Sera from 42 patients complaining of infertility were evaluated by indirect immunofluorescence for the presence of antibodies to the endometrium. The presence or absence of antibodies was matched with the findings at laparoscopy. Of the 42 patients examined for infertility, 28 (66.7%) had laparoscopic findings that corresponded to the presence or absence of endometriosis. Of 28 patients with positive antibody tests, 24 (85.7%) were found to have endometriosis. No correlation between the degree of immunofluorescence and the clinical severity of endometriosis could be determined. These findings suggest the possibility of developing a noninvasive immunological test for the presence of endometriosis.