||Despite the vital physiological role of endometrial regeneration during the menstrual cycle and the various pathological implications of abnormal growth of endometrial epithelial cells, the local factors and regulatory mechanisms involved in endometrial regeneration and growth have not been well characterized. Here, we examine the pattern, hormone dependence, and potential functions of Wnt7a (wingless-type MMTV integration site family member 7a), which is known to play a critical role in the formation of the mouse endometrial epithelium during embryonic development, in both human and artificially cycling rhesus macaque endometrium, and using a potent Wnt-antagonist in a mouse model of endometrial regeneration. Wnt7a transcript levels were examined using quantitative real-time PCR and in situ hybridization, and immunohistochemistry was performed to detect Ki-67 and 3,5-bromodeoxyuridine. Stringent, fully conditional Wnt inhibition was achieved by adenoviral expression of Dickkopf-1 during artificial endometrial regeneration in mice. In macaques, Wnt7a expression was confined to the newly formed luminal epithelium (LE) and upper glands during the postmenstrual repair phase. The signal increased in the LE during the proliferative phase but decreased in the upper glands and was undetectable in the glands by the late proliferative phase. Interestingly, Wnt7a was completely suppressed in the LE and remained undetectable in other cell types after 7 d of progesterone treatment. The pattern of Wnt7a expression in the human endometrium was similar to that in macaques. Blockade of Wnt signaling during endometrial regeneration in mice resulted in a dramatic delay in reepithelialization and degeneration of glands and LE. These results strongly suggest, for the first time, a role for Wnt7a in postmenstrual regeneration and proliferation of endometrial glands and LE in primates, and its dramatic suppression by progesterone is likely essential for secretory transformation of the epithelium.