Heparin binding EGF (HB-EGF) is a member of the EGF family of mitogens which also include transforming growth factor alpha (TGF-alpha), amphiregulin (AR), rat schwanoma-derived growth factor (SDGF), vaccinia growth factor (VGF), and the various ligands for the HER2/erbB2/neu receptor. Many of these transmembrane precursors are biologically active and seem to play a role in juxtacrine stimulation of adjacent cells.