The preventive effect of KZ-1026 on acute liver injury induced by CCl4 in rats was evaluated histochemically, enzyme-histochemically and ultrastructurally. Rats that received 50% CCl4 (2 ml/kg) intraperitoneally were sacrificed at 3, 7 and 24 hr. Remarkable reductions in hepatic glycogen, RNA and G-6-Pase activity were observed in the centrilobular area at 3 hr, and ballooned cells appeared in the mid-zone at 7 hr. At 24 hr, the above histochemical parameters in the hepatocytes of the centrilobular area and mid-zone were extensively reduced, while the number of ballooned cells in the mid-zone was increased. KZ-1026 (200 mg/kg) was given orally at 24 and 4 hr before, simultaneously with or 3 hr after CCl4 treatment, and each rat was sacrificed at 24 hr after CCl4 administration. Pretreatment with KZ-1026 24 hr before CCl4 administration prevented reduction of RNA, glycogen and G-6-Phase activity, as well as disruption of rER and proliferation of sER due to CCL4 toxicity. This preventive effect of KZ-1026 was reduced by posttreatment; however, only the decrease in cytoplasmic RNA was well prevented. These results suggested that KZ-1026 is protective against CCl4-induced acute liver injury.