Low protein Giovannetti diets in three patients with chronic renal failure have been compared with isonitrogenous, iso-caloric amino acid tablet-substituted regimes. Another patient has been managed on such a regime after regular haemodialysis treatment had to be suspended. The amino acid diets proved palatable and were effective in maintaining nitrogen balance when the caloric supply was adequate. Improved nitrogen balance correlated with diminished faecal nitrogen excretion and falling or stable blood urea levels implying improved urea nitrogen re-utilization. It is suggested that when the caloric supply is adequate for generation of sufficient α-ketonic acid derivatives, ammonia nitrogen is preferentially utilized for the synthesis of non-essential amino acids rather than more urea formation. Metabolic acidosis is a potential hazard of such regimes