Glucocorticoids block the local allergic response in a variety of ways. However, studies have also shown that glucocorticoids increase in vitro IgE synthesis and that treatment with corticosteroids may result in elevated serum IgE concentrations. The ability of topical glucocorticoids to modulate the mucosal IgE response has not been elucidated. We studied the effect of topical steroid (fluticasone propionate) treatment on the local allergic antibody response induced by challenge with either allergen or diesel exhaust particles (DEP). A parallel group study was performed with ragweed-allergic subjects, each subject serving as his/her own control. Nasal provocation challenges were performed on three groups. One group received ragweed allergen, another diesel exhaust particles, and the third saline. The study was repeated following 1 week of treatment with intranasal fluticasone propionate. Each group received the same challenge as before. The concentrations of total immunoglobulins (IgE, IgG, IgA, and IgM), anti-ragweed antibody, IgE- and IgA-secreting cells, epsilon (epsilon) mRNA, and cytokine mRNAs (IL-2, -4, -5, -6, TNF-alpha, INF-gamma) were measured in nasal lavages performed before and at various time points after challenge. Treatment with fluticasone propionate for 7 days caused a decrease in the concentrations of nasal IgE protein, IgE-producing cells, total epsilon mRNA, and all the cytokine mRNAs tested. Furthermore, treatment with fluticasone propionate inhibited the production of allergen-specific IgE and cytokine mRNAs following challenge with ragweed antigen. However, fluticasone treatment did not significantly inhibit the enhancement of mucosal IgE production or cytokine mRNAs observed following nasal challenge with DEP. These results indicate that 1-week treatment with topical fluticasone propionate was effective in blocking local effects of allergen exposure but was unable to inhibit the adjuvant-like effect of DEP.