Twenty-eight patients with chronic polyarthritis, II patients with ankylosing spondylitis and II patients with incipient chronic polyarthritis were examined clinically, by electrocardiography, two-dimensional and TM echocardiography for cardiac involvement. Immunological investigations included determination of homologous and heterologous antimyolemmal (AMLAs), antifibrillary (AFAs) and antinuclear (ANAs) antibodies. Patients with cardiac involvement demonstrated homologous and heterologous antimyolemmal antibodies against the cardiac membrane, particularly of the IgM subclass. AMLAs of high titre were not found in patients with rheumatic diseases without cardiac involvement.