Following up on previous studies demonstrating that lung epithelial DUOX1 mRNA expression is attenuated in active smokers and in patients with COPD (22, 23), we evaluated tissue sections from a previous study cohort of patients with COPD and control subjects at Maastricht University (UM) (28) for protein expression of DUOX1 in the small airways. The gene discussed is DUOX1; the disease is chronic obstructive pulmonary disease.