Isoprostanes (IPs) are a recently discovered complex group of stable prostaglandin-like molecules formed by the free radical-catalyzed peroxidation of polyunsaturated fatty acids (1 ). F2 -isoprostanes (F2 -IPs) are formed by the oxidation of arachidonic acid and can be classified into four major regioisomeric groups, and characterized by a cis -oriented side chain (2 ). Because the majority of arachidonic acid is currently esterified in phospholipids, F2 -IPs are initially formed esterified and are subsequently released in the free form following cleavage by phospholipase A2 (3 ). The presence of F2 -IPs in vivo was initially reported by Morrow et al. (1 ). The levels of one of the abundant isomers, 8-epi-PGF2α , was shown to increase by up to 200-fold in established animal models of oxidative injury (4 ). High levels of F2 -IPs can disrupt the physicochemical integrity of cell membranes (3 ), but more importantly can exert significant pharmacological activity. 8-epi-PGF2α is a potent vasoconstrictor acting on the renal, pulmonary, and retinal vasculatures (1 ,5 ,6 ), modulates platelet aggregation (7 ), and is involved in the activation of intracellular signaling (8 ). Isoprostanes can also be formed enzymatically by the cyclooxygenase pathway in platelets, monocytes and vascular smooth muscle (9 –11 ).