Papillary necrosis was produced in rats by means of ethyleneimine, and the urographic appearances were studied. At three days and after, there was concentration of the contrast medium in the region of the medulla, resembling that seen in normal animals, despite necrosis and sloughing of this structure. Autopsy radiographs demonstrated that this contrast material lay first within the necrotic medulla and later within the cavity left when it is shed. It is concluded that concentration of the contrast medium by the proximal tubule is sufficient to give this picture and that this should be borne in mind before contrast concentration is equated with urinary concentration by the renal medulla.