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Purpose: Our purpose was to find the differences in granulosa—luteal cells obtained from gonadotropin- versus gonadotropin-releasing hormone (GnRH) agonist/gonadotropintreated follicles in in vitro fertilization-embryo transfer (IVF-ET) cycles. Methods: Granulosa-luteal cells were obtained from 45 follicles of women undergoing IVF-ET with gonadotropin releasing hormone (GnRH) agonist and human menopausal gonadotropin (hMG) and from 45 follicles of women with hMG IVF-ET cycles. Subpopulations of granulosa-lut eal cells were observed by computerized image analysis in which human chorionic gonadotropin (hCG) was localized using immunoperoxidase staining. Results: The luteinized granulosa-luteal cells from hMGtreated follicles were larger than those from GnRH agonist/ hMG-treated follicles. The hMG-treated follicles contained more hCG-stained cells, particularly those with cytoplasmic hCG localization. Conclusions: We found differences in morphometric characteristics and hCG localization in granulosa-lut eal cells obtained from hMG- versus GnRH agonist/hMG-treated follicles. We presume that the results indicate the influence and importance of luteal-phase support on the clinical pregnancy rate in GnRH agonist/hMG-treated IVF-ET cycles.