The overall goal of this proposal is to assess modulation of immune mechanisms in endometriosis. Endometriosis is a common ailment affecting approximately five million reproductive-aged American women. We will test the efficacy of a novel immunomodulatory drug (peroxisome proliferator activated receptor gamma, PPAR-gamma, agonist), rosiglitazone, to reduce peritoneal fluid cytokine concentrations in women with endometriosis compared with placebo controls (randomized controlled trial). Based on prior studies done by the investigator highlighting the major role of cytokines and the immune system in the genesis or propagation of endometriosis, these experiments could lead to improved translational treatment strategies and a better understanding of endometriosis. Acting through PPAR-gamma, TZDs inhibit proinflammatory cytokines as well as NF-kB, an important nuclear transcription factor for the production of many cytokines. Accordingly, since human endometrial epithelial and stromal cells contain PPAR-gamma, we felt it would be useful to evaluate the influence of a PPAR-gamma ligand, rosiglitazone, on the concentration of specific peritoneal fluid cytokines.