Glutathione (GSH) is a major cellular antioxidant, which can conjugate chemically reactive, electrophilic molecules and thus, prevent unwanted reactions with important cell constituents. A large number of electrophilic eicosanoids, in particular alpha/beta-unsaturated ketones, are synthesized during arachidonic acid oxidative metabolism which can participate in the Michael addition reaction with GSH catalyzed by the GSH-S-transferase (GST) family. The structures of these adducts have been determined primarily using mass spectrometry techniques in the past after degradation to volatile products, but more recently by electrospray ionization. GSH-adducts have been observed with molecules synthesized through the 5-lipoxygenase (LTB4, LTC4, and 5-oxo-ETE), 12-lipoxygenase (hepoxilin A3), 15-lipoxygenase (13-oxo-ODE), PGH synthase (PGA1, PGA2, PGD2, PGE2, and PGJ2), and cytochrome P450-epoxygenase (14,15-EET) pathways of arachidonic acid metabolism. It has also been demonstrated that these oxyeicosanoid GSH-adducts do not represent just inactivation products, but they can both retain (GSH-adduct of hepoxilin A3) or show novel biological activities (LTC4 and FOG7).