The significance of retrograde menstruation as a risk factor for endometriosis has been confirmed by numerous clinical observations. Integrins mediate both cell-cell and cell-matrix adhesion, and it is therefore suspected that integrins are involved in the development of endometriosis. Using immunohistochemistry, integrin expression in eutopic and ectopic endometrium is examined in endometriosis patients and control individuals. In nearly all cases, the glandular epithelial cells in the endometrium showed expression of α2-, α3-, α6- and αv- integrin and a low percentage of expression of α1-, α4-, and α5-integrin. In comparison with eutopic endometrium, ectopic endometrium shows reduced expression of α2- and αv-integrin. Since no differences in α2- and αv-integrin expression were observed in eutopic endometrium between endometriosis patients and control individuals, it may be suspected that the reduced expression of these in ectopic endometrium is explained by influences in the altered environment - e. g., in the peritoneal fluid - on the ectopic endometrium.