Perforin and granzyme A are the major effectors of cytotoxic T cells in cell-mediated cytotoxicity. However, there has been no report on these effectors in chronic viral hepatitis. In the present study, the expression of perforin and granzyme A mRNA was investigated by the reverse transcription polymerase chain reaction method using liver biopsy specimens and peripheral mononuclear cells (PBMC) from 21 patients with chronic hepatitis C and 5 control cases. Perforin mRNA was detected only in the liver of chronic hepatitis patients but not in the control livers. Conversely, perforin mRNA was not expressed in PBMC of the patients with chronic hepatitis (P < 0.01). Granzyme A mRNA was detected both in the liver and PBMC of all the cases including control cases. These results indicated that the perforin is an important effector molecule in the hepatocyte lysis in chronic viral hepatitis C.