iNOS was not detected, while eNOS exhibited unique menstrual cycle-dependent expression. Women with endometriosis-associated infertility had higher eNOS levels in the eutopic endometrium before GnRH-a treatment compared to controls. After 3 months of GnRH-a therapy, eNOS levels decreased. Additionally, there was a significant positive correlation between serum E2 or p concentrations and endometrial eNOS expression./GnRH-a treatment reduced endometrial eNOS expression in women with endometriosis-associated infertility, with endogenous ovarian steroids affecting this expression. The gene discussed is GNRH1; the disease is endometriosis.