A minimum amount of protein must be supplied to all patients to avoid a catabolic state. If an insufficient amount is given, even excessive non-protein calories will not prevent the catabolism of lean protein stores. However, excessive amino acid (AA) administration can lead to azotemia, hyperammonemia, metabolic acidosis or cholestasis. Protein requirements are substantially higher (per weight) for infants and children compared to adults. The enzyme systems of neonates and infants are poorly developed and cannot appropriately metabolize standard adult AA solutions. Solutions designed for infants are formulated to account for the impaired conversion of methionine to cysteine and subsequently to taurine. Use of these AA solutions results in greater weight gain, improved nitrogen balance and serum AA patterns similar to those of breast-fed infants. The AA solutions used in older children are the same products as those used in adults. For the majority of patients, recommended guidelines for protein requirements should be followed. Ideally 24-32 non-protein calories (NPC) per gram of AA allows for efficient utilization. BUN and acid-base balance must be monitored to assess tolerance for protein administration.