Persistent asthma is associated with airway inflammation, tissue damage, and deposition of extracellular matrix (ECM) proteins, which may be mediated, in part, through release of matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinase-1 (TIMP-1). To investigate the role of allergen in the induction of MMP-9 and TIMP-1, bronchoscopy and segmental bronchoprovocation (SBP) with saline (SAL) and antigen (AG) were performed in 17 allergic subjects. Bronchoalveolar lavage (BAL) was done 5 min and 48 h after challenge and concentrations of MMP-9 and TIMP-1 in BAL fluid (BALF) were measured by ELISA. Forty-eight hours after AG challenge, concentrations of MMP-9 and TIMP-1 were increased in the airway, but not in serum. Zymography demonstrated that MMP-9 was the predominant metalloproteinase and was present in a latent proform. MMP-9 immunoreactivity was associated primarily with neutrophils, and concentrations of MMP-9 in BALF correlated with airway neutrophils and, to a lesser extent, with alveolar macrophages. These data suggest that AG challenge leads to generation of factors, including MMP-9, that may be associated with the initiation of bronchial injury, which may then lead to remodeling in asthma.