Abstract
During the course of the observation of peptic ulcer, we found the chronic myelogenous leukemia in four patients, and the blood histamine, serum gastrin and serum serotonin levels were determined. All four cases showed higher blood histamine level with increase of basophilic cells. Serum gastrin and serum serotonin levels were found to be within the normal range. Hyperhistaminemia with increase of basophilic cells found in all four cases had peptic ulcer formation with chronic myelogenous leukemia, which were throught to be one of the etiologic factors.