Collagenases in bronchoalveolar lavage fluid (BALF) of patients with bronchiectasis and healthy subjects were characterized using specific functional and immunologic assays. The BAL fluid contained interstitial collagenase and collagenolytic proteinases of bacterial origin. Collagenase activities, obtained after organomercurial activation, correlated with the severity of bronchiectasis. In severe cases, collagenase activities were 3.5x10−7 IU/L/48 h or 4.8x10−6 IU/g/48 h (p<0.01), in moderate ones 1.74x10−7 IU/L/48 h or 3.35x10−6 IU/g/48 h (p<0.05), and in mild cases 0.32x10−7 IU/L/48 h or 0.7x10−6 IU/g/48 h (p<0.05). The corresponding activities in healthy control subjects were 0.08x10−7 IU/L/48 h or 0.13x10−6 IU/g/48 h. The cellular origin of interstitial collagenase was assessed with doxycycline inhibition test utilizing the differential sensitivity of fibroblast-type collagenase/MMP-1 (IC50=280 µM) and neutrophil-type collagenase/MMP-8 (IC50=26 µM) to the anticollagenolytic, nonantimicrobial doxycycline action. Interstitial collagenase, contained in BALF, was totally inhibited by 100 µM of doxycycline. It can therefore be concluded that most of mammalian collagenase presented in inflamed fluid of bronchiectasis originated from neutrophils. The molecular forms of neutrophil-type collagenase/MMP-8 were confirmed and analyzed by Western-blot, which showed evidence of the proteolytic conversion of the latent 85-kD MMP-8 proenzyme species into active 65-kD molecular weight species. These findings strongly suggest involvement of proteolytic activation pathway of proMMP-8, especially in severe and moderate forms of bronchiectasis. Furthermore, collagenolytic proteases of bacterial origins may also participate in tissue destruction of the lung.