Macrophages and monocytes play important proinflammatory roles in allergic inflammation. We hypothesized that these cells would express an activated phenotype in allergic disease of the airways. We therefore compared the expression of 17 activation markers on the surface of alveolar macrophages (AM) and peripheral blood monocytes (PBM) in 13 subjects with asymptomatic allergic asthma (AA), nine subjects with asymptomatic allergic rhinitis (AR), and 11 nonallergic (N). AM were obtained by BAL, and PBM were simultaneously obtained by phlebotomy; both were analyzed for expression of surface markers using a new two-color flow cytometry method that essentially eliminates background autofluorescence. The proportions of AM in BAL fluid from AA, AR, and N subjects were 84 +/- 2, 85 +/- 4, and 91 +/- 1%, respectively; viability always exceeded 92%. Expression of eight markers (CD16, CD18, CD32, CD44, CD71, HLA Class I, HLA DR, and HLA DQ) was significantly (p < 0.05) higher on AM of AA than on N; expression of six markers (CD11a, CD16, CD18, CD71, HLA Class I, and HLA DR) was higher on AM of AR than on N, with differences in CD44 levels approaching statistical significance (p = 0.07). Expression of one marker, CD44, was significantly higher on AM of AA than on those of AR, with differences in HLA Class I levels approaching statistical significance (p = 0.07). In contrast, no significant differences were found among the three groups in the expression in eight other markers (CD11b, CD14, CD23, CD29, CD33, CD35, CD63, and CD64). Finally, similar analysis of PBM from these same subjects failed to find any difference between the three groups in any of the 17 activation markers studied. These data suggest that AM are activated in allergic respiratory diseases, and that levels of HLA Class I and CD44 on AM are altered during allergic inflammation in the upper and lower airways.