This is a study of GW642444M, a long-acting beta 2 specific agonist. This study will examine GW642444M via the inhaled route and will assess the efficacy, safety, tolerability, pharmacodynamics and pharmacokinetics of a single administration of three inhaled doses (25, 100 and 400 µg) of GW642444M in persistent asthmatics. This study will be a single-centre, placebo-controlled, dose-ascending, five-way crossover in 30 asthmatic patients.