To evaluate the role of apoptosis on liver injury of chronic hepatitis B, we studied the expression of Fas ligand and HBsAg immunohistochemically. Sixty-eight liver biopsy samples from patients with type B chronic liver disease were immunostained for Fas ligand and thirty-two of which were immunostained for HBsAg.35/68(51.47%) cases showed FasL immunoreactive in liver-infiltrating mononuclear cells, and more expression of FasL were found in cytoplasm of hepatocytes. Both were closely linked to the degree of inflammation in liver(P = 0.008 and P = 0.011, respectively). But the expression of FasL had no close relationship with that of HBsAg in liver tissue (P > 0.05). These findings suggest that apoptosis caused by CTL through Fas-mediated pathway plays an important role in liver cell injury by hepatitis B virus infection. At the same time, FasL-positive hepatocytes may express cytotoxic activity and eliminate themselves by both fratricide and suicide; 'Bystander effect' can be used to account for the difference expression between FasL and HBsAg.