Exhaled nitric oxide is the most extensively studied exhaled biomarker. In patients with stable chronic obstructive pulmonary disease exhaled nitric oxide level appears to be normal or only slightly elevated. As exhaled nitric oxide is a good surrogate marker for eosinophilic airway inflammation and eosinophilic inflammation is steroid responsive, patients with elevated exhaled nitric oxide levels may benefit more from a short course of inhaled or systemic corticosteroid treatment. In acute exacerbation most studies report elevated exhaled nitric oxide levels that decrease along with treatment. More importantly, exhaled nitric oxide levels at exacerbation correlate with functional improvements after treatment suggesting the possibility of a role for exhaled nitric oxide in predicting the response to treatment. In conclusion, assessment of airway inflammation using exhaled nitric oxide may identify a subgroup of patients with chronic obstructive pulmonary disease that is likely to benefit from corticosteroid treatment.