A patient with severe acute pyonephritis and septicaemia had persistent symptoms of infection despite appropriate chemotherapy. Although no obstruction was seen on ascending ureteropyelography, exploratory lumbar incision was considered. However, computerized tomography (CT scan) failed to show any obstacle or collection of pus but indicated diffuse infection of kidney. Medical treatment was continued and the patient recovered. This case and a review of the literature has prompted the authors to compare CT scan with conventional contrast-radiography methods in septicaemias of renal origin. It appeared that intravenous and ascending uretero-pyelography are often at fault, and the latter is known to carry iatrogenic risks. CT scan is of considerable help when looking for foci of infection and is proposed as a deciding examination in septicaemias with or without signs suggestive of renal lesions.