The ECL cells in the fundic mucosa from five different groups of fasted rats were examined by means of electron microscopy; in the control animals, the majority of the secretory granule of the ECL cells contained electron-dense material. Previous studies in our laboratory indicate that this material probably represents a catecholamine. In the second and third groups, in which truncal vagotomy plus pyloroplasty was performed, the secretory granules were depleted of their content. In the fourth group in which vagotomized animals were treated with iproniazid and L-dopa, the mature secretory granules were depleted but formation of new granules was apparent. In the fifth group, in which pyloroplasty alone had been performed, the content of the granules was the same as in the control group. It was concluded that the endocrine function of the ECL cells is under vagal control and that vagotomy causes release of catecholamines from these cells.