BECAUSE polymyxin B has significant toxic potentialities its use is sharply circumscribed, and prolonged therapy with it is avoided. This report describes an unusual case in which circumstances necessitated the administration of polymyxin B for almost one year to a patient with a single functioning kidney. Case Report A 3-month-old male infant was admitted to the Pediatric Service, Madigan General Hospital, on May 16, 1956, because of intermittent high fever and vomiting of 6 weeks' duration. On physical examination masses were palpated in both flanks. The urine contained numerous white blood cells and gave a + + + test for . . .