A factorial longitudinal study will be undertaken in adults with cystic fibrosis. Results will be compared with age matched healthy controls. It is not deemed appropriate to randomise patients with gastro-oesophageal reflux(GOR) to a treatment versus no treatment group as immediate treatment for GOR once diagnosed is regarded as obligatory. Subjects: 180 adults with CF will be recruited from the Adult Cystic Fibrosis Unit at the Alfred Hospital to participate in the study. The ambulatory studies will be undertaken during baseline state in the outpatient setting. Fifteen age matched control subjects will be recruited from the general population.

Subjects who give their consent for participation in the study will undertake the following outcome measures:

1. Demographic data including age, gender, BMI, prescribed medication at the time of the study, lung function tests including FEV1, FVC, FEV1/FVC ratio and MMEF, genotype, pH of saliva and sputum.
2. Structured symptom questionnaire using a reliable valid measure developed by Carlsson et al 1998 will be used to assess patient's symptom scores.

3. Dual-channel 24hour oesophageal pH monitoring will be undertaken using a digitrapper (Medtronic, Sweden)and dual antimony tipped probe (Synectics, Sweden). Following calibration of the probes the distal antimony tip is positioned 5cm above the upper border of the lower oesophageal sphincter and the proximal probe 15 cm above the distal probe in the upper oesophagus.The patient will be instructed in using the three event buttons on the digitrapper recording start and finish time of meals, upright versus supine positioning and reflux episodes. The subject will be provided with a detailed 24hr 'Activity Diary' to record all meals (including percutaneous gastrostomy feeds), positions and activities including usual chest physiotherapy and physical exercise.The recorded pH information is downloaded into a computer program for analysis. The following indices will be measured in the distal and proximal oesophagus:

   • Number of reflux episodes
   • Fraction of reflux time
   • Number of reflux episodes with duration longer than 5 minutes
   • Duration of longest episodes in minutes
   • DeMeester score (an overall weighted score of gastro-oesophageal function).
4. Quality of life questionnaires: SF36, Quittner CF Questionnaire (CFQ), Dietary and Bowel Symptom Questionnaires.
5. Chest radiographs