This antibody reacts with the Stage-specific embryonic antigen-4 (SSEA-4) that is expressed upon the surface of human teratocarcinoma stem cells (EC), human embryonic germ (EG) cells) and human embryonic stem (ES) cells. No immunoreactivity is evident with undifferentiated murine EC, ES and EG cells. Expression of SSEA-4 is down-regulated following differentiation of human EC cells. In contrast, the differentiation of murine EC and ES cells may be accompanied by an increase in SSEA-4 expression.