Consistently high levels of exhaled nitric oxide in children with asthma. 
Exhaled nitric oxide (eNO) levels in children are unstable because they are regulated by many potent factors.  The purpose of the current study was to evaluate the reliability of eNO levels between a long interval and other lung functions in normal and asthmatic children.  Eighty-three elementary school children (aged 11-12 years; male : female, 39 : 44) participated in this study.  Lung function, airway resistance and eNO levels were measured twice: the first measurement was in autumn 2007, and the second was one year later.  There were 62 non-asthmatic control children (male : female, 31 : 31) and 21 asthmatic children (male : female, 8 : 13).  In both the first and the second examination, the levels of eNO in children with asthma were higher than those in children without asthma.  The parameters of lung function and the respiratory resistance in children without asthma showed a good correlation between the results of the first and second examinations.  The eNO level in non-asthmatic children showed a good correlation between the two.  On the other hand, the peripheral airway parameters of lung function and the respiratory resistance in children with asthma were not correlated between the first and the second examinations.  The eNO level in these patients was well correlated between the two examinations.  These data suggest that the eNO level showed good reproducibility in children with and without asthma.  The eNO level is therefore considered to be a useful marker for reproducibly evaluating a subject's airway condition.