Bacterial infections of the urinary tract now constitute a large percentage of the refractory infections encountered in clinical medicine and represent one of the greatest challenges facing physicians today. Satisfactory information regarding the incidence, pathogenesis, natural history, and management of pyelonephritis is lamentably lacking. Chronic infection of the urinary tract—particularly pyelonephritis—is frequently difficult to diagnose and more difficult to control; the risk of relapses is high, in spite of intensive therapy over a long period of time, and the course of the disease may be one of slow, steady progression leading to hypertension, uremia, renal dwarfism, or all three.1,2Much suffering and early death are the consequences of chronic pyelonephritis in many children. Relapse of the infection or reinfection in a kidney that has once been damaged is very common, and may appear soon after cessation of therapy, even when the urine has been free from bacteria and the