Based primarily on extrapolation from adult studies, current pediatric asthma guidelines advise the addition of long-acting beta₂-agonists for children symptomatic on low/moderate-dose inhaled corticosteroids before increasing the corticosteroid dose. This study was designed to compare the effect of combination salmeterol/fluticasone propionate (SFC) with doubling the dose of fluticasone propionate (FP) on specific airway resistance (sR(aw)) in moderate/severe persistent asthmatic children. A double-blind, randomized, controlled study was performed; children with asthma (4-11 years old; sR(aw) > 1.3 kPa·s) were randomized after a 2-week run-in (FP, 100 μg, b.i.d.) to either SFC (50 μg/100 μg b.i.d.) or FP (200 μg b.i.d.) via Diskus (GlaxoSmithKline, Stockley Park, U.K.) for 6 weeks. Lung function (sR(aw)-plethysmography and forced expiratory volume in 1 second [FEV₁]) was measured before run-in, at randomization, after 3 weeks, at the end of 6-week treatment, and after 48-hour washout. Symptom scores and rescue medication use were recorded throughout. Thirty-five children entered run-in and 24 were randomized (mean age, 7.3 ± 2.2 years; 50% boys). All children showed an improvement in sR(aw). After adjusting for age, gender, and baseline sR(aw,) children receiving SFC had a significantly greater improvement in sR(aw) compared with those receiving FP (adjusted means ratio [95% confidence interval {CI}], 0.81 [0.68-0.97]; p = 0.021). There was a significant interaction between treatment and gender (sR(aw), adjusted geometric mean [95% CI ]kPa·s, SFC versus FP: boys, 1.25 [1.10-1.41] [n = 7] versus 1.87 [1.61-2.17] [n = 5]; girls, 1.29 [1.10-1.52] [n = 5] versus 1.29 [1.13-1.47] [n = 7]; p = 0.008). There were no differences in FEV₁, symptoms, or rescue medication use between the groups. Addition of salmeterol provides greater improvement in sR(aw) than doubling the dose of FP in children with moderate/severe persistent asthma.