This study found that sputum MMP-9 concentrations and mRNA expression in COPD are significantly greater than in healthy never-smokers, that sputum MMP-9 concentrations are directly associated with the extent of emphysema measured by CT and that higher MMP-9 expression levels are associated with greater airflow obstruction and reduced diffusing capacity. The gene discussed is MMP9; the disease is pulmonary emphysema.