The low-protein diet (LPD) is used in patients with advanced chronic renal failure (CRF) to improve their symptoms and decrease the progression of CRF. LPD entails the risk for caloric malnutrition, which increases protein catabolism. Two groups were obtained from a total of 33 patients with CRF with LPD (0.6 g protein/kg/day): control group (group C), which went on with the same diet, and a group S, in which a portion of proteins and calories were provided through a low-protein and hypercaloric supplement (Suplena). During 6 months the protein intake and the evolution of the nutritional status and renal function were studied and compared between both groups. Additionally, tolerance and secondary effects of the supplement were studied in group S. Twenty-two patients (eleven in each group) completed the six month follow-up. At the end of the study, group S had the nutritional parameters better preserved, came closer to the low-protein diet objective, had a better compliance with therapy and had a less marked decrease in renal function--as measured by creatinine clearance--than group C. Tolerance to supplement was good in more than 70% of patients and secondary effects--nausea, vomiting and loss of appetite--occurred in 18% of patients at the end of the 6 months. We conclude that the use of this supplement in an LPD is usually well tolerated, enhances the compliance with the diet and can be of benefit for the mebacolic-nutritional status.