A multicenter double-blind, randomized, parallel group study was conducted to evaluate the once daily administration of fluticasone propionate, a potent, new corticosteroid preparation, for the treatment of seasonal allergic rhinitis. Adult patients (n = 227) were treated for 2 weeks with fluticasone propionate aqueous nasal spray 200 micrograms QD or 100 micrograms BID or matching placebo during the autumn pollen season. Overall, the administration of fluticasone propionate once daily in the morning was as effective as the twice daily dosage regimen, and either regimen was more effective than placebo. Improvement in clinician-rated and patient-rated nasal symptom scores, including morning nasal obstruction, was evident within three days of fluticasone propionate therapy and continued throughout the treatment period. Fewer patients receiving fluticasone propionate used rescue medication and had nasal eosinophilia compared with patients receiving placebo. Adverse events were similar in frequency and nature in all three treatment groups. Morning plasma cortisol concentrations and response to cosyntropin stimulation were similar across groups and offered no evidence of HPA axis suppression. We conclude that fluticasone propionate aqueous nasal spray administered once daily is a safe and effective treatment for seasonal allergic rhinitis. The convenience of a once daily regimen may encourage better compliance.