This was a study to measure the ability of desloratadine and levocetirizine to decrease nasal obstruction in subjects who had study-induced allergic rhinitis. Study participants had allergic rhinitis symptoms induced in a Vienna Challenge Chamber and then received desloratadine or levocetirizine for 8 days. After at least a 10 to 35-day washout period (time when no drug is given), subjects received the opposite treatment for 8 days. Subjects had their total nasal symptom measured.on the 8th day of each treatment period.