Hepatitis B virus (HBV) DNA and viral antigens were simultaneously identified by immunohistochemical staining of formalinfixed, paraffin-embedded liver sections followed by in situ hybridisation. In the developed radioautographs, silver grains indicate the location of viral DNA in the cell and the immunohistochemical stain marks sites of accumulation of viral antigen. In liver from a patient with chronic active hepatitis serologically positive for hepatitis B surface antigen and e antigen (HBsAg/HBeAg) viral nucleotide sequences, representing actively replicating DNA species, were demonstrated predominantly in the cytoplasm. Viral core antigen (HBcAg) was expressed in the liver cell nuclei. HBcAg was not detectable in most hepatocytes with high levels of viral replication. Conversely, most liver cells in which HBcAg was found did not contain replicating HBV. HBcAg and replicating viral DNA species were not detectable in hepatocytes undergoing pathological changes, such as ground glass cells. Because no pathological changes could be identified either in hepatocytes with high levels of HBV replication or expression of nuclear HBcAg, the liver cell damage in this patient with chronic hepatitis B was presumably induced by other mechanisms. The simultaneous observation of viral DNA, antigens, and pathological changes at the single cell level and their correlation with clinical findings should contribute to the understanding of the molecular mechanisms underlying HBV-induced liver cell injury.