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Tumor necrosis factor (TNF)-α and Fas ligand (FasL) are trimeric proteins that induce apoptosis through similar caspase-dependent pathways. Hepatocytes are particularly sensitive to inflammation-induced programmed cell death, although the contribution of TNF-α and/or FasL to this injury response is still unclear. Here, we report that d-galactosamine and lipopolysaccharide-induced liver injury in C57BL/6 mice is associated with increased hepatic expression of both TNF-α and FasL mRNA. Pretreatment of mice with a TNF-binding protein improved survival, reduced plasma aspartate aminotransferase concentrations, and attenuated the apoptotic liver injury, as determined histologically and by in situ 3′ OH end labeling of fragmented nuclear DNA. In contrast, pretreatment of mice with a murine-soluble Fas fusion protein (Fasfp) had only minimal effect on survival, and apoptotic liver injury was either unaffected or exacerbated depending on the dose of Fasfp employed. Similarly, mice with a spontaneous mutation in FasL (B6Smn.C3H- Faslgldderived from C57BL/6) were equally sensitive tod-galactosamine/lipopolysaccharide-induced shock. We conclude that the shock and apoptotic liver injury afterd-galactosamine/lipopolysaccharide treatment are due primarily to TNF-α release, whereas increased FasL expression appears to contribute little to the mortality and hepatic injury.