities in the tissues of lambs depending on the form of selenium intake.