Multiple lines of evidence suggest a role for endogenous lipopolysaccharides in toxin-induced liver injury. Toll-like receptor 4 has recently been implicated as a cell surface receptor important for lipopolysaccharide responsiveness. In these experiments, we sought to determine the role of toll-like receptor 4 in acute liver injury by carbon tetrachloride by utilizing the naturally occurring toll-like receptor 4 mutant and wild-type mice strains. Mice were injected with either carbon tetrachloride or the carrier. Serum transaminase levels peaked at 24 hr after carbon tetrachloride administration for both wild-type and mutant mice, with no significant histological difference in initial liver injury between the two groups. However, an overall decrease in hepatocyte proliferation was found in the mutant mice. Examination of the liver tissue revealed significant decreases in intrahepatic expressions of proinflammatory mediators. In conclusion, our results suggest that toll-like receptor 4 is important in the hepatic regenerative response to CCl4 liver injury via its role in modulating the inflammatory response to hepatic injury.