ABSTRACT Objective — to compare the levels of metalloproteins (MMP) 1 and 9 and CD45 in the eutopic and ectopic endometrium of patients with endometriotic cysts and normal endometrium of women without endometriosis. Material and methods. The study included 94 patients of reproductive age who were divided into 2 groups: the I group consisted of 70 patients with endometriotic ovarian cysts, II group — 24 patients with infertility of unspecified genesis without endometriosis (comparison group). All patients of the I group underwent endoscopic removal of the endometriotic cyst, salpingoovariolysis, hysteroscopy with material extraction for morphological and morphometric studies. Patients of the II group underwent laparoscopy with chromohydrotubation and hysteroscopy, sampling of the endometrial biopsy for histological, morphological and morphometric studies. Conclusions. A comparative immunohistochemical study of MMP and CD45 in normal, eutopic and ectopic endometrium improved our understanding of pathogenesis of endometriosis. The increased proliferative activity of eutopic endometrium in comparison with normal is indicated by the increase of matrix metalloproteinases in the eutopic endometrium, and the revealed increased level of CD45 expression in the ectopic endometrium in comparison with eutopic endometrium is evidence of the inflammatory process in the endometrioid cysts.