DURING the past three decades a number of peptide growth factors have been isolated and characterized. Among these are several families of factors: insulin and the insulin-like growth factors, the hematopoetic colony stimulating factors, the fibroblast growth factors, and the epidermal growth factor (EGF) family. All of these are involved in mammalian growth and development. Here we review current understanding of the metabolism and roles of the EGF family of growth factors in mammals. The EGF literature is extensive, and, to limit the current bibliography, review articles have been cited where possible. The human EGF family includes EGF, transforming growth factor-α (TGFα), and amphiregulin. The structures of these factors are shown in Fig. 1. TGFα and amphiregulin have 35—40% homology with EGF (1–4). The vaccinia virus growth factor (Fig. 1) and the myxomavirus and shope fibroma virus growth factors (not shown) have 20–35% homology with human EGF (4).