The present study investigated the association between reported parental smoking and exhaled nitric oxide fraction (FeNO) in young children.In total, 78 children (24 females, mean age 51.3 weeks) were recruited. Fourteen lived with one smoking parent and eight with two smoking parents. FeNO was measured using the modified single-breath technique.Mean +/- SD FeNO levels were 33.0 +/- 18.9, 38.3 +/- 15.0 and 48.3 +/- 14.7 ppb for children with no, one and two smoking parents, respectively. There was a significant linear trend across the groups and, after controlling for other relevant factors, a significant difference between the groups.In the present study, exposure to environmental tobacco smoke was associated with increased exhaled nitric oxide fraction in young children. Furthermore, there was evidence of a dose-response relationship between childhood exhaled nitric oxide fraction and the number of smoking parents.