Measurements of nasal nitric oxide (nNO) are attractive because they are completely noninvasive and can easily be performed. The measurements may be useful in the early diagnosis of patients with chronic airway disorders such as Kartager's syndrome and cystic fibrosis. The possible use of nNO measurements in the diagnosis and treatment of allergic rhinitis still needs to be further evaluated because of the variable and also contradicting findings of nNO concentrations in this disease. In this review we will discuss the origin, production and measurement of nNO as well as the effect of allergic rhinitis, nasal allergen challenge and medication on nNO. Subsequently, we examine published data on allergic rhinitis and nNO, and summarize the effect of treatment of rhinitis on nNO. Finally, we discuss the potential future role for nNO in the diagnosis and management of allergic rhinitis.