The aim of this open study was to evaluate the efficacy and safety of new topical corticosteroid Nasonex (mometasone furoate) in allergic, seasonal rhinitis. The investigations were carried out on 30 patients with proven grass pollen allergy. Nasonex was administered intranasally during the pollen season, in a single dose 200 micrograms. During the 3 subsequent visits nasal and nonnasal symptom (total and individual) scores and patient reaction to the treatment were evaluated. Rhinomanometry and number of eosinophils in nasal smear were calculated before and after the treatment. Complete or marked relief of symptoms was observed in 24 patients, moderate improvement in 4 patients and no positive reaction in 2 cases. Nasonex markedly inhibited eosinophil influx to the nasal mucosa. No adverse reaction was observed during 2-week Nasonex treatment. We conclude that Nasonex aerosol is a very effective and well tolerated drug in the treatment of seasonal allergic rhinitis.