OBJECTIVES Chronic rhinosinusitis with nasal polyposis (CRSwNP) and asthma share characteristic inflammatory features and histopathologic findings of airway remodeling. Remodeling, which is controlled by matrix metalloproteinases (MMP), is a key event in the pathogenesis of asthma. The MMP functions have rarely been evaluated in CRSwNP. STUDY DESIGN Prospective and in vivo. METHODS MMP-7, MMP-8, MMP-9, and tissue inhibitor of metalloproteinase (TIMP)-1 concentrations were analyzed by enzyme-linked immunosorbent assay and their molecular forms by Western immunoblotting and gelatin zymography in 24 patients operated on for CRSwNP and in nasal lavages from 19 healthy controls. MMP function, protective or destructive, was evaluated by comparing MMP/TIMP-1 levels with the disease activity, estimated by tissue eosinophilia and a need for re-operations. RESULTS Significantly increased levels of MMP-8/TIMP-1 and MMP-9/TIMP-1 were found in patients without tissue eosinophilia relative to eosinophil-positive CRSwNP patients and controls, as well as in patients who did not require re-operation in comparison with re-operated patients. In eosinophil-positive and re-operated patients, these parameters were within the same range than in controls. CONCLUSIONS Proteolytic spectrum is different in eosinophilic and noneosinophilic CRSwNP, suggesting a new mechanism for eosinophil accumulation in the disease pathogenesis. Enhanced MMP-8 and MMP-9 expression was associated with a better prognosis/clinical outcome, and thus these results may represent a synergic, protective role of MMP-8 and MMP-9 in host response in CRSwNP. Because synthetic MMP inhibitors, capable of equilibrating the unfavorable MMP/TIMP-ratio, may be of potential therapeutic value in chronic respiratory tract diseases, the MMP functions in inflammatory conditions need to be carefully established.