Epidermal growth factor (EGF) is a well-characterized growth factor that was initially isolated from mouse submaxillary glands.(1–3) The low-molecular-weight growth factor (M r 6000) can be isolated as a component of a high-molecular-weight complex with an associated arginine esterase activity. (4,5) EGF has been found in all mammals and, in humans, is a component of nearly all body fluids.(6,7) A variety of biological responses are mediated by EGF in vivo and in vitro, in a diverse number of cells including epidermal and epithelial cells, which are particularly responsive in the intact animal.(7) It is important to note that almost 90% of all malignancies are derived from epithelial cells.