In a group of 119 patients with advanced chronic renal failure (serum creatinine level 733 +/- 186 mumol/l) the effect of a low-protein diet supplemented with essential amino acids (EAA) or their keto analogues (KA) on uremic metabolism and rehabilitation status was investigated. The protein intake amounted to 0.4 g/kg B.W./day, the phosphorus intake 0.4-0.6 g/day and the energy supply 120-150 kJ/kg B. W./day. In 51 patients there was a substitution with EAA and in 68 patients with their KA. The mean duration of dietary treatment in this study was 19 months (6-64 months). During this time, the serum creatinine increased from 733 +/- 186 to 1,220 +/- 256 mumol/l, whereas the urea nitrogen values remained relatively constant at between 26 and 30 mmol/l. There were no signs of protein malnutrition (nitrogen balance, serum transferrin and serum protein were normal). The hemoglobin concentration remained at greater than 5 mmol/l with creatinine levels of 1,220 +/- 256 mumol/l. During the substitution with KA, there was a significantly greater decrease in serum phosphate (p less than 0.05) and parathyroid hormone (PTH) (p less than 0.01) as compared with the uremics given EAA. In addition, we found a significant increase in testosterone (p less than 0.01) in patients supplemented with KA. Despite advanced chronic renal failure there was a good degree of rehabilitation (full-time work: 21%; part-time work: 66.4%). It can be concluded that a low-protein diet supplemented with EAA or KA can improve the uremic metabolism, rehabilitation status and safely postpone the start of maintenance dialysis.