The hepatocellular expression of the carbohydrate antigen sialyl monomeric Lewis X (SMLex) and sialyl oligomeric Lewis X(SOLex) in chronic hepatitis was examined using specific monoclonal antibodies. Both of these sialyl Lewis X (SLex) antigens were membranously expressed in chronic hepatitis in spite of their absence in normal liver. Although SMLex was detected in mild hepatic inflammation, the expression of SOLex was associated only with moderate to severe necroinflammation. Hepatocellular expression of these antigens increased significantly as histological diagnosis advanced. Chronological observation also showed the change of SLex expression according to the histological change. The present observations suggest that hepatocellular SLex is a novel histological marker with a close correlation to the severity of necroinflammation in chronic hepatitis.