Several lines of evidence indicate that high proliferative bias in eutopic endometrium during secretory phase is a hallmark of endometriosis and that high occurrence of implantation failure in patients resulting in infertility is often associated with endometriosis. ErbB family of proteins, which regulate the proliferation capacity in mammalian cells, appear as potential group of proteins to cause higher proliferation and endometrial hostility to implantation process in endometriosis. However, we have no concrete knowledge regarding the involvement of ErbB family in human endometrium during the ‘implantation window’, i.e., days 20-24 of a typical ovulatory cycle in endometriosis associated infertility. In the present study, the cellular profiles of immunopositive ErbBs-1 to -4 in endometrium of endometriosis-free, infertile women (Group 1; n=11), and in eutopic endometrium of infertile women diagnosed with stage IV ovarian endometriosis (Group 2; n=13) during mid-secretory phase were examined and compared using standardized WERF EPHect guidelines. Computer-aided standardized combinative analysis of immunoprecipitation in different compartments revealed an overexpression of ErbB-1 in the epithelial, stromal and vascular compartments along with marginally higher ErbB-3 expressions (P< 0.06) in the vascular compartment and ErbB-4 expression (P< 0.05) in the glandular epithelium and stroma in endometrium during the window of implantation of women with primary infertility associated with stage IV ovarian endometriosis compared with disease-free endometrium from women. A global overexpression of ErbB-1 in the endometrium during implantation window may induce anomalous proliferative, inflammatory and angiogenic activities in it, which antagonizes endometrial preparation for embryo implantation.