The experience with chronic renal failure in two institutions, a tertiary care referral hospital with a high prevalence of diabetes mellitus and a Veterans Administration Hospital, was utilized to formulate guidelines for the nutritional assessment and therapy of chronic renal failure. For optimal nutritional support of patients with renal failure, it is important to characterize objectively nutritional deficiencies. Thus, dietary history, anthropometric measurements (weight/height ratio, arm muscle circumference, and triceps skinfold), and serum protein measurements (total protein, albumin, and transferrin, in particular) provide valuable data concerning the nutritional status of the patient. The serum urea nitrogen to serum creatinine ratio and urea nitrogen appearance are useful for selecting optimal protein intake. The serum urea nitrogen/creatinine ratio must be interpreted with respect to the factors which influence it; i.e., the urea clearance and the urea nitrogen appearance. The goal of nutritional therapy is the preservation of body cell mass and function, fluid, electrolyte, and acid-base homeostasis, mineral balances, and with early use of dialysis, the avoidance of uremic toxicity. Nutritional therapy, especially in patients with superimposed illnesses and associated anorexia, may be enhanced by the use of formula feedings, tube feedings, and, if necessary, total parenteral nutrition.