Interest has focused lately on the potential of anesthetics to protect against oxidant mediated cell damage. Free radicals (such as superoxide radical or hydroxyl radical) are constantly produced as a normal consequence of aerobic metabolism.The discovery of superoxide dismutase (SOD) gave a strong impetus to research in the role of free radicals in human diseases. The term reactive oxygen species (ROS) or oxidants is a collective term that encompasses reactive oxygen metabolites (ROMs) or intermediates (ROIs) including oxygen-derived free radical species as the superoxide anion radicals, hydroxyl and peroxyl radicals and non-radical species such as hydrogen peroxide and hypochlorous acid. The principal antioxidants present in human blood serum or plasma are urate, vitamin-C and E, superoxide dismutase (SOD) and proteins particularly ceruloplasmin, albumin and lactoferrin. Intracellularly, there are in addition the enzymes catalase, SOD, glutathione peroxidase (GPx) and methionine sulfoxide reductase. The interaction of volatile anaesthetics, but not intravenous, with the xanthine oxidase system, as a potential source of oxidant mediated damage, has been implicated. The perioperative period is frequently complicated by hypotension and toxic drug administration; anesthetics are often an additional risk factor for the development of further cell insult and damage.