In two patients with chronic renal failure (CRF) different effects of angiotensin convertase inhibitors (ACEI) and angiotensin receptor 1 blockers (AT1B) were observed. In patient 1 with CRF due to hemolytic-uremic syndrome (HUS), with arterial hypertension (HT) and proteinuria, a switch from AT1B to ACEI led to significant deterioration of renal function. After restitution of AT1B, renal function returned to previous range. The 2nd patient with CRF and severe HT, without proteinuria, due to atypical HUS, was on CAPD. Because of severe HT he received 3-4 hypertensives and ACEI in full dose was the main medication. Despite relatively low urea and creatinine values while on dialysis and high residual diuresis several attempts an end of CAPD was unsuccessful because of hyperkalemia and unacceptable increase of urea and creatinine concentrations after few days. Conversion from ACEI to AT1B enabled withholding CAPD, stabilisation of renal function and good control of HT. It seems that in patients with CRF without hyperfiltration syndrome and sensitive to changes in glomerular hemodynamics, in whom blockade of angiotensin action is needed AT1B may be a better option than ACEI. When using ACEI in patients with CRF, it is important to adjust the dose to renal function.