Most research has focused on tissue levels of GSH, but the difference between GSH needs and availability may be equally important in the extracellular fluids, which bathe cells. GSH is found in all extracellular biological fluids, including plasma, interstitial fluid, cerebrospinal fluid, alveolar lining fluid, saliva, bile, pancreatic fluid, tears, sweat. and urine.12 The concentration of GSH in body fluids can be up to 1,000-fold lower than found in the tissues, yet all cells appear to release GSH, suggesting a universal requirement for extracellular GSH to protect cell surfaces.12 In addition, specific functions of extracellular GSH are well described. Bile has a high content of GSH to support detoxification of reactive chemicals in the lumen of the small intestines13 and to enhance iron absorption.14 Lipid peroxides are toxic species in the diet that are eliminated by supplemental GSH.15 GSH in the lining fluid of the lungs eliminates airborne oxidants and helps maintain fluidity of the mucus lining the airways. Elimination of bacteria by pulmonary macrophages in vitro is stimulated by added GSH, but this experiment has not been done in humans in vivo.16 GSH also protects human lung cells (in vitro) from influenza virus and protects against influenza in mice.17 One should note that controlled, double-blind studies of these effects have not been done in vivo in humans.