We studied the effect and onset of action of fluticasone propionate aqueous nasal spray (FPANS) on mediator release and eosinophil accumulation in nasal secretions and on nasal symptoms of patients with seasonal allergic rhinitis after nasal allergen challenge (NAC). At the end of the pollen season, 28 patients were randomized in a double-blind and crossover design to receive 7 days' treatment with FPANS (200 µg, once daily) and matching placebo. NACs were performed before and at 6 h and 1, 2, 3, and 7 days during treatment with FPANS or placebo. Nasal secretions were collected for a quantitative determination of mediators and eosinophil count before and 5 min after each challenge. Nasal symptoms were assessed by scales grading the severity of symptoms at the same time. Results showed that for mediator concentrations there was a significant decrease of leukotriene C4(P<0.001) at 7 days after the first administration of FPANS as compared to placebo. Two days after FPANS, both eosinophil counts and eosinophil cationic protein (ECP) concentrations were lower than those of placebo (eosinophils: P=0.032; ECP: P=0.038). The onset became even more important at day 7 (eosinophils;P=0.001; ECP: P=0.009) during the FPANS treatment period. For the subjective nasal symptoms, a significant reduction of symptom scores for nasal obstruction occurred also at day 3 (P=0.017) and for sneezing at day 7 (P=0.003). There was not yet any significant improvement of the objective nasal airway resistance after the different NACs during the study period. In conclusion, this study demonstrated that topical fluticasone propionate is effective in the treatment of mucosal inflammation induced by NAC. For optimal control of nasal symptoms induced by repeated maximal allergen challenges, a treatment period of more than 1 week is required.