The H+, K(+)-ATPase inhibitor omeprazole has been made available on a compassionate basis for patients with Zollinger-Ellison syndrome considered resistant to, or with side-effects on, histamine H2-receptor antagonists. By December 1985, the first 80 patients, from 46 centres in 11 countries, had been treated for periods of 2 days to 4 years. Basal acid output was decreased to the desired level of less than 10 mmol.hour-1, and symptoms were rapidly relieved. Acid secretion and laboratory variables were checked regularly and endoscopic examinations made at intervals. Dosage was adjusted primarily on the basis of basal acid output, but also if symptoms recurred. The starting dose was generally 60 mg daily and the median dose ranged between 60 and 70 mg daily over the study period. There was no evidence of tachyphylaxis. More than 90% of the patients were successfully controlled on total daily doses of 120 mg or less; one-third of patients required divided doses. Tolerance was good: there were no obvious drug-related effects on laboratory variables, including fasting serum gastrin, and there were very few adverse events. Thirteen patients died (11 of the primary disease and two of other causes), four underwent successful tumour resection, six underwent total gastrectomy (though acid secretion was controlled in five), four patients' treatment was changed to other medical therapy, and one was lost to follow-up. Omeprazole thus appears to be both safe and very effective in controlling acid hypersecretion in this group of patients, and to provide a suitable alternative to total gastrectomy.