The study will be an open-label, randomised, 3-way cross-over single dose study in 24 healthy subjects to demonstrate dose proportionality of fluticasone furoate (FF) and equivalence of vilanterol (VI) following single dose administration of FF/VI via the novel dry powder inhaler. In each of 3 treatment periods, subjects will receive 4 inhalations of 50/25 mcg, 100/25 mcg, 200/25 mcg FF/VI. Blood samples will be taken for pharmacokinetic analysis and safety (12-lead ECGs, clinical laboratory test, vital signs, adverse events) will be monitored following each dose.