Upper airway inflammation is linked to a broad spectrum of disease: nasal polyposis, seasonal and perennial allergic rhinitis, vasomotor or non-allergic rhinitis, and sinusitis. Assessing the degree of upper airway inflammation through objective measures has obvious clinical and research benefits. For example, nasal polyps contain a large number of activated eosinophils - about 20% of the constituents of nasal polyp tissue. Allergic rhinitis is also associated with elevated inflammatory cell counts - eosinophils, basophils, mast cells, lymphocytes and their mediators. The impact of treatment on nasal inflammation is a key factor in the evaluation of new nasal polyp or allergic rhinitis therapies. Therefore it is imperative that nasal inflammation measurements be evaluated for reliability.