Growth factors are pleiotropic, multifunctional cytokines that exert their activity via specific membrane-anchored tyrosine kinases. Growth factors are key regulatory polypeptides in fetal development, wound healing, organ regeneration and are thought to play a major stimulatory role in tumorgenesis. In liver regeneration TGF-alpha and HGF-SF have been identified as activating factors in vivo and their expression and function is tightly regulated. In hepatocarcinogenesis, overexpression of TGF-alpha and IGF-II is frequently present and vast evidence supports their growth stimulatory role at least during later stages of hepatocarcinogenesis.