The goals of the research are designed to accomplish genetic association studies of candidate genes in healthy normal individuals exposed to 0.2 ppm for 2.25 hours with intermittent exercise in order to search for associations between defined genotypes/haplotypes and 3 specific in vivo respiratory endpoints: a) change in FEV1 immediately after ozone exposure; b) change nonspecific bronchial reactivity as reflected in the change in methacholine PC20 FEV1 24 hours after ozone exposure ; and c) change in lung epithelial integrity as reflected in the Clearance Halftime of technetium 24 hours after ozone exposure. These studies have been carried forward to take place in 4 phases: