||BACKGROUND: Inhaled, long-acting beta2-agonists or antileukotrienes are alternatives as add-on therapy for asthmatic children taking regular inhaled steroids. Any complementary effects would be relevant to the choice between these alternatives. Exhaled nitric oxide (FeNO) may reflect these effects. OBJECTIVE: To compare the control of FeNO provided by salmeterol or montelukast add-on therapy in asthmatic children undergoing regular maintenance treatment with a daily dose of 400 microg of budesonide. METHODS: The study included children with increased FeNO despite regular treatment with budesonide, 400 microg/d, and normal lung function. Montelukast, 5 mg/d, salmeterol, 50 microg twice daily, or placebo was compared as add-on therapy to budesonide, 400 microg, in a randomized, double-blind, double-dummy, crossover study. RESULTS: Twenty-two children completed the trial. The geometric mean FeNO level was 20 ppb (95% confidence interval [CI], 15-27 ppb) after salmeterol, which was significantly higher than after montelukast (mean, 15 ppb; 95% CI, 11-18 ppb; P = 0.002) and placebo (mean, 15 ppb; 95% CI, 10-21 ppb; P = 0.03). There was no difference in FeNO between the montelukast and placebo groups. Mean forced expiratory volume in 1 second (FEV1) was significantly increased after salmeterol (mean, 2.63 L; 95% CI, 2.34-2.91 L) compared with placebo (mean, 2.48 L; 95% CI, 2.19-2.77 L). Montelukast (mean, 2.57 L; 95% CI, 2.33-2.80 L) was no different than placebo. CONCLUSIONS: The FeNO levels were significantly higher after salmeterol add-on treatment compared with both placebo and montelukast add-on treatment. Salmeterol significantly improved lung function (FEV1) compared with placebo and nonsignificantly compared with montelukast. Montelukast failed to reduce FeNO and improve lung function compared with placebo in this group of children taking regular budesonide, 400 microg.