Primary infection of the endocardium with higher organisms is uncommon. Because of the rarity of this type of infection and the difficulty in establishing the diagnosis, it has seemed worth while to report a case of this disease. This appeared especially desirable since the infection was controlled over a considerable period with sulfonamide compounds, an experience contrary to expectation with mycotic infections. Further, since the isolated cases of mycotic endocarditis reported in the literature had not been previously collected it seemed profitable in connection with a report of a case to make such a collection. REPORT OF CASE A. M., a 14 year old American boy born June 16, 1925, was admitted to the pediatric service of the University of Chicago clinics on April 25, 1940 with the complaint of chills and fever of two weeks' duration. The family history was not contributory; his father, mother and one brother were