We determined hepatocyte growth factor (HGF) levels in the serum and liver of patients with hepatitis C and assessed the relationship to histological findings of the liver and hepatitis C virus-related markers in the serum in patients with type C liver diseases. The subjects were 108 patients with chronic hepatitis C (CH), 70 patients with liver cirrhosis C (LC), 38 patients with hepatocellular carcinoma (HCC) and 20 patients with acute hepatitis (AH). As normal controls 20 subjects were studied. The serum HGF levels were measured using an enzyme-linked immunosorbent assay kit. Intrahepatic HGF was investigated by immunoperoxidase staining using monoclonal HGF antibody. The serum HGF level was highest in patients with AH. The serum HGF levels tended to be higher in patients with LC and HCC than those with CH. Further, the serum HGF level was related to the degree of intrahepatic inflammatory cell infiltration and fibrosis, and intrahepatic HGF was noted primarily in the cell membrane of mesenchymal cells in focal necrosis. The degree of intrahepatic HGF expression tended to be higher in patients with high serum HGF levels. In patients with HCC, however, HGF showed little localization in cancer cells, but was noted in infiltrating mesenchymal cells in both cancerous and noncancerous regions. In conclusion, the measurement of serum HGF levels may be useful for estimating the degree of intrahepatic inflammatory reaction and fibrosis. Although further study is necessary, the high serum level of HGF revealed high carcinogenic states in chronic hepatitis and liver cirrhosis type C.