Diary card recordings: asthma symptoms, PEF recordings and inhaled beta2-agonist use. PEF measurements will be undertaken by patients at home using a mini-Wright peak flow meter (Clement Clarke, Harlow, UK). The best of three measurements will be recorded twice daily (pre-treatment) in the diary. Peak flow variability will be calculated from the difference between the highest and lowest daily reading divided by the mean PEF reading multiplied by 100 (amplitude % mean). The average of 3 of the last 7 days PEF measurements before each visit will be used for analysis.