The expression of gene products of the major histocompatibility complex (MHC) on the cell surface is known to play an important role in immunological responses. While some studies have reported the presence of MHC antigens on hepatocytes, information about specific, sensitive hepatocyte MHC antigen expression in various liver diseases is minimal. To investigate the expression of class I and class II MHC antigens on hepatocellular carcinoma (HCC) specimens, two-color flow cytometry was used to demonstrate MHC antigen expression on non-malignant and malignant hepatocytes using the hepatocyte-specific monoclonal antibody (MAb) 9B2 for selective gating and either MHC-specific W6/32 (class I) or Q5/13 (class II) MAb for MHC antigen detection. Non-malignant liver tissues demonstrated variable MHC antigen expression. Malignant hepatocytes isolated from resected HCC specimens as well as non-tumorous hepatocytes from these HCC specimens also disclosed various degrees of MHC antigen expression. Although we were not able to demonstrate a clear correlation between clinical outcome and MHC antigen expression in HCC, we conclude that the expression of MHC antigens on human hepatocytes and hepatoma cells can be accurately detected by flow cytometry using hepatocyte-specific MAb for selective gating and MHC-specific MAbs. Of note, two cases of non-malignant fetal liver tissues indicated that G95% of fetal hepatocytes expressed class I MHC antigens and F25% of fetal hepatocytes expressed class II MHC antigens. These findings may lead to further investigations into the progression of HCC cells or into the possible mechanisms of the hepatocellular carcinogenesis.