Acute renal failure due to angiotensin-converting enzyme inhibitors (ACEI) usually results from a marked fall in renal perfusion pressure in patients with renovascular disease. We report herein one case of acute kidney transplant artery thrombosis in a patient with renovascular hypertension. The thrombosis occurred immediately after a single dose of ACEI for evaluation of a renal transplant artery stenosis by renal scintigraphy. The dramatic fall of arterial pressure observed in our patient probably played an important role in the thrombosis. The risk of the administration of a single dose of ACEI coupled with renal scintigraphy in diagnosing renovascular hypertension is stressed.