Growth outcomes for extremely premature infants remain poor, and improving growth in this population will require a better understanding of how to limit proteolysis and promote protein accretion. Extremely premature infants exhibit high rates of proteolysis that are unrestrained by physiologic increases in insulin, intravenous amino acids, and full parenteral nutrition. Imbalances in current amino acid solutions may be in part responsible for the inability of parenteral nutrition to reduce proteolysis in preterm infants. However, amino acids in parenteral nutrition are effective for increasing protein synthesis in extremely preterm infants, which leads to improved protein balance. Current evidence suggests that early administration of 3 g amino acids · kg−1 · d−1 to extremely premature infants is safe and effective. Enteral nutrition may be more effective than parenteral nutrition in limiting proteolysis and producing protein accretion in preterm infants, but the protein content of current preterm formulas may be inadequate for supporting optimal growth in this population. Important areas of future research include determining whether altered intravenous amino acid solutions can better effect reductions in proteolysis, investigating the effect of enteral nutrition on proteolysis and protein accretion, and conducting a large randomized controlled trial of formula with a higher protein content. Am J Clin Nutr 2007;85(suppl):621S-4S.