This study reports the effects of a low-protein, low-phosphorus, supplemented diet in 8 type 1 diabetics with renal failure. The rate of decline of creatinine clearance, the changes of the urinary protein loss, of total serum protein, of the daily insulin requirement, of the nutritional status and of some hormonal derangements were examined. The rate of decline of creatinine clearance decreased from 1.38 +/- 0.27 ml/min/month during a previous 15.9-month period of unrestricted protein diet, to 0.03 +/- 0.37 ml/min/month during the 17.4 months on supplemented diet. Urinary protein loss significantly decreased, and total serum protein increased. The daily insulin requirement decreased and no deterioration of the nutritional status occurred. Secondary hyperparathyroidism was partially reversed and the mild hypothyroidism corrected. A restricted protein and phosphorus diet supplemented with essential amino acids and ketoanalogs seems to exert several beneficial and no unwanted side effects in type 1 diabetics with renal failure.