Asthma is a chronic disease, which means that it cannot be cured, but the investigators can use inhalers and tablets to control the symptoms. In asthma, the airways become inflamed and irritated which can cause coughing and make the airways tighten. This 'inflammation' is the root of the problem in asthma. Doctors have different ways to measure the inflammation in the airways. One way is to measure a gas called nitric oxide (NO) on the breath. This is made by the lungs when asthmatic inflammation is present. The investigators have been using NO as a test in research labs for many years, but there are still unanswered questions about how it changes between morning and night and how quickly medicines work on it. In most asthmatics, even small doses of inhaled steroids (preventers) can reduce the NO levels to normal, but in some people this does not seem to happen. The investigators now have portable NO machines that are designed for patients to use in the home. The investigators want to follow NO readings in patients with high levels to measure how they respond to different doses of steroid inhalers. The investigators hope this will help the investigators better understand asthma inflammation and treatments.

Inclusion Criteria:

• Diagnosis os asthma, taking 200-1000mcg budesonide or equivalent per day
• FENO greater than 30ppb on treatment

Exclusion Criteria:

• Recent RTI or prednisolone
• Smoking within 1 year or 10 pack years
• ABPA, COPD, bronchiectasis