ii) perform genetic association studies for the endpoints of spirometry (FEV1, FVC, FEV1/FVC), PC20 FEV1 for methacholine, and epithelial integrity (Clearance Halftime) for 3 candidate O3 response genes taken from literature searches and/or previously characterized to demonstrate associations. These physiologic endpoints have been examined in terms of both a continuum of response, and discrete "responder" and "non-responder" endpoints.