Various kinds of growth factors are involved in the regulation of human keratinocyte function. Among them, the epidermal growth factor (EGF) family and the transforming growth factor-beta (TGF-beta) family play central roles, providing dual-mode regulation of keratinocyte growth through the proliferation-stimulating effect of EGF and the proliferation-inhibiting effect of TGF-beta. Human keratinocytes synthesize four EGF family growth factors, TGF-alpha, amphiregulin, HB-EGF and epiregulin, which efficiently regulate keratinocyte growth and differentiation via auto- and cross-induction pathways. Human keratinocytes also synthesize TGF-beta1 and TGF-beta2, which are potent inhibitors of human keratinocytes. These intrinsic EGF family growth factors and TGF-betas are responsible for the autonomous growth regulation of keratinocytes.