A rat hepatoma cell line, FF101, established in serum-free, protein-free medium, synthesizes a growth factor(FF-GF). FF-GF was purified by gel filtration chromatography, cation-exchange chromatography and isoelectric focusing. Purified FF-GF was revealed as a single band on SDS-gel electrophoresis and its molecular weight was estimated to be 70 KDa. FF-GF stimulated DNA synthesis of various cells from different origins. The growth-promoting activities of FF-GF were abolished by treating with protease, dithiothreitol, acid and heating, whereas its activity was not inhibited by antibodies against acidic and basic fibroblast growth factors. These results indicate that FF-GF is a novel growth factor.