We evaluated 9 patients with transplant renal artery stenosis. Captopril treatment always resulted in a dramatic decrease in renal function. Moreover, only in patients (n = 2) with a stenosis in one out of more renal arteries a satisfying fall in blood pressure was achieved. Surgical reconstruction of the stenosis was successful in 4 out of 5 patients. Angiotensin I-converting enzyme inhibition in transplant renal artery stenosis often leads to loss of graft function, probably due to efferent vasodilation.