Amphiregulin, like other ErbB ligands, is synthesized as a pro-protein which requires cleavage at the cell surface to release the active signaling domain. Prior studies using a variety of approaches have not yielded a consensus about the precise cleavage site. Here we report the purification and protein sequencing of the cell-associated human Amphiregulin stalk which remains following cleavage of the signaling domain. These data indicate that human Amphiregulin is cleaved at Lysine 187, a site homologous to the cleavage site reported in the mouse protein and distinct from the Lysine 184 site previously reported for the human protein. © 2012 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.