Therefore, the aim of this study was to determine the immunohistochemical MUC3A and MUC3B expression and mRNA levels by investigating bronchial mucosal biopsies and bronchial brushing samples of large airway epithelium in never-smokers, current smokers with normal lung function, and in COPD patients. The gene discussed is MUC3A; the disease is chronic obstructive pulmonary disease.