Protein metabolism in uraemia is reviewed. Very few, if any, disorders of amino acid metabolism can at present confidently be attributed to uraemia per se rather than to protein/energy deprivation. Retained urea nitrogen is recycled to the liver as ammonia; a proportion is reutilized for synthesis of non-essential amino acids and, if their carbon skeletons are supplied, for synthesis of essential amino acids. Practical applications of the reutilization of non-amino nitrogen in advanced chronic renal failure are being explored. Nevertheless, uraemic individuals readily become undernourished, and they should receive as much protein as their symptoms will permit.