The many alterations in amino acid and protein metabolism in renal failure are often poorly defined, and the available data concerning them are usually descriptive. Nonetheless, certain factors play an important role in the altered amino acid and protein metabolism of uremia. These include malnutrition caused by poor nutrient intake, loss of nutrients during dialysis, and abnormal metabolism of nutrients. Other factors include uremic toxins, superimposed catabolic illnesses, endocrine disorders, and the reduced capacity of the failing kidney to synthesize or degrade certain hormones, amino acids, peptides, and small proteins. These aberrations have complex interrelationships which sometimes potentiate each other. It is possible that the administration of sufficient quantities of energy, vitamins, and minerals, as well as the dietary manipulation of protein, amino acid and ketoacid intake may improve the metabolism of amino acids and proteins. Vitamin B6 and zinc have special requirements that may affect protein or amino acid metabolism.