To study the expression of FasL mRNA in liver tissues of CHB, we investigated FasL mRNA by in situ hybridization in liver tissues from patients with chronic hepatitis B. FasL oligonucleotide probes were synthesized and labeled with DIG-Oligonucleotide 3'-End Labeling Kit. FasL mRNA was found in cytoplasm of liver-infiltrating mononuclear cells, hepatocytes and some sinus cells. FasL mRNA-positive hepatocytes were present mainly at the edges of 'piecemeal necrosis(PN)' and 'bridging necrosis (BN)'. These results demonstrated that human hepatocytes themselves can express FasL in chronic hepatitis B. We deem that FasL-positive hepatocytes might express cytotoxic activity and eliminate Fas-positive hepatocytes by both 'fratricide' and 'suicide'. These results also emphasize that apoptosis caused by CTL through Fas-mediated pathway may play an important role in CHB.