Glutathione has been implicated as an important antioxidant in the body's defense against the accumulation of reactive oxygen species (ROS). In critically ill patients, the balance between the production of ROS and the availability of antioxidants may shift to favor proliferation of ROS. This in turn may lead to significant tissue injury. Parenteral nutrition (PN) is a feeding modality often required by critically ill patients. PN solutions do not contain the components needed for endogenous glutathione synthesis and, thus, may reduce antioxidant availability and accentuate ROS damage. Supplementation of PN with nutrients that promote glutathione synthesis may attenuate ROS-induced cell destruction.