Objective: The purpose of this study was to evaluate whether pregnancy-associated plasma proteinA, glycodelin,osteoprotegerin, and soluble CD163 are possible peritoneal factor fluid markers for endometriosis and to compare them with the established chemokine markers interleukin-8 and regulated on activation, normal T-cell expressed and secreted factor. Study design: Determination of the concentrations of interleukin-8, regulated on activation, normal T-cell expressed and secreted, pregnancy-associated plasma protein A, glycodelin,CD163, osteoprotegerin, and progesterone in the peritoneal fluid collected from women undergoing laparoscopy. Results: From a total of 132 women, 77 women were diagnosed with endometriosis, and 55 women were free of the disease and served as control subjects. Pregnancy-associated plasma protein A and osteoprotegerin showed significantly(P < 0.05) elevated peritoneal fluid concentrations as a function of the severity of the disease, together with interleukin-8 and regulated on activation, normal T-cell expressed and secreted(P < .001). Glycodelin and CD163 did not differ between cases and control subjects. Many of these marker concentrations were intercorrelated strongly. Conclusion: Pregnancy-asso- ciated plasma protein A and osteoprotegerin may play a role in the inflammation process of endometriosis, but interleukin-8 and regulated on activation, normal T-cell expressed and secreted are superior peritoneal fluid markers. Objective: The purpose of this study was to evaluate whether pregnancy-associated plasma protein A, glycodelin, osteoprotegerin, and soluble CD163 are possible peritoneal factor fluid markers for endometriosis and to compare them with the established chemokine markers interleukin-8 and regulated on activation, normal Study design: Determination of the concentration of interleukin-8, regulated on activation, normal T-cell expressed and secreted, pregnancy-associated plasma protein A, glycodelin, CD163, osteoprotegerin, and progesterone in the peritoneal Results from a total of 132 women, 77 women were diagnosed with endometriosis, and 55 women were free of the disease and served as control subjects. Pregnancy-associated plasma protein A and osteoprotegerin showed significantly (P < 0.05) elevated peritoneal fluid concentrations as a function of the severity of the disease, together with interleukin-8 and regulated on activation, normal T-cell expressed and secreted (P <.001). Glycodelin and CD163 did not differ between cases and control subjects. Many of these marker concentrations were intercorrelated strongly. Conclusion: Pregnancy-asso- ciated plasma protein A and osteoprotegerin may play a role in the inflammation process of endometriosis, but interleukin-8 and regulated on activation, normal T-cell expressed and secreted are superior peritoneal fluid markers.