Objective: The efficacy and tolerability of a new combination inhaler containing both salmeterol 50μg and fluticasone 100μg in a single device was compared with the delivery of the two drugs via two separate inhalers in a multicentre, double-blind, double-dummy study. Patients: 244 symptomatic asthma patients (age range 12 to 78 years) were randomised to a 12-week treatment period with either salmeterol/fluticasone (50/100μg twice daily) via a single inhaler (combination) and placebo twice daily via another, or salmeterol 50μg twice daily via one inhaler and fluticasone 100μg twice daily via another (concurrent). Results: Morning peak expiratory flow rate (PEFR), symptoms and tolerability were collected throughout the treatment period. Adjusted mean improvements in morning PEFR were 42 and 33 L/min for combination and concurrent therapies, respectively, over the 12-week treatment period. Adjusted mean improvements in forced expiratory volume in 1 second (FEV1) from baseline at week 12 were 0.20 and 0.17L for combination and concurrent therapies, respectively. 60% of patients receiving combination inhaler and 64% of those receiving concurrent therapy had a mean daytime symptom score of zero over the treatment period compared with 17 and 15%, respectively, at baseline. Both treatments were well tolerated. Geometric mean morning serum cortisol levels were similar and no differences in the frequency of abnormal results were noted between the two groups. Conclusion: This was the first study reporting the control of asthma by administration of salmeterol and fluticasone in combination via a single inhaler. The new combination inhaler was as effective and well tolerated as the two drugs administered individually and has potential advantages in terms of convenience.