MMP-9 (gelatinase B) has been implicated in the pathogenesis of asthma (Cataldo et al. 2000), idiopathic pulmonary fibrosis (Fukuda et al. 1998), chronic obstructive pulmonary disease (COPD; Russell et al. 2002), and acute lung injury (Lanchou et al. 2003). Here, MMP9 is linked to chronic obstructive pulmonary disease.