This paper deals with the discussion of a series of forty-eight cases of acute staphylococcal kidney infection observed and treated at the University Hospital during the past three years. Certain facts concerning the pathology, diagnosis, relationship to secondary invading organisms and treatment that are brought out by these cases are felt to be of particular interest. The cases here reported did not have any apparent preexisting infection of the urinary tract and were uncomplicated by any discernible obstructive lesions. INCIDENCE The staphylococcus is present in a surprisingly high proportion of infections of the urinary tract. Young1found it in 49 per cent of 356 cases studied. Helmholz2found 15 per cent of all cases studied at the Mayo Clinic to be due to some form of the coccus. Kretschmer3found the staphylococcus in 20 per cent of 200 cases uncomplicated by stone, tumor, stricture, prostatic enlargement or