During early pregnancy, the endometrium undergoes pronounced hormone-dependent functional changes in preparation for embryo implantation. Local autocrine-paracrine signaling at the fetal-maternal interface is crucial for the establishment of pregnancy. We previously reported that the transcription factor C/ EBPbeta, which is expressed at the implantation sites (ISs) in pregnant mice, acts as a key mediator of steroid hormone responsiveness in the endometrium. Mice lacking C/EBPbeta fail to support implantation due to defects in epithelial proliferation and stromal cell differentiation. In the current study, C/EBPbeta expression was dramatically stimulated in the endometrium of baboons (Papio anubis) during the window of uterine receptivity in response to a local infusion of chorionic gonadotropin, an embryonic signal. A robust induction of C/EBPbeta expression was also seen at the IS in the baboon and the human. Collectively, our results indicate that C/EBPbeta is a biomarker of endometrial receptivity and plays a conserved functional role during implantation in the primate.