The GLND trial is to test the hypothesis that alanyl-glutamine dipeptide (AG)-supplemented parenteral nutrition (AG-PN) improves clinical outcomes in adult surgical intensive care unit (SICU) patients requiring PN after cardiac, vascular or colonic operations. The study will be performed at Emory University Hospital (EUH) and Grady Memorial Hospital (GMH) of the Emory University, Atlanta, GA; University of Colorado Hospital (UCH) of the University of Colorado Health Science Center (UCHSC), Denver, CO; Vanderbilt University Hospital (VUH) of the Vanderbilt University Medical Center, Nashville TN, and The Miriam Hospital (TMH) of Brown University Medical School, Providence RI. Postoperative subjects after coronary-artery bypass grafting (CABG), cardiac valve, vascular or colonic surgery and deemed to require PN and SICU care will receive either standard glutamine (GLN)-free PN (STD-PN) or isocaloric, isonitrogenous AG-PN until enteral feedings are established. Specific Aim 1 will determine whether AG-PN decreases hospital mortality, nosocomial infection and other important indices of morbidity. Specific Aim 2 will obtain mechanistically relevant observational data in the Aim 1 subjects on whether AG-PN a) increases serial blood concentrations of glutathione (GSH), heat shock proteins (HSP)-70 and -27, and glutamine; b) decreases the serum presence of the bacterial products flagellin and lipopolysaccharide (LPS) and the adaptive immune response to these mediators; and c) improves key indices of innate and adaptive immunity. This study is designed to delineate the clinical benefit of a major new nutrition support strategy in high-risk SICU patients.