Dietary energy requirements were evaluated during 16 studies that were carried out in six clinically stable nondialyzed chronically uremic patients who lived in a clinical research center and were fed diets providing 45, 35, 25 or 15 kcal/kg/day. Each diet was fed for 23.7 +/- 5.7 SD days and provided about 0.55 to 0.60 g protein/kg/day. Nitrogen balance after equilibration and adjusted for changes in body urea nitrogen, and change in body weight each correlated directly with energy intake. Correcting for estimated unmeasured nitrogen losses of about 0.58 g/day, nitrogen balance was negative in one of four patients fed 45 kcal/kg/day, one of five patients receiving 35 kcal/kg/day, three of five patients ingesting 25 kcal/kg/day and both patients fed 15 kcal/kg/day. The urea nitrogen appearance (UNA), the UNA divided by nitrogen intake, and several plasma amino acids, determined after an overnight fast, each correlated inversely with dietary energy intake. Resting energy expenditure measured by indirect calorimetry did not differ from normal and averaged 0.012 +/- 0.0033 kcal/kg/min with the different diets. These observations suggest that although some clinically stable nondialyzed chronically uremic patients ingesting 0.55 to 0.60 g protein/kg/day may maintain nitrogen balance with energy intakes below 30 kcal/kg/day, a dietary intake providing approximately 35 kcal/kg/day may be more likely to maintain neutral or positive nitrogen balance, maintain or increase body mass, and reduce net urea generation.