In previous studies of human nasal polyps and nasal mucosa from subjects with allergic rhinitis, we have demonstrated hematopoietic progenitors, measured as colony-forming units (CFU) in culture, and colony-stimulating activities for basophil/mast cells (BMC) and basophil/eosinophils (Eo). In the present study, conditioned medium (CM) from short-term cultures of nasal mucosal scrapings of subjects with allergic rhinitis are compared with those from normal subjects for colony-stimulating activities, with BMC and Eo CFU in methylcellulose assays of peripheral blood from atopic (N = 6) or nonatopic (N = 6) individuals. CM derived from cultures of nasal mucosal scrapings from subjects with allergic rhinitis stimulated a significantly greater number of BMC/Eo CFU from the peripheral blood of atopic (out-of-season and ragweed-allergic) subjects than from peripheral blood of nonatopic subjects in a series of matched-control experiments (20.6 +/- 4.6 versus 1.9 +/- 0.8; p less than 0.002); in contrast, nasal mucosal CM from normal control subjects did not stimulate an increase in these CFU in peripheral blood from atopic compared to nonatopic subjects. These studies further support the hypothesis that in situ hematopoietic mechanisms are operative in allergic inflammatory reactions and suggest the presence of cells in affected (allergic) epithelium that are "activated" to produce large amounts of BMC and Eo growth and differentiation factors.