The presence, activities, and molecular forms of the serine proteinases, elastase, and cathepsin G, and their endogenous inhibitors, alpha 1-antitrypsin and alpha 1-antichymotrypsin, were investigated in bronchoalveolar lavage (BAL) fluid of bronchiectasis patients divided into mild, moderate, and severe disease subgroups and compared to BAL fluid from healthy controls. Immunochemical characterization and quantitation were performed by Western immunoblot. The activities of elastase and cathepsin G were recorded spectrophotometrically using synthetic substrates. The results showed a significant difference in elastase and cathepsin G activities in BAL fluid of the three subgroups, revealing the following data--mild subgroup, 0.21 +/- 0.09 mU/g and 57.35 +/- 20.9 U/g; moderate subgroup, 1.87 +/- 1.12 mU/g and 89.24 +/- 31.4 U/g; and severe subgroup, 2.64 +/- 1.63 mU/g and 139.18 +/- 58.3 U/g, respectively--compared to those of the healthy control group, 0.09 +/- 0.03 mU/g and 50.96 +/- 16.5 U/g. Evidently, the protective shield of plasma-derived antiproteinases was sufficient in healthy subjects and, also, in mild cases of bronchiectasis, but not in cases of severe and moderate forms of bronchiectasis, in which free and catalytically active elastase and cathepsin G were detected. The serine proteinases inhibitors (serpins), alpha 1-antitrypsin and alpha 1-antichymotrypsin, have evidently been oxidized and/or proteolytically cleaved in the cases of moderate and severe bronchiectasis. The results indicate that insufficient endogenous downregulation of catalytically active elastase and cathepsin G in BALF leads to tissue injury, resulting in alterative and deformative processes in the bronchiectasis lung.