Globin switching of erythrocytes during primate (human and monkey) hematopoietic development has been most thoroughly investigated not only as a model of tissue- and temporally specific transcriptional control but also as a tool for drug discovery against hemoglobinopathies. However, the regulatory mechanisms of globin switching in primates remains to be unresolved in primates mainly due to lack of available model system to date which reproduces the process of hematopoiesis to reflect accurately in vivo development. Recently primate ES cell lines were established, which are expected to serve as an experimental model for tissue growth and development, along with an efficacy and toxicity screening system for new drugs and a cell source for regeneration therapy. Among them, we previously demonstrated that the transition from primitive into definitive erythropoiesis was induced from primate ES cells by coculture with OP9 stromal cells. We also demonstrated that the VEGFR-2high CD34+ cells, emerging onto OP9 stromal layer after initial 6-day differentiation, contain the hemogenic progenitors.