ABSTRACT— The expression of intercellular adhesion molecule-1 (ICAM-1) on the hepatocyte membrane was studied in 27 patients with chronic hepatitis B and C (CHB, CHC) by immunostaining using a monoclonal antibody. ICAM-1 was expressed focally in a honeycomb-like pattern by hepatocytes in livers of 26/27 patients. The degree of ICAM-1 expression was closely related to the ALT level and the histological grade of liver damage. Abundant cytotoxic T cells (CD8 +, CD11b –) were found in ICAM-1-positive areas of the liver. Zones of focal necrosis contained both ICAM-1-positive hepatocytes and cytotoxic T cells. The expression of ICAM-1 was decreased in 4/6 CHB patients after interferon-α therapy. No relationship between the degree of hepatocyte ICAM-1 expression and viral replication markers (DNA polymerase activity and the presence of HBcAg in the liver) was observed in patients with CHB. In addition, no positive correlation was found between the distribution of ICAM-1-positive hepatocytes and HBcAg-positive hepatocytes. These results suggest that ICAM-1 may play an important role in the pathogenesis of hepatocellular injury mediated by cytotoxic T cells in CHB and CHC.