Early changes associated with the development of smoking-induced diseases, e.g., COPD and lung cancer (the two commonest causes of death in U.S.) are often characterized by abnormal airway epithelial differentiation. Airway basal cells (BC) are stem/progenitor cells necessary for generation of differentiated airway epithelium. Based on our preliminary observations that epidermal growth factor receptor, known to regulate airway epithelial differentiation, is enriched in BC and its ligand EGF is induced by smoking, we hypothesized that smoking-induced EGF alters the ability of BC to form normally differentiated airway epithelium. To test this, airway BC will be purified using a cell-culture method established in our laboratory and responses to EGF will be analyzed using genome-wide microarrays and an in vitro air-liquid interface model of airway epithelial differentiation.