Intracellular oxidation and reduction (redox state) correspond closely to the surrounding environment. Most environmental factors affecting this balances such as oxidants, ultraviolet light, radioactive emissions, infections, and allergic reactions represent oxidative stress upon cells. We examined intracellular redox state after oxidative stress upon cultured human airway epithelial cells (Calu-3) by measuring reduced (GSH) or oxidized (GSSG) glutathione. We studied cytokine production, which is related to glutathione redox regulation, in response to ozone and also evaluated the effect of pretreatment with an ethyl ester of reduced glutathione (GSH-OEt) on cytokines. Ozone exposure (3.0 ppm, 3 min) time-dependently changed the redox state, while increasing production of interleukin(IL)-8 and IL-6, mRNA and protein. Treatment with GSH-OEt before ozone suppressed IL-8, but stimulated IL-6 production. Thus, oxidative stress affects intracellular glutathione redox state, in airway epithelial cells, activating signals to increase production of cytokine, modulation that may exacerbate respiratory symptoms.