Fluticasone propionate is a new glucocorticosteroid with potent topical activity. In a double-blind, randomized, parallel-group study, 423 adult patients with moderate to severe seasonal allergic rhinitis received placebo or fluticasone propionate aqueous nasal spray at doses of 25, 100, or 400 micrograms twice daily (b.i.d.) for 2 weeks. Efficacy was evaluated by nasal symptom scores, nasal airflow, nasal cytology, and global evaluation. All doses of fluticasone propionate were significantly better than placebo in reducing symptoms of seasonal allergic rhinitis. Patients receiving the largest dose of fluticasone propionate (400 micrograms b.i.d.) had a slightly greater reduction (not significant) in symptom scores than patients receiving the smallest dose (25 micrograms b.i.d.). Symptom improvement was evident within 3 days of treatment. Nasal airflow improved in the groups treated with fluticasone propionate, 100 and 400 micrograms b.i.d. Examination of nasal cytograms revealed a striking decrease in both eosinophils and basophils in all three groups receiving active treatment compared with placebo. There were few adverse events and no treatment-related abnormalities in laboratory assays or evaluations of hypothalamo-pituitary-adrenocortical axis function. Comparison of treatment groups indicated that fluticasone propionate aqueous nasal spray was as safe as placebo at the doses studied.