Examination of 631 infertile women, including 434 women with endometriosis and 197 without endometriosis, revealed an increasing incidence of endometrial polyps, especially in the test subjects with endometriosis, and advanced stages of endometriosis. Expression of Ki-67 and Bcl-2 proteins and MTT assay results were significantly higher in endometrium of patients with endometriosis than in patients without endometriosis. These showed increased proliferation activity and cell proliferation markers not only clinically but also pathologically.