The expression and activity of selenoenzymes are regulated by Se. In the present study, the effects of different forms and concentrations of Se on the regulation of glutathione peroxidase (GPx) activity and phospholipid hydroperoxide GPx (GPx4) and type I deiodinase (D1) mRNA levels in chicken hepatocytes were evaluated. Primary cultured chicken hepatocyte monolayers derived from male White Leghorn chickens (aged 30-40 d) were incubated for 24 h with 0 (control), 0.5, 1, 1.5, 2, 3, 4 or 5 μmol/l of Se supplied as dl-selenomethionine (Se-Met), κ-selenocarrageenan (Se-Car) or sodium selenite (Na2SeO3). Compared with the control, Se significantly increased GPx activity in all the hepatocytes, but the activity was not increased in the hepatocytes treated with 5 μmol/l of Na2SeO3, with maximal effects being observed at 2 μmol/l of Se-Met or Se-Car and at 1.5 μmol/l of Na2SeO3, respectively. Significant decreases in GPx4 mRNA levels were observed in all the hepatocytes treated with Se (v. control). The D1 mRNA levels were significantly increased in all the groups treated with Se (v. control), with maximal effects being observed at 1.5 μmol/l of Se-Met and at 0.5 μmol/l of Se-Car or Na2SeO3, respectively. Se-Met at doses of 1.5-5 μmol/l had a greater effect on D1 mRNA than Se-Car and Na2SeO3 at equivalent doses. After resulting in a maximal effect, higher Se supplementation led to a dose-dependent reduction in GPx activity and D1 mRNA levels in all the hepatocytes treated with Se. These results suggest that in chicken hepatocytes, the regulations of GPx and D1 by different forms and concentrations of Se vary.