BACKGROUND The use of intranasally administered corticosteroid sprays is an established treatment option for seasonal allergic rhinitis. METHODS In this double-blind, placebo-controlled, multicenter study, 438 patients with moderate to severe symptoms of seasonal allergic rhinitis were treated for 4 weeks with double-strength beclomethasone dipropionate (BDP) aqueous nasal spray (84 micrograms/spray: BDP-ds), once daily; regular-strength BDP (42 micrograms/spray: BDP-rs), twice daily; high-strength BDP (336 micrograms/spray: BDP-hs), once daily; or placebo. BDP-hs was included as a safety comparison group. All treatments were given as two sprays per nostril. RESULTS Physician-rated nasal symptom scores were significantly improved in all three active treatment groups compared with those of the placebo group within the initial 3 days of treatment. Improvement was maintained throughout the 4-week treatment period. BDP-ds and BDP-rs were equivalent at all time points. The BDP-ds, BDP-rs, and BDP-hs groups had greater numbers of patients with a good or excellent therapeutic response at end point than the placebo group. All treatments were well-tolerated, and no unexpected adverse events were reported. No effects on laboratory evaluations or vital signs were evident for any treatment group. CONCLUSIONS The results of this study show that BDP-ds given once a day and BDP-rs given twice a day in the same total daily dose are comparably safe and effective in the treatment of patients with seasonal allergic rhinitis.