Human skin fibroblasts secreted a certain amount of human hepatocyte growth factor (hHGF), as determined by an enzyme-linked immunosorbent assay for hHGF. This hHGF secretion was remarkably stimulated by protein kinase C (PKC)-activating phorbol esters, which was inhibited by the simultaneous addition of dexamethasone. Pretreatment with phorbol 12-myristate 13-acetate (PMA) caused a down-regulation in hHGF secretion. hHGF secreted by the PMA-treated cells showed a potent hepatocyte growth-promoting activity which was neutralized by an anti-hHGF antiserum. These results indicate both that PMA-treated human skin fibroblasts produce biologically active hHGF and the possible involvement of PKC activation in this process.