Gastro-oesophageal reflux (GOR) has been found to be prevalent in children with cystic fibrosis (CF)and may further worsen lung damage via reflex bronchospasm or pulmonary aspiration. Chest physiotherapy may result in increased episodes of GOR as demonstrated in children. Lung transplantation may worsen pre-existing GOR. This study will determine the prevalence, severity and significance of symptomatic and silent GOR in adults with CF before and after lung transplant using 24hr oesophageal pH monitoring, a valid symptom questionnaire, quality of life questionnaires and gastric emptying studies. This study will identify the extent of GOR in a large adult CF population and the impact on lung function and quality of life together with the effects of medical and physiotherapy treatment on gastro-oesophageal function.