Exhaled nitric oxide (eNO) has been proposed as a measure of airway inflammation in children. It is not known, whether children with cough but without wheeze have asthma. Aim: To determine if eNO is associated with airway hyperresponsiveness (AHR), wheeze or cough in atopic children. Methods: 312 atopic children, aged 9-13 years had eNO measured, and had a histamine challenge test. From 245 subjects we obtained questionnaire data about wheeze or cough in the last month. AHR was defined as a dose response ratio (DRR) > 8.1 (% fall FEWmmol+3). Expired air was collected in a 3L wine cask bag and the eNO content measured by chemiluminescent analyser. Results: Exhaled NO correlated significantly with DRR to histamine (r=0.427, p<0.001). No AHR No AHR AHR AHR No Wheeze Wheeze No Wheeze Wheeze N 131 28 54 31 eNO(ppb) 12.32 13.44 17.27* 21.10*# (95%CI) (11.6-13.1) (10.9-16.5) (14.8-20.2) (17.9-24.9) *p<0.0001 compared to normal #p<0.001 compared to No AHR and wheeze In 60 children with wheeze ±cough, eNO was (17.10 (95%CI 14.9-19.6) ppb) significantly higher than in 78 children with neither symptom (13.66 (95%CI 12.2-15.2) ppb, p<0.05), and higher than in 107 children with cough but no wheeze (13.45 (95%CI 12.4-14.5) ppb, p <0.01). There was no significant difference in eNO in asymptomatic children and children with cough. Conclusions: Exhaled NO is related to AHR and distinguishes asymptomatic atopic children from those with asthma. Atopic children with cough only have lower eNO values than those with wheeze (with or without cough), suggesting that they do not have airway inflammation.