The purpose of this study is to identify the genes in airway epithelial and BAL cells that are differentially expressed following inhalation of house dust mite allergen among study subjects with allergic asthma and normal phenotypes. This approach is designed to identify novel genes associated with both asthma pathogenesis (differentially expressed in the exposure-response study) and asthma susceptibility (genetically associated with asthma in a linkage/association study).