The N(2) slope is an index of inhomogeneous distribution of ventilation and has been suggested to be suited for early testing of chronic obstructive pulmonary disease (COPD) in smokers. The aim of the present study was to examine the association between the fraction of exhaled nitric oxide (FENO) and the N(2) slope in a random population of smoking and non-smoking men. Altogether 57 subjects were included in the study, 24 never-smokers, seven ex-smokers and 26 current smokers. Subjects were examined twice, in 1995 when they regarded themselves as healthy, and in a follow-up in 2001. Spirometry, N(2) slope and high-resolution computed tomography (HRCT) were performed in 1995 while the follow-up examination included also measurement of FENO. The FENO value was significantly lower and the N(2) slope higher in current smokers. In smokers but not in never- or ex-smokers FENO was correlated to the difference in N(2) slope between 1995 and 2001 (r(s)=0.49, P=0.01). We analysed the data by multiple linear regression adjusted for smoking, mild respiratory symptoms and inhaled steroids. There were significant associations between FENO and the N(2) slope both in 1995 and in 2001. The strongest association was found to exist with the change in N(2) slope during these years. Sixteen of the subjects could be classified as having COPD, six with mild and ten with moderate COPD. There was a trend for an increase in N(2) slope with increased severity of COPD; among subjects with no COPD the N(2) slope in 2001 was 2.3% N(2)/L, and those with mild and moderate COPD had 2.5% N(2)/L and 3.9% N(2)/L, respectively (P=0.0004). No such trend was seen for FENO (17.8, 15.5 and 20.3 parts per billion (ppb), respectively, P=0.8). The results show that FENO is associated with the N(2) slope, indicating that FENO reflects inflammatory changes in the peripheral airways of both non-smoking and smoking subjects.