Antibodies against Chlamydia trachomatis were detected with the immunoperoxidase assay (IPA) in 32 patients suffering from rheumatic diseases. In this test the cells infected with Chlamydia trachomatis serotype L2 were the antigen. In addition all sera were tested for anticellular antibodies, using non-infected cells as antigen. 13 out of these 32 IPA-positive patients (41%) were also positive with respect to anticellular antibodies.