The stroma of hepatocellular carcinomas (HCC) is infiltrated with myofibroblasts (MFs). Preliminary in vivo data have suggested that liver MF express hepatocyte growth factor (HGF), a cytokine that has been implicated in several tumor models. Our aim was to investigate the role of MF and HGF in HCC. Cultured liver MF expressed HGF messenger RNA (mRNA) and secreted HGF in their medium, as shown by Western blot, immunoprecipitation, and enzyme-linked immunosorbent assay (ELISA). Addition of MF-conditioned medium to the HepG2 HCC cell line induced cell scattering. This was associated with a decrease in cell proliferation. MF also increased about 100-fold the ability of HepG2 to invade Matrigel. Increased invasiveness was also shown for HuH7 cells, but no scattering was observed and cell proliferation was stimulated. All the effects of MF on both tumor cell types were blocked by addition of an antibody to HGF and they all could be reproduced by adding recombinant HGF to the tumor cells. RT-PCR and Western blot analysis confirmed that both tumor cell lines expressed c-met, the receptor for HGF. The effects of MF-conditioned medium were not reproduced by acidic fibroblast growth factor, basic fibroblast growth factor, epidermal growth factor (EGF), transforming growth factor-beta1 (TGF-beta1), or platelet-derived growth factor (PDGF-BB). Reverse transcription-polymerase chain reaction (RT-PCR) analysis confirmed that HGF was expressed in human HCC. Our data show that human liver MF act on HCC cells to increase their invasiveness and suggest that MF-derived HGF could be involved in the pathogenesis of HCC.