The importance of performing an endometrial biopsy in women preparing for oocyte donation goes beyond confirming the histologic response to hormone replacement therapy. Additional information related to uterine architecture, ease of embryo transfer, status of the ovaries, and patient compliance is also gained. Finally, the return visit provides an opportunity to discuss plans for the upcoming cycle. Whereas this report does not specifically address the question as to how many pregnancies were contingent upon the satisfactory performance of the mock cycle, we estimate that due to a combination of factors (i.e., lack of endometrial response, patient noncompliance, difficult embryo transfer), the likelihood of pregnancy in many cases would have been substantially reduced had the preliminary cycle not been attempted.