The hypothesis that calcium provoke O₂^- formation by Kupffer cells and may contribute to carbon tetrachloride (CCl₄) induced liver injury was studied in SD rats. In CCl₄-treated animals, hepatic malonaldehyde (nmole/gm liver) and plasma ALT (IU/ml) levels elevated significantly from 119.63 ± 13.00 to 268.97 ± 14.82 and from 17.3 ± 0.18 to 806.08 ± 37.63, respectively, compared to those in controls. Activation of Kupffer cells with high dose of retinol (250,000 IU/kg/day, po, for 7 day) significantly enhanced ALT levels, while inactivation of Kupffer cells with gadolinium chloride (7.5 mg/kg/day, ip, for 2 day) attenuated the increase of serum ALT level following CCl₄ treatment. Diltiazem (10 mg/kg/day, ip for 2 day) given in combination with retinol led to a marked decrease in ALT levels compare to the level in rats treated only with retinol against CCl₄ treatment. In order to determine any alterations in cytochrome P450 activities, the P450 content and the CYP2E1 activity were measured and all CCl₄-treated rats showed significantly lower levels compared to those in controls and vehicle-treated animals. There were significant increases in glutathione peroxidase in all CCl₄-treated rats except diltiazem treated groups. No difference was found among untreated and vehicle-treated rats. It is concluded that Kupffer cells contribute to CCl₄-induced liver injury and that calcium antagonist attenuated the increased CCl₄-induced liver injury due to activation of Kupffer cells.