Efficacy, Safety, and Tolerability Study of ACT-129968 in Patients With Seasonal Allergic Rhinitis

Inclusion Criteria * Males and females aged 12-76 years with documented clinical history of symptomatic seasonal allergic rhinitis associated with mountain cedar pollen for the last 2 years. * Evening reflective Total Nasal Symptom Score (p.m.rTNSS) at least 42 out of a maximum potential score of 84 over the 7-day run-in period, or \> or = 6 out of a maximum score of 12 on each of the last 4 consecutive days during the run-in period. Exclusion Criteria * Non-allergic rhinitis. * Severe physical nasal obstruction. * Acute or significant chronic sinusitis. * Bacterial or viral infection of the upper or lower respiratory tract, nasal sinuses, or middle ear. * Ongoing chronic respiratory disorders. * Asthma requiring use of short-acting beta2-agonists \> 2 times a week or any asthma treatment other than inhaled short-acting beta2-agonists. * Diagnosis of aspirin or non-steroidal anti-inflammatory drug (NSAID)-induced asthma. * Nasal biopsy or surgery, sinus surgery, or perforation within the 8 weeks prior to the Screening Visit. * Ocular surgery within the 8 weeks prior to the Screening Visit. * Ocular infections (bacterial or viral) within the 4 weeks before screening. * Use of forbidden medications (prescribed or over-the-counter \[OTC\]) * Congenital or acquired severe immunodeficiency or known Human immunodeficiency virus (HIV)infection.