The effects of methyl mercuric chloride (CH3 HgCl) and mercuric chloride (HgCl2) on red blood cell (RBC), plasma, and liver glutathione peroxidase (GSH-Px) activities were determined in Japanese quail fed a semipurified diet with 1 ppm added selenium (Se). The RBC GSH-Px activity was significantly increased by 5 ppm mercury (Hg) as CH3 HgCl. Plasma GSH-Px activity was significantly depressed only in th 20 ppm Hg group. Liver GSH-Px activity was not affected. The RBC GSH-Px activity was significantly lower at all levels of HgCl2 compared to the Ch3 HgCl-treated birds. Plasma and liver GSH-Px activity of the HgCl2 -treated birds were not significantly different from control values. In a second experiment, GSH-Px activity and estimates of peroxidation via the thiobarbituric acid (TBA) test were determined on quail fed diets containing . 07 ppm added Se to which either 10 ppm Hg as CH3 HgCl or 150 ppm Hg as HgCl2 were added with or without the supplementation of vitamin E. Plasma and kidney GSH-Px activities were unaffected by CH3 HgCl, whereas RBC GSH-Px was significantly elevated. Kidney GSH-Px was significantly depressed by HgCl2-Vitamin E had no effect on GSH-Px activities. Vitamin E protected the liver, kidney, and brain from peroxidation; however, peroxidation was not induced by either of the mercurials VSports手机版. .