Although ozone (O3) has been shown to induce inflammation in the lungs of animals, very little is known about its inflammatory effects on humans. In the study, eleven healthy non-smoking males, ages 18-35 were exposed once to 0.4 ppm O3 and once to filtered air for two hours with intermittent exercise. Preliminary results from a study addressing the effect of extended O3 exposure (7 hours, 0.1 ppm) indicated an inflammatory response in the lower airway evidenced by a 4.8-fold increase in the percent of PMN in the BAL. The findings show that an acute exposure to 0.4 ppm O3 as well as an extended exposure result in increased levels of inflammatory cells potentially capable of producing damage in the lower airways of humans.