This randomised, double-blind, parallel-group, multicentre clinical trial evaluated the efficacy and safety of rupatadine, a new antihistamine with antiplatelet-activating factor (PAF) activity, and cetirizine in the treatment of patients with seasonal allergic rhinitis (SAR). A total 249 patients were randomised to receive rupatadine 10 mg once daily (127 patients) or cetirizine 10 mg (122 patients) for two weeks. The main efficacy variable was the mean total daily symptom score (mTDSS) and was based on the daily subjective assessment of the severity of each rhinitis symptom--nasal (runny nose, sneezing, nasal itching and nasal obstruction) and non-nasal (conjunctival itching, tearing, and pharyngeal itching)--recorded by patients in their diaries. The mTDSS was 0.7 for both treatment groups (intention to treat analysis). In the investigator's global evaluation of efficacy at the seventh day, 93.3% and 83.7% patients in the rupatadine and cetirizine groups, respectively, showed some or great improvement (p = 0.022). In the per protocol analysis (n = 181), runny nose at the seventh day of treatment was absent or mild in 81.1% of patients in the rupatadine group and in 68.6% of patients in the cetirizine group (p = 0.029). In any case statistical significance was not maintained at the second week. Overall, all treatments were well tolerated. Adverse events (AEs) were similar in both treatment groups, i.e. headache, somnolence and fatigue/asthenia as the most often reported. Somnolence was reported in 9.6% and 8.5% of patients treated with rupatadine or cetirizine, respectively. The most reported AEs (67%) were mild in intensity. Our results suggest that rupatadine 10 mg may be a valuable and safe alternative for the symptomatic treatment of SAR.