This will be a double blind, randomised, 4 arm, parallel group, placebo controlled study of three dose levels of OC000459 tablets in patients with asthma controlled by beta agonist drugs alone. This study will compare the patients on OC000459 at three different dose levels (25mg once daily, 100mg twice daily and 200mg once daily) with patients on placebo after dosing for 17 weeks. The trial will be undertaken in an outpatient population. Each treatment arm will consist of at least 110 subjects. The objective is to assess the efficacy of these dose levels on the patients asthma.

Inclusion Criteria:

• Male or female asthmatics, any racial group. Females of childbearing potential must practise two forms of contraception
• Aged 18 to 55 years inclusive.
• Non smokers for at least the past 12 months with a pack history of less than 10 pack years.
• Mild to moderate persistent asthma according to GINA4 guidelines for at least 12 months

Exclusion criteria:

• Receipt of prescribed or over the counter medication within 14 days prior to the first study day