1. The anti-elastase composition of bronchoalveolar lavage (BAL) fluid from (α1-proteinase inhibitor (α1PI) deficient and bronchitic patients was determined by immunological and functional assays, together with the cell profile of the BAL fluid.
2. α1PI, anti-leucoprotease and α2-macroglobuin were present in all the samples. BAL fluid α1PI concentrations were significantly lower in the group with serum α1PI deficiency.
3. Lavage fluid from α1PI deficient subjects inhibited less porcine pancreatic elastase than bronchitic BAL fluid (P < 0.005). However, the α1PI was only about 50% active as an inhibitor in both groups.
4. There was no difference in the amount of neutrophil elastase (NE) inhibited per ml of lavage fluid or per mol of the measured inhibitors in the secretions, but both groups inhibited more enzyme than would be expected for these inhibitors (α1PI deficient: median 4.78 mol of NE/mol of known inhibitors, range 0.88–78.80; bronchitic: 1.14, 0.21–4.66), suggesting that an additional inhibitor is present.
5. The total leucocyte and neutrophil counts were elevated (2P < 0.01) in the lavages of α1PI deficient patients, suggesting a greater potential elastase burden than subjects with normal α1PI.