We found no significant differences between patients with stable mild/moderate COPD and control subjects (including smokers with normal lung function) in SMAD2, SMAD3, SMAD6, and SMAD7 expression and localization in the lower airways, confirming previous studies.23, 37, 38 In contrast, reduced SMAD6 and SMAD7 mRNA expression was reported in bronchial biopsy samples from patients with stable COPD,39 as well as decreased SMAD7 mRNA in the bronchial epithelium40 and decreased SMAD mRNA expression41 and SMAD protein expression in the peripheral lung.42 Here, SMAD3 is linked to chronic obstructive pulmonary disease.