Abstract 1.1. In the year 1946 ten patients with subacute bacterial endocarditis due to nonhemolytic streptococcus were admitted to this hospital. All have achieved cures with the use of penicillin. 2.2. Five of the ten patients had had recent dental work prior to onset of the illness which probably precipitated the infection. 3.3. Treatment should not be started until a positive blood culture is obtained and the organism isolated for further study. 4.4. Both aerobic and anaerobic blood cultures should be made. 5.5. Patients should be started on a minimum of 75,000 to 100,000 units of penicillin every three hours since in this series smaller doses were found inadequate. The minimum daily dose that should be administered is at least 600,000 units of penicillin per twenty-four hours. This also may be given in the form of slowly absorbable, procaine penicillin preparations. 6.6. Valuable information can be obtained by checking blood penicillin levels and penicillin resistance of the organism. 7.7. The intermittent intramuseular method of administration of penicillin is the preferred method. 8.8. It is best that foci of infection should be removed toward the latter part of treatment when the penicillin blood level is still high. 9.9. Prophylactically, patients with chronic valvular heart disease or congenital heart disease should be treated with penicillin or a sulfonamide preparation before, during and after removal of foci of infection in order to avoid subacute bacterial endocarditis.