Enhanced Fas system-mediated hepatocyte apoptosis is observed in hepatitis C virus (HCV)- and hepatitis B virus (HBV)-associated chronic liver diseases. In these forms of viral hepatitis, liver-infiltrating lymphocytes that recognize the viral antigen on hepatocytes become activated and express cytolytic Fas ligand (FasL) molecules. In contrast, hepatocytes exhibit enhanced Fas expression and become susceptible to FasL-mediated death. Augmentation of the Fas system has also been observed in other liver diseases and biliary disorders. Moreover, the Fas system is involved in removing aged hepatocytes. Thus, Fas-mediated apoptosis plays an important role in several liver diseases and in maintaining normal liver homeostasis.