Data processing and analysis: The primary analysis is a comparison between treatments of morning PEF. Secondary endpoints include: symptom scores, exacerbation rates, spirometry, airway responsiveness to methacholine, sputum cell counts, eNO and immunological tests in blood. The main analyses will be carried out by Normal Linear Models that include parameters for patient, period and treatment. Some variables may be unsuitable for this, in which case the within-patient treatment differences will be calculated and then analysed by either t-tests or Wilcoxon tests, as appropriate.