A humanized monoclonal antibody directed against human heparin-binding EGF-like growth factor (HBEGF) with potential antineoplastic activity. Anti-HBEGF monoclonal antibody U3-1565 binds to HBEGF and blocks the binding of HBEGF to the EGF receptors. This prevents EGF receptor activation and the subsequent induction of cell growth signaling. HBEGF is mitogenic for fibroblasts and smooth muscle and may be involved in macrophage-mediated cellular proliferation.