BACKGROUND The preventive use of medications has been proposed to be effective in the treatment of seasonal rhinitis. OBJECTIVE To evaluate the efficacy and safety of mometasone furoate and nedocromil sodium nasal sprays as prophylactic treatment for moderate to severe seasonal allergic rhinitis (SAR). METHODS Sixty-one patients were recruited from 3 referral allergy centers. Inclusion criteria were history of SAR for 2 years or longer, sensitization to relevant local pollen (grasses, Parietaria, and olive), and age older than 12 years. METHODS An open-label, randomized, parallel-group, "real-life" study design was used. Patients received mometasone furoate nasal spray once daily or nedocromil sodium nasal spray 3 times daily starting 2 to 4 weeks before the pollen season and continuing for up to 4 months. Instructions regarding the use of additional medications were given. Diary cards recording symptoms, use of medication, and adverse events were kept by the patients. RESULTS All 61 patients completed the study. The prophylactic use of mometasone furoate vs nedocromil sodium led to significantly more days without symptoms (75.1% vs 54.5%; P < .001). The mometasone furoate group also had lower nasal symptom scores (mean, 1.4 vs 2.9; median, 0 vs 2; P < .001) and was more satisfied (93.1% vs 43.5%; P < .001). No serious adverse event was recorded, and there was no difference between the treatments in any adverse event. CONCLUSIONS Prophylactic administration of mometasone furoate before the pollen season is safe and may lead to improved control of SAR compared with the use of nedocromil sodium.