Human EGF is a 53 amino acid long fragment of the extracellular domain of EGF precursor. As other group 1 members, EGF binds to, and activates the EGF receptor. This promotes EGFR dimerization. EGF has variety of diverse physiological effects. EGF activity is complicated by the fact that other EGF family members utilize EGF receptor. EGF stimulates the growth of various epidermal and epithelial tissues in vivo and in vitro and of some fibroblasts in cell culture. EGF is proposed to affect growth and/or differentiation of many other fetal and adult tissues.