8-Epi PGF2alpha, a potent vasocontrictor, is a specific product of non-enzymatic peroxidation of arachidonic acid. It seems likely that similar products could arise from other polyunsaturated fatty acids (PUFAs) and might be useful biomarkers of their peroxidation in vivo. This was investigated using eicosapentaenoic acid (EPA). EPA liposomes (1 mg/ml PBS) were exposed at 37 degrees C to either 2,2'-azobis-(2-amidinopropane) dichloride (AAPH) or copper ions at final concentrations of 1 mM and 10 microM, respectively. Sample processing involved solid-phase extraction on a C18-followed by an NH2 cartridge. After conversion to pentafluorobenzyl ester/trimethylsilyl derivatives, F3-isoprostanes were analysed by negative ion-chemical ionisation mass spectrometry (GC-MS/NICI) using tetradeuterated PGF2alpha (PGF2-d4) as the internal standard. Quantitative analysis was carried out by selected ion monitoring of the carboxylated anion [M-180] at m/z 567 and 573 for the PGF3-like compounds and PGF2-d4, respectively. EPA oxidised by AAPH or by copper ions gave rise to a family of F3-isoprostanes with 8-epi PGF3alpha as a minor product. Formation of F3-isoprostanes correlated well with other indices of lipid peroxidation (hydroperoxides and thiobarbituric acid reactive substances). The possibility of analysing specific lipid peroxidation products from individual fatty acids should facilitate nutritional and biomedical studies.