Adhesion molecules regulate the interaction of cells with the extracellular matrix and/or other cells. The intercellular adhesion molecule-1 (ICAM-1; CD54) is a member of the immunoglobulin superfamily and expressed by several cell types, including leukocytes and endothelial cells. A circulating form of the usually membrane-bound molecule was identified and characterized in normal human serum and in sera from patients with endometriosis. In the present study, we established the serum-soluble ICAM-1 (sICAM-1) levels in patients with endometriosis. We also studied the effect of danazol and leuprorelin acetate depot on the levels of sICAM-1. Thirty-eight women, 18-45 years of age, with regular menses and documented pelvic endometriosis were recruited from a University Hospital setting. Twenty-two women with endometriosis were randomly divided into two groups. Danazol (600 mg) were given every day for 6 months, and 3.75 mg of leuprorelin acetate depot every 28 days for 6 months. Serum sICAM-1 concentrations were measured before, during and after treatment, and its quantitative determination was performed by an ELISA technique using a specific immunoassay. We found that (1) sICAM-1 levels were higher in women with endometriosis in comparison to healthy subjects; (2) the 6 month treatment with danazol or leuprorelin acetate depot increased sICAM-1 levels (P<0.001); (3) 3 months after termination of both treatments, sICAM-1 levels were unchanged. Although the mechanism leading to the increase of sICAM-1 needs to be further clarified, any benefits of medical treatment of endometriosis such as danazol or leuprorelin appear to be independent of changes in ICAM-1 serum levels.