Aim: Despite major advances in assisted reproductive techniques, clinical pregnancy rates remain around 31% with fresh embryo transfer and around 41% with oocyte donations. We also know that the implantation process itself and the window period defined as the ''implantation phase'' are significantly important for successful in-vitro fertilization (IVF) cycles. With this study, we have tried to determine any differences in immunohistochemical staining for CD56 and CD98 within the implantation phase endometrium of patients with recurrent implantation failure and of a control group that eventually had a successful IVF cycle.Material and Methods: This study was retrospectively performed on a total of 36 patients selected out of a database of 6260 patients who received their IVF cycles from 2004 to 2010. Patients were defined as implantation failure if they did not have a positive result for b-HCG testing following at least 3 IVF cycles with a total of at least 8 embryo transfers. The control group was formed with patients who had success (positive b-HCG testing) on their first IVF treatment.Results: Comparison of means for CD 56 staining percentages, CD 98 staining percentages, CD 98 staining power, and CD 98 staining score showed significant difference between the control group and the study group (p˂.001). The endometrium of patients without recurrent implantation failure is significantly more stainable by CD 98 than that of patients with recurrent implantation failure. Discussion: We suggest that CD 56 and CD 98 staining for endometrium tissue can be a part of diagnostic testing for patients who are candidates for IVF treatments. We need further studies to determine the correlation between the overall chance for pregnancy and these types of immunohistochemical staining for patients receiving IVF treatment.