The investigators hypothesise that titration of asthma medication against mannitol challenge results will reduce the number of mild asthma exacerbations, in one year, when compared with titration against BTS guidelines. To test this hypothesis the investigators propose a primary care, parallel treatment, patient blinded study in which matched groups of asthmatic patients will be treated in accordance either with BTS guidelines or with our treatment algorithm dependent on mannitol challenge result.

Purpose of the study is to evaluate the efficacy of a treatment algorithm based on the measurement of airway hyperresponsiveness to mannitol challenge, a surrogate marker of airway inflammation, in the long term treatment of asthma in comparison to BTS guidelines.

Inclusion Criteria:

• Male or female asthmatics aged >/= 16 years
• Females must be non pregnant and non lactating
• FEV1 >/= 50% predicted
• Mannitol PD10 \