The following has been established in examinations under optimal conditions: 1. Ultrasound and CT scan appear to be of equal value in respect of validity and significance of information on the nature of findings, especially in connection with spaceoccupying processes, hydronephrosis and pyonephrosis. However, CT supplies a better anatomical and topographical overall view of the situation. 2. CT scanning, is definitely superior in respect of significance of information on the extension and behaviour in respect of neighbouring organs. This is particularly evident in the visualisation of relapses after hyponephromas and in perirenal processes. 3. Computer tomography is clearly superior in the identification of renal aplasias and hypoplasias.