Isoprostanes are a complex family of compounds produced from arachidonic acid via a free-radical-catalyzed mechanism. They can be quantified as reliable markers of lipid peroxidation. Among the isoprostanes, 15-F(2t)-IsoP and 15-E(2t)-IsoP are biologically active and mediate vasoconstriction and bronchoconstriction and augment nociception. These effects are thought to be mediated via the activation of prostanoid TP receptors, with isoprostanes acting as full or partial agonists. A strong link between lipid peroxidation and diseases associated with ischaemia-reperfusion, atherosclerosis and inflammation has been suggested by elevated levels of F(2)-isoprostanes observed in such diseases. Thus, quantification of F(2)-isoprostanes as a pathophysiological marker provides a unique opportunity to investigate lipid peroxidation in human diseases and provides an interesting biomarker for rational dose selection of antioxidants in diseases where oxidative stress might be involved.