This review briefly explains the basic facts about nitric oxide, which is entering clinical practice as a measure of lower airways inflammation and is likely also to be employed in otorhinolaryngological practice.These include the validity of nasal nitric oxide in diagnosing primary ciliary dyskinesia and in monitoring the response to chronic rhinosinusitis therapy. The nasal nitric oxide value combined with a humming manoeuvre, which increases the passage of nitric oxide from the sinuses to the nose if the ostiomeatal complex is patent, could reduce the need for computed tomography scans. The link between nitric oxide production and ciliary beating requires further exploration. Therapeutic adjustments to nitric oxide production are under investigation.Nitric oxide is likely to prove highly relevant to airways defence, as well as being an inflammatory mediator. Nasal nitric oxide probably explains some of the benefit of nasal rather than mouth breathing.