1. Repeated injections into rabbits of non-hemolytic streptococci isolated from human cases of infectious endocarditis or rheumatic fever will produce an acute arthritis in the rabbit similar in most respects to the arthritis of acute rheumatism. 2. Microscopical sections of the joints show a gradual transition from an acute exudative inflammation to advanced organization. 3. Endocarditis and pericarditis occur in a small percentage of cases, and focal lesions in the myocardium consisting of necrosis and the infiltration of cells are frequent. These focal lesions differ considerably from Aschoff's submiliary nodules. 4. Lesions in the kidneys and liver occur but are not characteristic. 5. By means of the vital stain it has been shown that the large endothelioid cells which play a prominent part in the joint and myocardial lesions belong to the group of so called macrophages or wandering cells and probably develop from the vascular endothelium.