Eleven adult patients with nocturnal asthma, and gastro-oesophageal reflux documented by endoscopy or ambulatory oesophageal pH monitoring completed a double-blind cross-over study (4 week treatment, one week run-in and cross-over periods) comparing the effects of omeprazole 20 mg daily and placebo on asthma control assessed by symptoms, peak expiratory flow rate and bronchodilator usage. Omeprazole treatment did not improve asthma symptoms during the day or night, or peak expiratory flow rate readings. There was no difference in bronchodilator inhaler usage during omeprazole therapy. Treatment of gastro-oesophageal reflux with omeprazole in patients with nocturnal asthma and gastro-oesophageal reflux does not improve asthma symptoms or peak expiratory flow rate. This suggests that gastro-oesophageal reflux does not exacerbate bronchoconstriction in nocturnal asthma.