Several gastric mucosal diseases and the response to powerful gastric secretory inhibitors are accompanied by hypergastrinaemia. When the gastric mucosa is functioning normally, hypergastrinaemia may be dangerous as a consequence of gastric hypersecretion. When the gastric mucosa is functionally abnormal, hypergastrinaemia produces no apparent adverse effects on health. However, the diseases giving rise to hypergastrinaemia are very dangerous because they are often the precursors of gastric cancer. In view of the probable mechanisms of gastric carcinogenesis, it is argued that therapeutic achlorhydria is also potentially dangerous irrespective of the absence or presence of 'hypergastrinaemia'.