Captopril renography is a powerful tool for evaluating renovascular hypertension. In this article we examine four different protocols: 99mTc-DTPA, [131I]hippuran with captopril, [131I]hippuran with enalaprilat, and 99mTc-mercaptoacetyltriglycine (MAG3). In our experience, [131I]hippuran renograms are a reliable and reproducible test in patients both with and without azotemia. Although our experience with the new 99mTc-MAG3 technique is somewhat limited, it appears that this will also be a valuable test, which additionally has several advantages over hippuran, namely, a smaller turnaround time between test and baseline study, a smaller dose of radioactivity, better images, and more accurate counts. We look forward to the future development of this technique.