A multicenter, double-blind, parallel-group, dose-tolerance study was conducted to evaluate the safety of fluticasone propionate aqueous nasal spray, a potent new corticosteroid preparation. Ninety-seven adult patients with moderate to severe seasonal allergic rhinitis during the fall weed season received either placebo or fluticasone propionate in doses of 50, 200, or 800-mu-g twice daily for 4 weeks. Safety evaluations included adrenal function evaluation by morning plasma cortisol concentration, response to ACTH stimulation, and 24-hour urinary free cortisol excretion. There was no evidence of effects on adrenal function at any dose. The severity, nature, and frequency of adverse events were similar across all treatment groups, including placebo. Drug-related adverse events were consistent with local nasal irritation. The groups receiving fluticasone propionate showed greater improvement in nasal symptoms (obstruction, rhinorrhea, sneezing, and itching) than did the placebo group. The results demonstrate that fluticasone propionate aqueous nasal spray is safe in doses up to 1600-mu-g per day and effective in the treatment of seasonal allergic rhinitis.