L-selectin ligands were detected in the epithelial endometrium throughout the implantation window, whereas the level of expression was significantly reduced in the donor versus control group on cycle day 19 (P<.05) in the luminal epithelium and during cycle days 19-24 in the glandular epithelium. Controlled ovarian stimulation, using the antagonist protocol in this study, is associated with a reduction of L-selectin ligand expression during the implantation window which may adversely affect the endometrial environment.