Severe reflux oesophagitis, which is resistant to treatment with high doses of H2-receptor antagonists, can be treated successfully with the H+,K+-ATPase inhibitor omeprazole. Experience from more than 3 years of continuous treatment with omeprazole, in doses adjusted to prevent recurrences, has demonstrated its high efficacy in the long-term management of the patients. The use of this drug emphasizes the importance of long-standing, effective, 24-hour acid inhibition for reflux oesophagitis. Fasting gastrin levels increase 2-fold during the initial treatment period but continued treatment does not induce any further elevation. Omeprazole does not induce pathological changes in the endocrine cell population of the gastric oxyntic mucosa, though in some patients an increase in the argyrophilic cell volume density during omeprazole treatment has been reported. Careful surveillance of the safety profile of this drug is continuing.