1. Female and male adult mouse and rat liver was analyzed for glutathione peroxidase activity, mRNA levels, and other selected liver enzymes. 2. Species and sex differences in liver protein, total RNA and total mRNA were minor. 3. Glutathione peroxidase activity, mRNA levels, and selenium concentration was lower in male rats when compared to female rats, male mice or female mice. 4. Plasma ceruloplasmin activity, but not liver mRNA levels, were lower in mice compared to rats. 5. Cu,Zn-superoxide dismutase activity and mRNA were not greatly influenced by species or sex. 6. Glutathione transferase activity towards 1-chloro-2,4-dinitrobenzene was highest in male mice and equivalent in the other three groups.