The recent ARIA (Allergic Rhinitis and its Impact on Asthma) project has generated interest in simultaneous involvement of the lower respiratory airway in cases of chronic rhinosinusitis and allergic rhinitis. This study takes into account the extent of pulmonary function involvement in these patients. Relevant indicators of pulmonary function were assessed in 203 patients with chronic rhinosinusitis who were scheduled to undergo FESS because of failed medical treatment. These were divided into two groups, with and without nasal polyps. Another 89 patients with allergic rhinitis participated in this study. In all these patients there was no obvious or diagnosed lower respiratory involvement such as asthma or chronic obstructive pulmonary disease (COPD). Prior to FESS an extensive range of pulmonary function tests were performed along with rhinomanometry, and the radiographic severity of chronic sinusitis was assessed by the Lund-Mackay CT staging system. IgE levels were measured along with inflammatory mediators and exhaled nitric oxide concentration. The results showed that pulmonary function was significantly affected in chronic rhinosinusitis patients compared with normal controls but the presence or absence of polyps did not matter. Pulmonary function parameters did not seem impaired in patients with allergic rhinitis as compared with controls, and the same was the case regarding nasal obstruction between patients with chronic rhinosinusitis and controls. In patients with chronic rhinusinusitis, variations in CT scores according to the Lund-Mackay scoring system and IgE levels did not relate to the presence of nasal polyps. However, a higher level of IL-5 significantly correlated with reduced pulmonary function. The authors claim that this study has shown for the first time that patients with chronic sinusitis have latent obstruction of the small airways, as detected by pulmonary airflow testing, even though these patients may not be diagnosed as having obstructive lung function changes and tend to be asymptomatic. It has been suggested that cytokines and chemokines present in the post-nasal discharge are important factors causing asthma and COPD. The study is well controlled and subjected to statistical analysis. It adds an important dimension to the concept of ARIA.