PCB 126-induced oxidative stress is modulated by green tea extract (GTE) diet supplementation. Plasma F2-isoprostane (A) and metabolite (B) levels were measured by HPLC/MS MS to assess in vivo oxidative stress induced by PCB 126 that is potentially mitigated by GTE supplementation. Relative levels of combined F-2 IsoPs, including PGF2α, 8-iso-PGF2α, iPF2α-III, 8-epiPGF2α, 8-isoprostane, and 15-F2t isoprostanes, were determined by averaging the AUC integration values from retention times of 8 and 11.3 minutes (Q1 = 353.144, Q2 =193.1). Additionally, the level of 13,14-dihydro-15-ketoPGF2α, an F-2 IsoP metabolite, was determined by integrating its peak at 11.3 minutes (Q1 = 355.2, Q2 = 311.4). Data are presented as mean±S.E.M. (n=8–10). GTE supplementation significantly decreased oxidative stress induced by PCB 126 treatment (*p<0.05).