In this study, we measured plasma levels of surfactant protein A (SP-A), surfactant protein D (SP-D), matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) in young and middle aged/elderly smokers and in patients with COPD. This evidence concerns the gene MMP9 and chronic obstructive pulmonary disease.