Objective: To investigate the incidence of apoptotic bodies in mural granulosa cell masses and cumulus cell masses.Design: Nonrandomized, prospective study.Setting: Department of Obstetrics and Gynecology, Yamagata University School of Medicine, Yamagata, Japan.Patient(s): One hundred twenty-nine normally ovulating women underwent ovulation induction for IVF-ET with GnRH analogue (GnRH-a) and gonadotropins.Intervention(s): Patients underwent follicle aspiration after the administration of hCG.Main Outcome Measure(s): The nuclei of recovered granulosa cells were examined by fluorescence microscopy and the incidence of apoptotic bodies was tabulated.Result(s): The incidence of apoptotic bodies was significantly higher in mural granulosa cell masses than in cumulus cell masses in the entire group of 129 patients. Both incidence of apoptotic bodies of mural granulosa cell masses and cumulus cell masses were significantly higher in patients with less than six follicular oocytes compared with patients with six or more oocytes. Nonpregnant patients showed significantly higher incidence of apoptotic bodies in mural granulosa cell masses compared with pregnant patients.Conclusion(s): These results indicate that mural granulosa cell masses and cumulus cell masses may have different functions in follicular maturation. The incidence of apoptotic bodies in mural granulosa cell masses can be used as an indicator of success of IVF.