To evaluate basal (constitutive) and stimulated synthesis of tumor necrosis factor α (TNF α ), interleukin (IL)-8, and IL-10 by peritoneal macrophages (PM) in women with endometriosis. Peritoneal macrophages were cultured in the presence or absence of lipopolysaccha-ride (LPS) for 24 hours. Peritoneal fluids (PF) and PM supernatants were assayed for cytokines using ELISA. Institute for the Study and Treatment of Endometriosis and university-based research laboratories. Fertile controls undergoing tubal ligation (n = 8) and women with endometriosis (n = 17). Peritoneal fluid samples were obtained at the time of diagnostic laparoscopy (endometriosis group) or laparoscopy for tubal ligation; both were performed in the midluteal phase of the cycle. Both basal and LPS stimulated production of TNF α , IL-8, and IL-10 by the PM were elevated significantly in women with endometriosis as compared with the fertile controls. This study demonstrated that cytokines TNF α , IL-8, and IL-10 are synthesized at greater than normal levels by basal and stimulated PM from women with endometriosis. The levels of TNF α and IL-8 correlated with the levels in the PF, suggesting that PM are the principal source of these cytokines in the PF.