Abstract: Objective:To explore the changes and clinical significance of interleukin-12 (IL-12) in the peritoneal fluid and serum of patients with endometriosis.Methods:IL-12 in the peritoneal fluid and serum of 39 patients with endometriosis and 16 controls were detected by enzyme linked immunosorbent assay (ELISA).Results:IL-12 levels in the peritoneal fluid and serum of the endometriosis group were lower than those of the control group (P<0.01).IL-12 levels in the peritoneal fluid(62.37±13.7) ng/L and in the serum(53.64±17.4) ng/L of patients with stageⅢ-Ⅳ endometriosis were lower than those in the peritoneal fluid(76.38±13.5) ng/Land in the serum(75.67±12.3) ng/L of patients with stageⅠ-Ⅱendometriosis (P<0.01).Conclusions:IL-12 may play an important role in the pathogenesis of endometriosis.Determining the IL-12 levels in patients with endometriosis could help to the diagnosis and treatment.