Experiments were conducted with rats to determine if administration of excess selenium (Se) alters hepatic glutathione (GSH) metabolism. Se was fed, 6 ppm as Na2SeO3, for 6 weeks in a 15% casein, tocopherol-free diet and compared to 0.1 ppm Se. High Se significantly increased the concentrations of hepatic nonprotein sulfhydryls (NPSH) and oxidized glutathione (GSSG) as well as the GSSG:NPSH ratio. Of the NPSH, 94.1 +/- 1.7% was shown to be GSH. Similar increases in NPSH, GSSG and GSSG:NPSH due to high Se were seen when the diet was supplemented with methionine (0.3%) and/or vitamin E (100 IU/kg diet) although methionine independently increased NPSH and GSSG. Hepatic glucose-6-P dehydrogenase, glutathione reductase and gamma-glutamyl-transpeptidase activities were significantly increased by high Se but cysteine dioxygenase activity was unaffected. An i.p. injection of Na2SeO3 (15 mumol Se/kg body weight) significantly increased hepatic GSSG, which was followed by an increase in NPSH(GSH) compared to saline controls. These results indicate that excess Se causes a shift in hepatic GSH toward a more oxidized state. Increases in NPSH(GSH) and in the enzyme activities observed appeared to be adaptive changes initiated in an attempt to maintain a normal GSSG:GSH ratio. Elevated GSSG or the increased GSSG:GSH ratio caused by Se may initiate these adaptations.