IT IS GENERALLY accepted that Sydenham's chorea, or chorea minor, is a manifestation of rheumatic fever. It was only logical, therefore, that McCulloch1 (1938) should use the term "encephalitis rheumatica" for Sydenham's chorea, as had been done before him by Poynton and Paine2 and by Greenfield.8 Greenfield studied the pathologic features of chorea minor in patients who died during the acute stage of the illness. He observed round cell infiltration, consisting of lymphocytes and plasma cells, within the perivascular spaces. More impressive, however, than the infiltration of elements of the blood was the glial reaction of the brain tissue around the perivascular spaces. Sometimes there was present only this spotty glial reaction, which resembles that seen in poliomyelitis and von Economo's (lethargic) encephalitis. There was a great increase in vascularity, with congestion of the capillaries and even subpial hemorrhages. Greenfield expressed the belief that the picture resembled