A human/murine chimeric monoclonal antibody directed against endoglin (CD105) with potential antiangiogenic and antineoplastic activities. Anti-endoglin monoclonal antibody TRC105 binds to endoglin, which may result in inhibition of tumor angiogenesis and decreased tumor cell proliferation. The glycoprotein endoglin is a transforming growth factor beta-1 (TGF beta-1) accessory receptor that is highly expressed on tumor vessel endothelial cells and appears to be essential for angiogenesis.