Human embryonic lung fibroblasts (MRC5) produced scatter factor which enhanced motility of Madin-Darby canine kidney (MDCK) epithelial cells and a factor which stimulates DNA synthesis of adult rat hepatocytes in primary culture. These activities were both completely neutralized by antibody against human hepatocyte growth factor (HGF). Human recombinant HGF induced a marked scattering of MDCK cells. Moreover, MRC5 cells highly expressed 6kb mRNA which hybridized with HGF cDNA probe and scatter factor cDNA cloned from the MRC5 cDNA library had the same sequence as that of HGF cDNA from human leukocytes. These results indicate that HGF possesses scatter factor activity and the scatter factor derived from the MRC5 cells is probably identical to HGF.