In this review, new knowledge about the potential use of glutamine containing dipeptides as substrates in the frame of parenteral nutrition is presented. Using chemical and biotechnological methods, the stable and highly soluble peptide L-alanyl-L-glutamine (Ala-Gln) can be synthesized in high yields. Studies in experimental rats and dogs demonstrate the effective utilization of intravenously supplied Ala-Gln and the rapid provision of free glutamine for maintenance of the intracellular muscle-free glutamine pool in catabolic situations. Subsequent studies in healthy volunteers provide firm evidence that the infused Ala-Gln is rapidly eliminated from plasma (t1/2:3.8 minutes), associated by a prompt equimolar increase in the concentrations of free alanine and glutamine. Bolus injection and continuous infusion of the peptide was not accompanied by any side effects, and no complaints by the subjects were noted. These results may indicate a safe and efficient use of Ala-Gln as source of free glutamine in parenteral nutrition.