In a new model, chronic duodenal ulcers are generated by irradiating the lower mediastinum of mice with single doses of X-rays. Histamine, a potent secretagogue, may have a role in the aetiology. Seven days after irradiation, the lag period for ulcerogenesis, mice were given a gastric perfusion test. In mice given irradiation to the lower mediastinum tissue histamine in the oxyntic region of the stomach assayed after perfusion was significantly lower than that of controls. Acid and peptic activity were not different from controls. Histamine release may mediate the abscopal ulcer without increasing acid and peptic activity.