Treatment of kidney transplant recipients with inhibitors of angiotensin-converting enzyme (iACE) is associated with increased risk of deterioration of renal function. Between 1988-1992 in Transplantation Institute, 71 renal allograft recipients were treated with iACE. 44 of them received iACE in order to reduce proteinuria, 18 due to secondary polycythemia and 9 recipients received iACE because of hypertension resistant to at least 3 hypotensive drugs. Acute renal failure developed in 5 patients and all of them received iACE as treatment of resistant hypertension. After resumption of renal function, in 3 of 5 patients artery stenosis of the transplanted kidney was found. In 1 recipient acute renal failure occurred despite normal renal arteriography and normal indexes of the flow through renal arteries determined by Doppler ultrasound examination. In 2 patients acute renal failure appeared after a single minimal dose of iACE. Severe arterial hypertension in patients with transplanted kidney is a particular risk factor for development of acute renal failure after iACE. The normal arteriography in transplanted kidney and normal arterial blood flow measured by means of Doppler ultrasound do not exclude the possibility of development of acute renal failure after iACE.