Recent reports have suggested that human secretory IgA (sIgA) may have a role in the mediation of atopic disease. We have studied the levels of sIgA, IgA, IgG and IgM in bronchoalveolar lavage (BAL) fluids collected from lungs of healthy non-allergic adults (n = 14), allergic subjects with rhinitis (n = 15), and allergic asthmatics (n = 13), using a panel of monoclonal antibody-based immunoenzymetric assays (IEMAs). In contrast to commercially available immunodiffusion and nephelometric assays, these IEMAs employ highly specific monoclonal antibodies and demonstrate required precision (intra-assay CVs < 17%), parallelism (inter-dilutional CVs < 20%) at minimal detectable immunoglobulin levels in the ng/ml range, and excellent specificity with < 0.1% crossreactivity for heterologous immunoglobulin isotypes. Using these assays, we have observed a significant correlation between sIgA levels and total IgA levels in BAL fluids from all the study patients (r = 0.94; p < 0.01). The percentage of sIgA to total IgA was 84.0 +/- 2.2%. sIgA in BAL fluids from allergic rhinitics (18.0 +/- 2.5 micrograms/ml) and allergic asthmatics (15.5 +/- 2.5 micrograms/ml) were higher than those from nonallergic subjects (10.2 +/- 1.9 micrograms/ml). The only statistically significant difference in sIgA levels was observed in BAL fluids from the rhinitics and nonallergic groups (p = 0.03). Similar differences among the groups were found for levels of total IgA in BAL fluid. There were no significant differences in the levels of IgM and IgG in BAL fluids among the three groups of subjects. We conclude from these results that IgA is the predominant immunoglobulin on the airway surface and that it appears to be produced locally.