Asthma affects an estimated 300 million people worldwide with a population prevalence of ca 15% in the UK. The WHO has estimated UK disability adjusted life-years per 100,000 population for asthma to be greater than diabetes and breast cancer. Much of this excessive disability is in the 10-20% of patients with asthma which is difficult to control despite currently available therapies. This high morbidity and disproportionate use of health care resources reflects the considerable unmet need in this patient group, and their significance for health care providers.