27 patients with creatinine clearances ranging from 20 to 2 ml/min were treated daily with 6.9 mg/kg of muzolimine, for 10 to 25 days. The hyperhydration state with oedema decreased gradually in all patients without hypotensive phenomena. Muzolimine benefited hypertension in patients with expansion of the extracellular space and it also strengthened the effect of clonidine or minoxidil. Important diuretic and natriuretic effects were obtained. Metabolic acidosis improved. No subjective adverse reactions to the drug or side effects were noted. High-dose muzolimine appears to be efficacious and safe for short-term treatment in patients with severe chronic renal failure.