Angiotensin converting enzyme (ACE) inhibitors are used widely in the treatment of hypertension and congestive heart failure. An increasing number of patients with chronic renal failure is treated with ACE inhibitors because of their antiproteinuric effect. In patients with diabetic nephropathy ACE inhibitors also slow the progression of renal failure. Direct drug related nephrotoxic effects, like the induction of proteinuria, glucosuria or an interstitial nephritis are rare events. The often observed reduction of the glomerular filtration rate after the induction of an ACE inhibitor therapy is due to the specific intrarenal action of these agents and therefore not an adverse drug reaction.