Wistar male and female rats were exposed to ethylene oxide (EO) at a concentration of 250 ppm, 6 hours a day, 5 days a week for 17 weeks simultaneously, and the effects of EO on the glutathione metabolism and lipid peroxidation in the liver in regards to sexual difference were studied. Although the liver weight of the male exposed group did not alter, that of the female exposed group increased when compared with the control group. This increase was not accompanied with the alteration of protein content per gram of liver in the cytosol fraction and total homogenate. Among the glutathione related enzymes in the liver, the glutathione reductase activity of both male and female exposed groups decreased compared with each control group, and there was no difference in the degree of the decrease. The glutathione peroxidase activity increased only in the male exposed group. The glutathione-S-transferase activity of both male and female exposed groups increased significantly. In the male exposed group, the activity increased greater than that in the female exposed group. In the male exposed group, the lipid peroxide level in the liver increased slightly but not significantly.