Asthma is a fluctuating disorder characterised by intermittent exacerbations which are inconvenient and sometimes frightening for patients and frequently require medical intervention and treatment with oral corticosteroids. The British Asthma Guidelines recommend a doubling of inhaled steroid dose at the first sign of an exacerbation but the effectiveness of this has never been studied in a controlled trial. This project will determine the ability of monitoring peak flow and asthma symptoms to predict a subsequent exacerbation requiring treatment with oral corticosteroids and the efficacy of patients doubling their inhaled steroid dose as a means of preventing the need for oral corticosteroids.