The cause of rheumatoid (atrophic) arthritis is unknown. Of the many impressions regarding its cause, the microbic hypothesis is still the most widely accepted and, of the many different bacteria which have been incriminated, hemolytic streptococci have been, since 1929, most under suspicion.1 Hemolytic streptococci from time to time have been recovered from the synovial fluid and blood, from foci of infection and occasionally from synovial membrane, bone and lymph nodes of patients with rheumatoid arthritis. The blood of the majority of patients who have this disease contains antibodies against hemolytic streptococci; that is, agglutinins, generally in high titer and precipitins for the C substance of hemolytic streptococci. Although the concentration of antistreptolysins and antifibrinolysins in the blood is not increased, except in some early or acute cases, the skin of patients with rheumatoid arthritis often is found to be hypersensitive to extracts of hemolytic streptococci. Such is the