We studied the relationship between interferon (IFN) therapy and changes with serum titers of Human Hepatocyte Growth Factor (HGF) in hepatitis C patients.[Material and Method] Forty subjects were selected from aged 21 to 69 years, who received IFN alpha with total dose of 324-780 Mega Unit, were positive for serum HCV RNA, and histological diagnosed with CAH. Serum were collected at 4 points of time, i.e., before and just after, and 6 months and 1 year after the therapy. In 5 patients, intrahepatic HGF antigen were investigated by immunoperoxidase method using monoclonal HGF antibody before and 1 year after completing the therapy. Serum titer of HGF were determined with ELISA kits. [Result] 1) Intrahepatic HGF antigens were detected in cytoplasm of Kupffer cell and Macropharge, and were also presant in some of focal necrosis. 2) The mean serum HGF titer was 0.30 for complete responder (CR) and 0.34 for Non responder (NR) with pre-therapy, and the titer of post-therapy were lower than pre-therapy in 83% of all patients, but increased again with time in 45% of NR patients. Serum HGF titer of post-therapy were lower than pre-therapy in 88% of CR patients. and subsequently remained unchanged or decreased in 60% of CR. Briefly, the serum HGF titers were decreased in the majority of hepatitis C patients after IFN therapy and subsequently remained depressed in about half the number of patients, no matter whether patients achieved CR or NR. [Conclusion] The serum HGF titers were decreased after IFN therapy in about half the number of hepatitis C patients, irrespective of therapeutic effect. Serum HGF titer of post-therapy decreased may be anounced for by reduction in the number of mesenchymal cells.