Summary1. Antibacterial action ofPenicillium Notatumagainst streptococcus viridans has been pointed out by Fleming in bis original studies.2. Clinical experiments in order to treat subacute bacterial endocarditis were started in 1942. However, it was only in 1944 that the first favourable results were published.3. The last two important publications report respectively 30 cases of recovery on 35 and 12 cases on 15.4. It is necessary to have a definite plan of treatment : to know the nature of the responsible micro-organism and its resistance towards penicillin; to give doses which permit to reach adequate concentrations in the blood stream (at least 4 times the value of the resistance of the micro-organism).5. It is interesting to verify the concentration in the serum. If necessary tables may be consulted which give the relations between the injected doses and the concentrations reached in the serum.6. It has recently been pointed out that the natrium salt of para-amino-hippuric acid permits to multiply by 6 the concentration of penicillin in the bloodstream.7. Penicillin may be given by continuous intramuscular or intraveinous injections and by intermittent intramuscular injections. The latter are far the better if they are used every hour or even every other hour. However, if it is necessary to give natrium salt of para-amino-hippuric acid at the same time, continuous intravenous injections must be used.8. The treatment is continued for three weeks. The result is almost always favourable if the concentration in the bloodstream has been well established. In case of failure, a new one is made after having reexamined the resistance of the micro-organism. Furthermore, this time, a concentration in the bloodstream more than 4 times the resistance of the microbe (between 5 and 10 times) must be obtained. Treatment must not be abandoned, even if 5 successive cures remained without result.9. Recurrences must be prevented by exclusion of possible foci of reinfection (nasopharynx, teeth and others). Anti-infectial measures must be taken before, during and after surgical intervention by giving penicillin or if not available sulfamides.If subacute bacterial endocarditis is engrafted on patent ductus arteriosus, it must be tied 15 days after injection has been cured. All these prophylactic measures may be also taken in case of patients who never bad subacute endocarditis but who are susceptible to get this disease.10. Heparin is not a sufficiently interesting factor to justify the additional effort and the risks of hemorrhage implicated by the use of it. Nevertheless, it is used in small doses to avoid apparition of local thrombophlebitis when one is compelled to give penicillin intravenously.