Objective: To compare levels of insulin-like growth factor (IGF) components in the peritoneal fluid of patients with and without endometriosis.Design: Patients with endometriosis were compared with control patients.Setting: Seoul National University Hospital, Korea.Patient(s): Forty-three patients with endometriosis and 20 patients without endometriosis.Intervention(s): Peritoneal fluid specimens were collected.Main Outcome Measure(s): Insulin-like growth factors, IGF binding protein (IGFBP) profiles and IGFBP-3 protease activity.Result(s): The IGF-I levels in peritoneal fluid were significantly higher in patients with endometriosis than in control patients, while the IGFBP-3 levels and the relative proportion of IGFBP-2 in peritoneal fluid were significantly lower in patients with endometriosis than in control patients. However, IGF-II levels, IGFBP-4 profiles, and IGFBP-3 protease activity did not differ significantly between the two groups. No correlation between these IGF components in peritoneal fluid and the stage of endometriosis was noted.Conclusion(s): The profiles of IGF components in peritoneal fluid of patients with pelvic endometriosis may play an important role in the growth of ectopic endometrium and endometriosis-induced infertility.