There Has been considerable discussion about the accuracy and interpretation of the isotope renogram (1–8). Usually, the renogram has been evaluated on the basis of other examinations. Often arteriography has been considered the criterion, but it has been shown that arterial stenoses are not necessarily related to hypertension (3). The Howard test (9) and the excretory urogram are interpreted largely on the basis of comparison of the two sides. In bilateral abnormality these tests indicate only the more severely impaired kidney. This study was undertaken to evaluate the renogram by more definitive criteria, namely, the study of resected tissue and the one-year postoperative follow-up of patients undergoing definitive procedures. The renograms of 52 patients who meet obtained on the day prior to the examination in case contrast material is needed to identify the kidneys accurately. The patient is positioned as he will be for the reno-gram, prone with the head of the table raised 30 degrees. Patients mainta...