To compare the clinical efficacy of levocetirizine 5 mg and montelukast 10 mg, administered once daily during two consecutive days, on symptoms of seasonal allergic rhinitis occurring in subjects exposed to ragweed pollen in an environmental exposure unit.

Inclusion Criteria:

• Have had seasonal allergic rhinitis due to Ragweed for the last 2 consecutive years
• Subjects who obtain a minimum sum score, considering SAR related symptoms (mean value), as defined by the protocol

Exclusion Criteria:

• Any clinically significant condition that might interfere with the treatment evaluation, both for efficacy and safety
• Have used forbidden concomitant medications as defined by the protocol