['To investigate host immunologic response to endometriosis in terms of intercellular adhesion molecule (ICAM)-1 expression by macrophages and killer cell inhibitory receptor (KIR) expression by natural killer (NK) cells.', 'Case-control study of immunologic markers.', 'University hospital.', 'Twenty-eight Japanese women with endometriosis. Control subjects were 26 women without endometriosis. Diagnoses were made at laparoscopy.', 'Venipuncture and laparoscopic peritoneal fluid collection.', 'ICAM-1 expression by macrophages and KIR expression by NK cells, measured by flow cytometry.', 'In women with endometriosis, expression of ICAM-1 by peritoneal macrophages was significantly lower and expression of KIR by NK cells in peritoneal fluid and peripheral blood was significantly higher than in control subjects.'] Does aberrant expression of intercellular adhesion molecule-1 and killer inhibitory receptors induce immune tolerance in women with pelvic endometriosis?