This is a study involving a 2-4 week run-in phase followed by a 12 week double blind treatment phase. During the run-in phase, subjects receive Flixotide®. In the treatment phase subjects will be randomised to one of the two treatment groups and will receive either FlutiForm® and placebo inhaler for symbicort® turbohaler® or symbicort® turbohaler® and placebo inhaler for Flutiform ® . Efficacy will be assessed by lung function tests, asthma symptoms, sleep disturbance due to asthma and rescue medication use. Safety will be assessed by adverse events, lab tests, ECGs and vital signs.