Epidermal Growth Factor (EGF) is a small growth factor containing 53 amino acid residues capable of stimulating the proliferation of both mesenchymal and epithelial cells. The mature protein is much smaller, only 53 aa, and is generated by proteolytic cleavage of the EGF domain proximal to the transmembrane region. EGF is well conserved across mammals with mature human EGF 70% identical to mature mouse and rat EGF. EGF and fibroblast growth factor 2 (FGF-2) induce the proliferation of neural precursor cells isolated from specific regions of the embryonic and adult brain. EGF and somatomedin C-supplemented medium was shown to be capable of replacing the progression activity of 5% platelet-poor plasma (PPP) for competent density-inhibited BALB/c-3T3 cells. Biological activities ascribed to EGF include epithelial development, angiogenesis, inhibition of gastric acid secretion, fibroblast proliferation, and colony formation of epidermal cells in culture.