Objective: To investigate the relationship between the incidence of apoptotic bodies in membrana granulosa and follicular steroid concentrations in human follicles.Design: Case-controlled prospective study for 132 individual follicles.Setting: Procedures were performed in Yamagata University Hospital.Patient(s): Thirty-six normo-ovulatory women with tubal infertility underwent ovulation induction for IVF-ET with a conventional hyperstimulation method.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. Intrafollicular steroids were evaluated mainly by RIA. These data were analyzed with respect to oocyte-retrieval, oocyte maturity, fertilization, and embryo quality.Result(s): Membrana granulosa cells in the follicles from which oocytes were subsequently fertilized showed a significantly lower incidence of apoptotic bodies than those in follicles from which the oocytes did not fertilize. Membrana granulosa cells in the follicles from which oocytes were developed into good quality showed a significantly lower incidence of apoptotic bodies than those in the follicles from which oocytes developed into fair and poor quality. The incidence of apoptotic bodies was significantly higher in the mural granulosa cell region than in the cumulus cell region in most cases. Intrafollicular E 2 , P, and free T levels were not different between the oocyte groups.Conclusion(s): These results indicate that lower incidence of apoptotic bodies in individual follicles is associated with better outcomes for oocytes. Also, mural granulosa cells and cumulus cells in each follicle may show differentiation during follicular maturation.