Background: Nasal polyps are found in about 5% of asthmatic patients.A close link exists between the upper and lower airways and the concept of the "United Airways" has emerged mainly from studies on allergic rhinitis and asthma. However, other upper airway diseases, such as chronic sinusitis and nasal polyposis may influence lower airway diseases. As for nasal polyposis, eosinophils are the major effector cells in asthma and have been associated with a worsening of this condition.