We evaluated the results of essential amino acids supplementation added to a protein restricted diet (0.6 g/kg/day) in patients with advanced renal failure (creatinine clearance under 20 ml/min). A diet containing food with high biologic value was used as control. Diets were tested during 7 months. Anthropometric and nutritional (serum albumin and transferrin) values were normal in both groups both at the beginning and at the end of the treatment period. A slight increase in weight in the natural diet group and in serum phosphorus level in the amino acid supplemented group was observed. Two patients in each group required chronic dialysis, renal function remaining stable in the rest. We conclude that both forms of diet supplementation were effective in preserving nutritional status possibly in delaying deterioration of renal function in patients with advanced renal failure.