Parenteral nutrition (PN), applied in the management of a neonate with severe obstructive uropathy, corrected hyperkalemia and metabolic acidosis within a few days. During the PN lasting for 45 days the renal function improved considerably, as judged on the basis of the serum urea nitrogen concentration and creatinine clearance. The pattern of weight gain of the patient resembled that of catch-up growth. Positive metabolic balances were recorded for nitrogen, potassium calcium, and magnesium during the PN. The eight essential amino acids plus histidine were used as nitrogen source, supplemented periodically with L-alanine. An addition to the amino acids of L-arginine brought the serum aminogram round to a more normal one but did not have any measurable effect on the retention of nitrogen. In certain selected cases PN may thus be used as an adjunct in the management of chronic renal insufficiency even in infancy.