One hundred liver specimens of hepatitis B surface antigen positive cases were used for this study. The localization of hepatitis B core antigen in the bile duct epithelia was investigated by immunoperoxidase method. In three cases, hepatitis B core antigen was detected not only in the nuclei of the bile duct epithelia, but also in the cytoplasms of the bile duct epithelia. These findings suggested that hepatitis B virus may replicate in the bile duct epithelia. The resons for distribution of hepatitis B core antigen in the nuclei of the bile ducts are not known. A possible explanation may be that intrahepatic bile ducts develop from hepatocytes. To the best of our knowledge, morphologic localization of hepatitis B core antigen in the nuclei of the bile duct epithelia has not been reported previously