The TRA-2-54/2J antibody reacts with the tissue non-specific isoform of alkaline phosphatase (AP), which is expressed at high levels in undifferentiated pluripotent stem cells such as human and mouse embryonic stem (ES) cells, as well as induced pluripotent stem (iPS) and embryonal carcinoma (EC) cells. This isozyme of AP is the same as that expressed by liver, bone and kidney cells. Levels of AP decrease upon differentiation and, thus, the TRA-2-54/2J antibody can be used to monitor the differentiation status of pluripotent stem cells. The TRA-2-54/2J antibody does not cross-react with other isozymes of AP, which differ through post-translational modification, and reportedly does not recognize AP from cow, dog, goat, Guinea pig, hamster, mouse, rat or sheep, or Old World Monkeys such as the rhesus monkey, baboon and African green monkey.