Ozone (O₃), a major component of urban air pollution, is a strong oxidizing agent that can cause lung injury and inflammation. In the present study, we investigated the effect of inhalation of O₃ on levels of F₂-isoprostanes in bronchoalveolar lavage fluid (BALF) and on levels of antioxidants in the BALF and plasma of hamsters. Because antioxidants, including urate, ascorbate, GSH, and vitamin E, defend the lungs by reacting with oxidizing agents, we expected to find a decrease in antioxidant levels after O₃exposure. Similarly, we expected an increase in the levels of F₂-isoprostanes, which are lipid peroxidation products. Exposure to 1.0 or 3.0 parts/million (ppm) O₃ for 6 h resulted in an increase in BALF neutrophil numbers, an indicator of acute inflammation, as well as elevation of BALF F₂-isoprostanes. The higher dose of O₃ caused an increase in the BALF level of urate and a decrease in the plasma level of ascorbate, but 1.0 ppm O₃ had no effect on BALF or plasma antioxidant levels. Exposure to 0.12 ppm O₃ had no effect on BALF neutrophils or F₂-isoprostanes nor on BALF and plasma antioxidants. We also investigated the effect of O₃ exposure of hamsters during exercise on F₂-isoprostane and antioxidant levels. We found that exposure to 1.0 ppm O₃ during 1 h of exercise on a laddermill increased BALF levels of F₂-isoprostanes but had no effect on BALF neutrophils or on BALF and plasma antioxidants. These results indicate that O₃ induces inflammation and biomolecule oxidation in the lungs, whereas extracellular antioxidant levels are relatively unchanged.