A low-protein, low-phosphorus diet supplemented with essential amino acids and keto analogues was given to 12 rats, starting from the 90th day after subtotal nephrectomy. The purpose was to assess its effect on the residual renal function and on the nutritional status in rats with already established severe renal failure. Ten control rats in the same conditions, following a standard diet supplying normal amounts of protein and phosphorus were also studied. The supplemented diet exerted a well-evident protection of residual renal function and structure: lower rate of decline of creatinine clearance, lower mortality, significant decrease of proteinuria and almost total absence of histological signs of activity. The nutritional status was also well protected by the dietary therapy: increase of body weight, normal values of total serum protein, and low-constant values of urea appearance. In the control rats body weight decreased, total serum protein was lower than normal and the values of urea appearance were increasing simultaneously with a decreasing food intake and body weight.