The goal of this study was to assess if oxidative stress, as measured by alterations in the concentrations of antioxidant enzymes in the liver and erythrocytes of cattle, could be induced following dl-ethionine administration. Whole blood, serum and liver biopsy samples were collected 0, 4, 7 and 10 days after intra-peritoneal ethionine administration to five cows. The activities of the antioxidant enzymes copper zinc superoxide dismutase (Cu, Zn SOD) and catalase were assessed in the liver biopsies which were also examined histopathologically. Significant increases in hepatic Cu, Zn SOD concentrations (P<0.01) were noted on days 7 and 10 post-treatment. Hepatic catalase activity decreased significantly (P<0.01) on days 4, 7 and 10 post-treatment and erythrocyte Cu, Zn SOD activity was significantly increased on day 10. Serum biochemical analysis revealed a significant increase (P<0.01) in non-esterified fatty acid concentrations on day 4 and significant decreases in total cholesterol and phospholipid levels on days 4 (P<0.05), 7 (P<0.01) and 10 (P<0.01). In this model system, dl-ethionine administration was effective in inducing oxidative stress particularly reflected in the liver