Bronchiectasis is a chronic, debilitating disease characterised by productive cough, airway inflammation, and repeated respiratory infections. Evidence-based treatments are urgently needed. Nicotinamide, a form of vitamin B3, has been shown in a new study to boost the immune system and substantially enhance the killing of important respiratory bacteria. It offers a potentially simple and cost-effective treatment option for the prevention of infective exacerbations in patients with bronchiectasis. We plan to undertake a large randomised controlled trial of nicotinamide treatment. Several feasibility issues need to be assessed before this clinical trial can be undertaken. The aim of our study is to determine the optimal dose of nicotinamide and the magnitude of the antimicrobial and anti-inflammatory effects. The benefits of nicotinamide treatment are expected to include fewer exacerbations, improved quality of life, improved exercise capacity and lung function, and reduced acute healthcare utilisation and costs.