OBJECTIVE To evaluate in vitro the production of monocyte chemotactic protein-1 (MCP-1) by endometrial cells of patients with and without endometriosis. METHODS Primary cultures of stromal and epithelial cells isolated from human endometrium were exposed during 24 hours to different cytokines. Monocyte chemotactic protein-1 secretion was analyzed in the culture medium. METHODS Gynecology clinic and laboratories of endocrinology of reproduction and immunology. METHODS Women presenting for infertility or pelvic pain in which endometriosis was diagnosed at laparoscopy (n = 6) and women presenting for tubal ligation without laparoscopic evidence of the disease (n = 6). METHODS None. METHODS De novo secretion of MCP-1 in the culture supernatant by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis after metabolic labeling with 35S-cysteine. RESULTS The incubation of endometrial epithelial cells of endometriosis women with either interleukin-1 beta or tumor necrosis factor-alpha resulted in the appearance of at least two and sometimes three bands having approximately 15, 13, and 9 kd molecular weights. These bands were identified as three distinct species of MCP-1 as their immunoprecipitation was prevented effectively in presence of an excess of cold MCP-1. In contrast, the endometrial epithelial cells of only one of six normal women produce significant levels of MCP-1 under the same stimulation conditions. The stromal cells of both groups of subjects do not secrete appreciable amounts of MCP-1 or only small quantities in two cases of endometriosis. CONCLUSIONS Monocyte chemotactic protein-1 secretion is upregulated in cytokine-stimulated endometrial epithelial cells of women having endometriosis as compared with normal women without evidence of the disease. Such a difference at the level of eutopic endometrial cell may have a significance in the physiopathology of endometriosis.