This review describes the discovery and initial characterization of the epidermal growth factors (EGFs) and transforming growth factors α (TGFα), biosynthesis and tissue distribution of these molecules and a brief discription of the effects of these molecules in culture and animals. An analysis of the similarities between the EGFs and TGFαs from different organisms in used to describe the features of the molecules which appear to be critical for their function. The review concludes with discussion of the relationship between the production of the EGF or TGFα to cancer indcution and/or matastasis.