Objective: To evaluate how endometriosis affects the expression of estrogen and progesterone receptors mRNA in granulosa cells. Design: Prospective study. Setting: IVF-ET program at Osaka Medical College. Patient(s): Eighteen patients with revised American Fertility Society stage IV endometriosis and 23 patients with tubal infertility without endometriosis. Intervention(s): Granulosa cells obtained from patients with endometriosis were examined for estrogen (ER-beta, ER-alpha) and progesterone (PR-A, PR-B) receptor mRNA expression ratio against GAPDH. Main Outcome Measure(s): Hormonal environment and clinical outcome were investigated. Expression of ER and PR mRNA were evaluated by StepOne real-time polymerase chain reaction (PCR) analysis. Result(s): Total hMG/FSH levels were statistically higher in patients with endometriosis; however, high-quality embryo rates and pregnancy rates were lower in patients with endometriosis than in patients with tubal infertility. Expression of PR-A and ER-alpha in patients with endometriosis was statistically higher than in patients with tubal infertility. The expression of PRs and ERs in patients with tubal infertility showed a positive correlation; however, it was not identified in the endometriosis group. Conclusion(s): The higher PR-A and ER-alpha gene expression in granulosa cells in patients with endometriosis, compared with patients with tubal infertility, might be a leading cause of ovarian dysfunction due to endometriosis. (Fertil Steril (R) 2011; 95: 889-94. (C) 2011 by American Society for Reproductive Medicine.)