A human hepatoma cell line, HuH-7, which was established from a hepatoma tissue removed at surgical operation from an adult Japanese male, grows autonomously in a serum-free chemically defined medium. A human hepatoma-derived growth factor with potent growth-promoting activity, was partially purified from the conditioned medium of HuH-7 cells, using ion-exchange, heparin affinity chromatography and gel filtration. The partially purified growth factor (HuHGF) is acid- and heat-labile, and sensitive to reduction and trypsin digestion. HuHGF, which is of relatively high molecular weight (about 64 kDa) examined by gel filtration, stimulates not only the DNA synthesis of Swiss mouse 3T3 fibroblasts, but also the growth of HuH-7 cells in serum-free chemically defined medium, suggesting that it is produced by and acts on HuH-7 cells as an autocrine growth factor. This putative growth factor may play an important role in the autonomous growth of hepatoma and may lead to useful diagnostic or therapeutic approaches to human hepatoma.