Among available drugs, omeprazole is the one that cures gastric acid secretion-related pathologies, including reflux oesophagitis which responds poorly to H2-receptor antagonists, most rapidly and efficaciously. This marked therapeutic action is thought to reflect the drug's capacity to adequately control parietal hydrochloric acid secretion. Our data suggest an omeprazole effect on human neutrophil function too. Neutrophils are more or less a constant, and often conspicuous anatomo-pathological component of the phlogistic processes associated with gastric acid secretion. A direct or indirect effect exerted by omeprazole on leukocyte function would be of great scientific-biological and therapeutic interest. Furthermore, it would contribute to marking the drug superior in terms of more rapid relief of the symptoms and range of therapeutic action.