Objective: The aim of the study was to evaluate the endometrial receptivity by using alpha v beta 3 expression in the midsecretory phase in different endometrial compartments in women with unexplained infertility. Study design: A prospective controlled clinical trial in a setting of a university teaching hospital was performed. Thirty-three fertile and 33 infertile women were included in the study. Midluteal endometrial biopsies of the endometrium were carried out during the implantation window. Immunohistochemical staining was performed for the expression of alpha v beta 3 in endometrial samples. alpha v beta 3 expression was measured using the HSCORE scoring system in the endometrial glandular and luminal epithelium and in the endometrial stroma. Serum levels of estradiol, progesterone, follicle-stimulating hormone, luteinizing hormone, thyroid-stimulating hormone, prolactin, total testosterone and dehydroepiandrosterone sulphate were measured in the early follicular phase and in the midluteal phase. Results: The average alpha v beta 3 integrin expression at different sites of the endometrium was not different in the infertile and fertile controls. However, the stromal alpha v beta 3 integrin was found to be expressed significantly less in a subgroup of women with lower than average alpha v beta 3 integrin expression in luminal epithelium than in fertile controls and significantly more in a subgroup of women with higher than average alpha v beta 3 integrin expression in luminal epithelium. There was no difference in stromal alpha v beta 3 integrin expression in the lower or higher glandular alpha v beta 3 integrin expression subgroups. Conclusions: alpha v beta 3 Integrin expression in endometrial stromal cells may be different in subgroups of women with unexplained infertility. (C) 2005 Elsevier Ireland Ltd. All rights reserved.