The effect of pretreatment with vitamin E on membrane lipid alterations produced by the acute intoxication with CCl4 was studied. Rats were treated with an oral dose of CCl4 (0.4 g per 100 g body weight) and 24 h later the animals were sacrificed and liver plasma membranes isolated. After extraction, the membrane lipids were analysed by thin-layer chromatography and quantitated by densitometry. The phospholipid: protein ratio determined in plasma membranes of CCl4-treated rats was almost three-fold higher than that found in control animals. Sphingomyelin (Sph) and phospharidyl choline (PC) increased, while phosphatidyl ethanolamine (PE) decreased in the plasma membranes isolated from the CCl4-treated group. Animals pretreated for 7 days with a daily dose of vitamin E (200 IU per kg body weight) showed a lower increase in the phospholipid: protein ratio (two-fold) and the changes in Sph, PC and PE were lower. When the rats were pretreated with a higher dose of vitamin E (400 IU per kg body weight) for the same period, the lipid composition of plasma membrane was normal. These results indicate that vitamin E can protect against the alterations induced by CCl4 on the liver membranes. The protective action of vitamin E against CCl4 membrane damage is probably associated with its antioxidant properties.