Payne and co-workers describe the identification of different subgroups of paediatric asthma based on airway nitric oxide (NO) concentrations. A group of asthmatic subjects who remained symptomatic after 2 weeks of treatment with oral prednisolone included both patients who continued to have raised NO concentrations and patients with normal NO concentrations before and after prednisolone.1 Since airway NO concentrations are believed to reflect airway inflammation in asthma, the authors conclude that their findings: “ . . .suggest a different basis for symptoms between the two subgroups, with inflammation playing a less important role in those patients with normal NO levels”.

The current understanding of increased exhaled NO concentrations in asthma is based on the assumption that constitutive NO synthase (NOS) derived …