1. In the present paper the AA. report a case of endocarditis and septicemia along with the isolation of a diphtheroid bacterium from the blood in vita, as well as from the endocardic changes, blood, spleen and kidneys post mortem. 2. The mentioned bacterium presents special features and, owing to the hemolytic property it presents in blood media, is described under the name of Corynebacterium haemolyticum n. sp. 3. In the present case the origin of the disease cannot be ascribed to another cause but to this germ, as no other one was isolated or observed either in the course of the illness or in the material collected form the corpse. 4. Consulting the medical literature, we have found that similar cases accompanied by a secure bacteriological proof are extremely rare, as only two case are found in which a diphthroid bacterium was isolated from the patients' blood and from the corpse changes of the same, our case appearing in the 3rd place, since 1893. Two other cases are reported with isolation from corpse changes. The cases in which the diphtheroid appears associated with other germs are of a larger number.