Study of ACT-129968 in Adult Patients With Seasonal Allergic Rhinitis

Inclusion Criteria: * Males and females aged 18 to 70 years. * Clinical history of symptomatic seasonal allergic rhinitis associated with mountain cedar pollen for the last two years. * Adequate exposure to mountain cedar pollen. * Positive skin prick test to mountain cedar allergen within 12 months of screening. * Sufficient nasal symptom score during a run-in period. Exclusion Criteria: * Non-allergic rhinitis. * Bacterial or viral respiratory tract infection. * Chronic respiratory disorders. * Asthma requiring treatment other than inhaled short-acting Beta2-agonists. * Ocular infections or surgery, nasal obstruction, nasal biopsy or surgery, sinus surgery or perforation. * Smoking within the last year. * Ongoing or recent treatment for seasonal allergic rhinitis. * Initiation of allergen immunotherapy within 6 months of screening.