Five case reports are used to illustrate that it is possible by computed tomography to differentiate between acute diffuse, acute focal and abscess-forming types of renal infection. In acute diffuse renal inflammatory disease, intravenously injected contrast medium remains in various parts of the renal tissue after an interval of two to six hours following injection. Acute focal inflammatory disease and abscesses produce localised hypodense or isodense lesions. Sequential increase in density following a contrast bolus injection permits the distinction of focal nephritis from an abscess. These findings provides information concerning the type and duration of treatment.