The metabolic effects of intravenous peptides have undergone extensive investigation in recent years. Dipeptide solutions provide a mechanism for the provision of selected amino acids that may be conditionally indispensable under certain clinical conditions. In particular, amino acids such as cystine, glutamine, and tyrosine may be difficult to provide in their free form, but their availability can be increased substantially when they are supplied in the form of a dipeptide. Animal and human studies have demonstrated that parenteral dipeptides are cleared rapidly from the plasma compartment and favorably influence nitrogen equilibrium in healthy volunteers and catabolic patients. Certain dipeptides offer the potential for tailoring tissue-specific nutrition therapy. It seems likely that parenteral peptides will offer a major change in the delivery of intravenous nutrients.