STUDENTS of rheumatic fever disagree in regard to adequate clinical and laboratory criteria for diagnosis during various stages of the disease. Because geographic location, climate, altitude, age, genetic factors, duration of the disease, and other variables enter into the complex picture of rheumatic fever, the correct diagnosis often eludes detection for some time. Studies of the clinical nature of this disease are needed. It is sine qua non that experimental observations be made from a clearly defined source. An accurate diagnosis is equally important to the clinician who is concerned with the evaluation of treatment programs designed to limit the crippling and lethal effects of progressive rheumatic carditis. The present study was undertaken, therefore, in order (a) to define the current clinical and laboratory picture of rheumatic fever in the Rochester area and (b) to describe the clinical material on which a large number of experimental observations have been based.