The enterochromaffin-like (ECL) cells represent the predominating endocrine cell population in the oxyntic mucosa of the stomach. They are under the influence of gastrin. Recently, a histamine production was shown within the secretory granules of ECL cells. ECL cells appear to play a crucial role in the physiology of gastric acid secretion. There are many unknowns concerning the intervention of other trophic factors in addition to gastrin and concerning the receptors located on the cells. ECL cell hyperplasia is a well documented consequence of hypergastrinemia. The latter can result from a gastrinoma or from a reduction of gastric acid secretion related to pernicious anemia or to long-term treatment with antisecretory drugs.