Combined oesophageal and gastric 24-hour pH monitoring and oesophageal manometry were performed in 19 patients with resistant reflux oesophagitis after short-term therapy with omeprazole (40 to 60 mg daily) or during maintenance treatment with omeprazole (20 to 80 mg daily). Omeprazole's effects on acidity were analysed as well as any possible influence on oesophageal motility. A pH in the stomach of below 4 was present during considerable periods of time (in 27 of 29 measurements), particularly during the night. As a consequence, pathological gastro-oesophageal reflux occurred, particularly in the supine period. Insufficiency of the lower oesophageal sphincter was present in all but one patient; decreased or virtually absent motility of the oesophagus was found in 63% of the patients. Combined intragastric and intra-oesophageal pH monitoring, with oesophageal manometry, may contribute to the management of patients with reflux disease resistant to treatment with omeprazole. The present study emphasizes the need to individualize therapy in patients with refractory gastrooesophageal reflux disease.