F(2)-isoprostanes are derived in vivo principally from the following: (1) the formation of positional peroxyl radicals of arachidonic acid, (2) endocyclization to prostaglandin G(2)-like structures, and (3) reduction to PGF(2)-like compounds. F(2)-isoprostanes have been proposed as biomarkers of lipid peroxidation, oxidative stress status, and the oxidation of low-density lipoprotein (LDL). Using gas chromatography-ion trap-mass spectrometry, we studied how hemodialysis (HD) affects plasma total F(2)-isoprostanes. We examined the plasma total F(2)-isoprostanes in end-stage renal disease (ESRD) patients, before HD, after HD, between HD, and in control subjects. Plasma concentrations of total F(2)-isoprostanes were significantly higher in the after HD ESRD patients than the before hemodialysis ESRD patients (P < 0.05). There is no difference between before HD ESRD patients and normal controls. Moreover, a positive or negative correlation was seen between LDL and plasma total F(2)-isoprostanes (P < 0.001), and between age and plasma total F(2)-isoprostanes (P < 0.001). This study indicates HD treatment may be the major contributor of oxidative stress in ESRD patients.