The TRA-1-81 antibody reacts with a carbohydrate epitope on TRA-1-81, a high-molecular-mass (> 200 kDa) glycoprotein expressed on the surface of human embryonal carcinoma (EC), embryonic germ (EG), embryonic stem (ES), and induced pluripotent stem (iPS) cells, as well as rhesus monkey and rat ES cell lines. No immunoreactivity is observed with mouse EC, EG, ES, or iPS cells. The epitope of the TRA-1-81 antibody is associated with a keratan-sulfated transmembrane protein identified as podocalyxin and is resistant to treatment with neuraminidase.