Since 1933 a number of serologic tests have been made in the study of patients with rheumatic fever, arthritis, and several other diseases, who have come under the authors' care. These tests include gonococcus complement fixation, hemolytic streptococcus agglutinin and precipitin tests, and antifibrinolysin and antistreptolysin titrations. A preliminary report of the results of these was made in 1936 (1). The purpose of the present report is to give a more detailed analysis of the results of antistreptolysin determinations performed from 1933 to the end of 1938.We have determined the titer of the serum of normal subjects and patients with the following diseases: 1. Scarlet fever 2. Rheumatic fever and chorea 3. Rheumatoid and other types of arthritis 4. A few cases of such miscellaneous conditions as erythema nodosum, pericarditis, lupus erythematosus disseminatus, and periarteritis nodosa. The cases studied were from the Third (New York University) Medical Division of Bellevue Hospital and from the Arthritis Clinics of New York University College of Medicine. The sera were analyzed without knowledge of the clinical diagnoses. The serological determinations were done according to the method of Hodge and Swift (2). Because of the time required for antibody formation to take place, no patient with antistreptolysin titer within the normal range was included in our analysis unless serial determinations were made over a period of at least 4 weeks.1 In all, 1,539 determinations have been made on the sera of 817 patients with the diseases listed above. We have also collected and rearranged results 1 Except in the scarlet fever patients, some of whom were followed only 3 weeks. obtained by others for the purpose of convenient reference.