Hyperkalemia is a severe complication of end-stage renal failure. To evaluate whether ACE inhibitors may even worsen the propensity to develop hyperkalemia in this condition, we have analyzed retrospectively pre-dialytic blood pressure and serum potassium in 15 patients on chronic hemodialysis before and during long-term ACE inhibition. This treatment induced a significant drop in blood pressure (from 173 +/- 3/90 +/- 2 to 159 +/- 5/85 +/- 2 mm Hg [p < 0.05]), whereas serum potassium increased from 4.9 +/- 0.2 to 5.5 +/- 0.2 mM (p < 0.05), irrespective of the dosage of ACE inhibitor and of the residual diuresis. Hyperkalemia was well tolerated and was corrected in all patients by dialysis; treatment was discontinued in only one case. In conclusion, ACE inhibitors represent effective antihypertensive treatment in end-stage renal failure. However, long-term ACE inhibition may be accompanied by a worsening of hyperkalemia, which could be accounted for by a reduced effect of aldosterone on extrarenal potassium homeostasis.