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The effects of bilateral adrenalectomy on the serotonin-, somatostatin-, and gastrin-immunoreactive cells in the rat gastrointestinal tract were studied four weeks after surgery. Body weight was reduced and the small intestine shorter in adrenalectomized animals compared with controls, while no changes were found in the histology of the mucosa. In the adrenalectomized animals the number of serotonin-immunoreactive cells was increased in the cecum and large intestine, while the somatostatin-immunoreactive cells were decreased in number in the antrum and increased in the corpus, cecum, and large intestine. The gastrin-immunoreactive cells in the antrum were not affected in number, but their nuclear size was enlarged, possibly indicating increased cellular activity.