To study the effects of sudden withdrawal of long-term maintenance therapy with omeprazole for up to 4 years, 14 patients with resistant reflux oesophagitis were asked to stop their treatment temporarily. Ten days after withdrawal median basal acid output had increased significantly (p = 0.01) from 0 (range, 0-1.18) on day 1 to 1.95 (range, 0-8.45) mmol/h on day 10. Median serum gastrin levels were raised during treatment with omeprazole but decreased significantly from 166 to 42 ng/l within the 10 days of the study (p = 0.01). The median integrated gastrin response after meal stimulation decreased significantly (p less than 0.001) from 758.6 ng/l on day 1 to 267.9 ng/l on day 10. On day 10 after withdrawal of omeprazole all patients had endoscopic and symptomatic evidence of recurrent oesophagitis. Reflux patients receiving maintenance treatment with omeprazole for up to 4 years showed prompt normalization of serum gastrin levels and return of gastric acid production within 10 days after stopping the treatment. Consequently, there was a fast recurrence of aggravation of reflux symptoms and oesophagitis.