UNLABELLED The aim of this study was to evaluate the value of Tc-99m ethylenedicysteine exercise renography in patients with hypertension who were suspicious for renal artery stenosis and compare the results with captopril renography. METHODS Twenty-nine patients with hypertension who were highly suspect for having renal artery stenosis were included in the study. Basal captopril exercise renograms were performed within 1 week in all patients with Tc-99m EC. Exercise was performed with a bicycle ergometer as described in the literature. Interpretations of renograms were made according to the consensus report on angiotensin converting enzyme (ACE) inhibitor renography as high, low, or intermediate probability. The sensitivity, specificity, and positive and negative predictive values were also obtained on both the kidneys and a patient basis. The results were compared with renal angiography in 19 patients. RESULTS Twenty of 29 patients had concordant results with both captopril and exercise studies. All discordant tests were normal with captopril but positive with exercise renograms. Nineteen patients with 38 kidneys were included for statistical data analysis. Nine kidneys, which were either atrophic or abnormal during the basal study, were excluded from the kidney-based analysis. With contrast angiography, 8 patients had renal artery stenosis. When evaluated on a kidney basis, the sensitivity, specificity, and positive and negative predictive values for captopril scans were 87%, 100%, 100%, and 95%, and for the exercise scans were 100%, 90%, 80%, and 100% respectively. When calculated on a patient basis with regard to the captopril scans, the sensitivity, specificity, and positive and negative predictive values were 87%, 81%, 77%, and 88%, and for exercise scans were 100%, 54%, 61%, and 100% respectively. There were 2 false-positive exercise scans that were found to be the result of dilated minor collecting systems and changes in kidney contours as a result of motion during exercise. CONCLUSIONS These results indicate that exercise renography has a similar sensitivity but lower specificity compared with captopril scintigraphy in the diagnosis of renal artery stenosis. Because of the lower specificity, its use in the screening of renovascular hypertension may be limited. Exercise renography may be more useful as an investigative tool for essential hypertension.