Evidence indicates that hydrolyzed protein fragments (i.e., peptides) cross the small intestine and reach peripheral tissue via the systemic circulation. Dietary peptides can have specific actions locally, on the gastrointestinal tract, or at more distant sites. These bioactive peptides can alter cellular metabolism and may act as vasoregulators, growth factors, releasing hormones, or neurotransmitters. The available nitrogen choices for enteral nutrition are free amino acids, peptides, or intact proteins. Current experimental evidence indicates that diets that possess the capability of producing luminal peptides are superior to diets lacking this capacity. The parent protein used for enteral nutrition generates specific peptides that can also dictate a variety of metabolic responses. The concept of dietary bioactive peptides offers an explanation for varying effects of diet on physiologic responses. These concepts have spurred research efforts into the possibility of enteral administration of biogenic amines.