It determinates an inflamatory reaction of the renal pelvis, the renal chalices and principally the interstital tissue of the kidney, with lesion on the tubular system and glomerular lesions.The processes are shown on acute or chronic ways.In the acute cases, the therapy is simple and effective,but when the disease becomes chronic ,it`s proteiform and simulator.The diagnosis is stated only in advanced stages of the lesions, such as chronic insuffienciy of the kidneys and maligant hypertension.In some cases the processes are diagnosed in the autopsy.The pyelonephritis constitute the most insidious of the renal affections.When it`s chronic it`s responsiple for the majority of the death cases by insuffienciy of the kidneys