The idea presented here is that, in gastric mucosa, two independent regulatory systems use the same transmitter: histamine molecules. The IgE/mast cell system is dispersed throughout the body, while the other regulates the gastric acid secretion. IgE molecules in gastric mucosa are attached to the mast cells. Mast cells release histamine molecules after the antigen has been recognized by IgE. These molecules normally act on vascular Hi receptors to promote extravasation and chemotaxy. Gastrin molecules are released from antral G cells to stimulate gastric acid secretion. Their influence on parietal cells is indirectly augmented by gastrin governed release of histamine molecules from enterochromaffin-like cells. These histamine molecules normally act on H2 receptors of parietal cells to promote gastric acid secretion. Chronic infection of gastric mucosa (i.e. with Helicobacter pylori), autoimmune disorders or repetitive mucosal exposure to the same antigen, can develop chronic inflammation of gastric mucosa. Gastric acid secretion is diminished with secondary hypergastrinemia and increased release of histamine from enterochromaffin-like cells in an attempt to stimulate the few remaining parietal cells. Hypothetically, increased concentrations of released histamine in gastric mucosa might activate the vascular H1 receptors with extravasation and aggravated inflammation. This can further decrease the number of active parietal cells, reduce gastric acid secretion and potentiate hypergastrinemia. In this hypothetical setting, H1 blockers might reduce the damage by abolishing the vascular reactions. The prolonged antigen load on gastric mucosa can promote production of specific IgE antibodies. Further exposures to the same antigen degranulate sensitized mucosal mast cells. Liberated histamine can produce extravasation through the vascular H1 receptor and, hypothetically, local hyperacidity through the parietal cell H2 receptors. The result would be hyperacidity and hypogastrinemia with possible ulcer disease. Some individuals are more predisposed to IgE production or have increased numbers of mast cells and that might explain why only some people develop ulcer disease after H. pylori infection.