The anti-elastase composition of bronchoalveolar lavage (BAL) fluid from alpha 1-proteinase inhibitor (alpha 1PI) deficient and bronchitic patients was determined by immunological and functional assays, together with the cell profile of the BAL fluid. alpha 1PI, anti-leucoprotease and alpha 2-macroglobulin were present in all the samples BAL fluid alpha 1PI concentrations were significantly lower in the group with serum alpha 1PI deficiency. Lavage fluid from alpha 1PI deficient subjects inhibited less porcine pancreatic elastase than bronchitic BAL fluid (P less than 0.005). However, the alpha 1PI was only about 50% active as an inhibitor in both groups. 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 (alpha 1PI 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. The total leucocyte and neutrophil counts were elevated (2P less than 0.01) in the lavages of alpha 1PI deficient patients, suggesting a greater potential elastase burden than subjects with normal alpha 1PI.