The receptor for epidermal growth factor (EGF) has been the subject of intense study primarily as a consequence of the pioneering studies of Cohen on growth factors and also because of its homology to the transforming protein encoded by the avian oncogene v-erbB, which is a truncated receptor and its consequent role in cancer. Although similar structural mutation of the EGF receptor has not yet been found in human tumours, aberrant overexpression of both EGF receptors and c-erbB2, a closely related putative receptor, have been found to occur in squamous cell carcinomas and glial tumours, and mammary carcinomas respectively. In addition to EGF, the related polypeptides transforming growth factor alpha (TGF alpha) and vaccinia virus growth factor are also ligands for the EGF receptor. Expression of TGF alpha occurs during embryonal development and in specific adult tissues; it may also play a role in cellular transformation These important properties, as well as the potential roles of both TGF alpha and EGF in wound repair, have emphasized the need to understand EGF receptor structure, function and regulation. This review discusses the structural properties of the EGF receptor and how these can be related to receptor function and regulation.