Pretreatment of rats with colchicine (10 micrograms/day) for 7 days protected against CCl4-induced acute liver damage. CCl4 intoxication was demonstrated histologically and by increased serum activities of glutamic-pyruvic transaminase, alkaline phosphatase and gamma-glutamyl transpeptidase. Furthermore, an increase in liver lipid peroxidation and a decrease in plasma membrane gamma-glutamyl transpeptidase activity were found. Colchicine increased the LD50 of CCl4 2.5-fold and prevented the release of intracellular enzymes, as well as the decrease in gamma-glutamyl transpeptidase activity in the plasma membrane. It also completely prevented the lipid peroxidation produced by CCl4 and limited the extent of the histological changes. Our results suggest that the protective effect of colchicine may be mediated through its action on an early toxic event, because treatment of the animals with colchicine produced a significant decrease in CCl4-induced lipid peroxidation.