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(P0.01).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/L]and in the serum [(75.67±12.3)ng/L] of patients with stageⅠ-Ⅱendometriosis(P0.01).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.