The use of nonsteroidal anti-inflammatory drugs is associated with an incidence of severe gastrointestinal adverse events of 2-4%, the most common of which is bleeding. These events are largely attributable to the ability of these drugs to suppress prostaglandin and thromboxane synthesis. Prostaglandins perform a number of important functions in the gastrointestinal tract, particularly with respect to resistance of the mucosa to injury. Nitric oxide also appears to be a key mediator of gastrointestinal mucosal defence, and this has been exploited in the development of a novel class of anti-inflammatory drugs, called "NO-NSAIDs", which exhibit little if any gastrointestinal toxicity. NO-NSAIDs are more effective than traditional NSAIDs in reducing pain and inflammation. Another class of inflammatory mediators that contribute to gastrointestinal mucosal defence are the lipoxins. These products of arachidonic acid metabolism can increase the resistance of the stomach to the damaging effects of aspirin. Indeed, aspirin can trigger the formation of a lipoxin by the stomach which acts to diminish the damaging effects of this drug. Lipoxins and nitric oxide are important mediators of mucosal defence in the stomach (and elsewhere in the gastrointestinal tract) and represent attractive therapeutic targets for reducing the incidence of gastric ulceration.