Hepatocyte growth factor (HGF), a potent mitogen for hepatocytes, is a hepatotrophic factor for liver regeneration. Addition of heparin to cultures of human fibroblasts, leukemic cells, and umbilical vein endothelial cells stimulated HGF production to 3-6-fold higher levels than seen in the absence of heparin. Administration of heparin to rats increased blood HGF levels to a 2.5-5-fold higher level than that in control rats given saline alone, and consequently induced a remarkable enhancement of liver regeneration in vivo after a 30% partial hepatectomy. However, heparin had no stimulatory effect on DNA synthesis of hepatocytes in primary culture. These results indicate that heparin has hepatotrophic function, an action possibly mediated through the stimulation of production of HGF.