Severe renal artery stenosis (RAS) is a relatively uncommon complication following renal transplantation but is a curable cause of hypertension which demands reliable early diagnosis to reduce morbidity, mortality and graft loss. Captopril renography has been used for a number of years as a method of detecting RAS mainly in native kidneys, with only a few studies concerning the transplant situation. Controversy still exists as to the diagnostic accuracy of this test and as to the most appropriate interpretation criteria with which to establish a positive result. This paper reports the evaluation of 26 captopril renography investigations on hypertensive renal transplant patients with a suspected diagnosis of RAS. Each renogram study was correlated with an arteriogram as the 'gold standard' which was undertaken within 28 days of the renography. A sensitivity of 92%, a specificity of 86% and an accuracy of 88% were achieved by including a consideration of the change in perfusion to the kidney between pre- and post-challenge studies. It is concluded that captopril renography is a useful screening test for the detection of transplant renal artery stenosis (TRAS).