This study was designed to measure symptoms, IL-4, IL-5, IFN-gamma, and eosinophilic cationic protein (ECP) in nasal secretions from subjects experiencing an artificial allergy season and to look for evidence of priming. Clinically relevant allergen was administered intranasally out of season to 12 asymptomatic individuals with seasonal allergic rhinitis. These individuals were then randomized to receive allergen or saline daily for the next 7 days. Nasal secretions and scrapings of nasal epithelium were obtained at baseline (day 1), 24 hours after the initial allergen administration (day 2), and 24 hours after the last instillation of allergen or saline (day 9). Nasal symptom scores (p < 0.0002), IL-5 mRNA (p= 0.03), and ECP (p < 0.02) increased after receiving the first challenge (day 2 compared with day 1). In the six subjects randomized to receive seven sequential daily challenges with allergen, symptom scores remained elevated (p < 0.02), IL-5 protein increased (p= 0.02), and IFN-gamma (p= 0.02) levels decreased (day 9 compared with day 1). In the six subjects randomized to receive seven sequential daily challenges with placebo, symptom scores, IL-5, and IFN-gamma levels were not significantly different (day 9 compared with day 1). Compared with the findings at day 2 (n= 12), the treated subjects (n= 6) had no further increase in symptoms but did show a further increase in IL-5 (p= 0.01) and a decrease in IFN-gamma (p= 0.02) at day 9. Daily instillation of moderate doses of allergen intranasally is characterized by persistent symptoms, elevation of IL-5, and reduced levels of IFN-gamma.