3-D Visualization of the Anti-Obstructive Effect of Levocetirizine

Inclusion Criteria: * Subject must be informed and give written informed consent for study participation * Subject must be able to adhere to dose and visit schedules and meet study requirements * Subject must be aged 18 to 65 (inclusive); gender and race are irrelevant * Subject must have at least a two-year history of allergic rhinitis consistent with persistent allergic rhinitis (defined as symptoms of allergic rhinitis present on four days or more per week or for four or more consecutive weeks per year) * In the previous pollen season, subject must have been sufficiently symptomatic, with a T6SS (reflective) symptoms severity score of at least 10 (out of max. 18). (Symptoms include nasal itching, sneezing, rhinorrhea, congestion, conjunctival itching, redness and tearing graded on a scale of 0 -absent, 1 - mild, 2 - moderate, 3 - severe) * Subject must have a positive skin prick test at screening to one or more allergens in the local panel of seasonal allergens (e.g. grass, tree pollen), but not to perennial allergens. Subject must demonstrate an antigen-induced skin prick wheal of at least 3mm greater in diameter than the diluent control. * Subject must have had a positive nasal allergen challenge within the previous six months. (see \[Riechelmann\]) * Nonsterile or premenopausal female subjects must use a medically accepted method of birth control, e.g. oral contraceptives Exclusion Criteria: * Failure to fulfill all of the above mentioned inclusion criteria * Insufficient ability to understand the nature, scope and possible consequences of the study * Insufficient legal competence or insufficient knowledge of the German language * Participation in another clinical trial within the previous three months * Pregnancy or lactation * Positive skin prick test to frequently occurring perennial allergens, e.g. house dust mites, cats * History of anaphylaxis and/or severe local reactions to skin testing with allergens * Intolerable symptoms that would make participating in the study unbearable, especially the 45 min MRI-session * Any viral inflammation of the upper respiratory system, acute or chronic sinusitis, rhinitis medicamentosa, nasal polyps, clinically relevant anatomic deviations of the nose, active or inactive tuberculosis of the respiratory tract, or asthma other than mild intermittent asthma treated with ß2-agonists on an as-needed basis * Any kind of clinically significant disease, especially any signs of active persistent allergic rhinitis, which would interfere with the study evaluations. * Known intolerance to levocetirizine or any other components of the study drugs * Surgery of the nose or the nasal sinuses within the previous six months * Any deviation from the norm in the physical investigation of any disease which in the investigator's judgment might require impermissible medication, influence study performance and results or affect the patients safety * Intake of drugs which might interfere with the study results * History of alcohol or drug abuse