The detection of increased levels MMP-9 in acute lung injury (Delclaux et al. 1997; Ricou et al. 1996), idiopathic pulmonary fibrosis (Suga et al. 2000), cystic fibrosis (Delacourt et al. 1995), bronchiectasis (Sepper et al. 1994), and other lung disorders characterizes MMP-9 as a sensitive marker of activation of tissue remodeling after lung injury, but it is unlikely to serve as a indicator of a specific injurious agent or entity in the pathophysiology of many acute and chronic forms of disease. Here, MMP9 is linked to pulmonary fibrosis.