Glomerular endothelin (ET1) synthesis is upregulated in chronic renal failure, and urinary ET1 excretion is correlated with disease progression. ET1 antagonists partially preserve renal function and decrease proteinuria independent of the angiotensin tone. Objective 4 of the trial is to assess ET1 turnover before and after start of ACE inhibition, and to evaluate a possible predictive role of ET1 and/or ET1 degrading peptidase excretion for the persistence of proteinuria and disease progression during ACE inhibition and intensified antihypertensive therapy.