A tissue specimen taken from the pancreatic tumor of a patient suffering from Zollinger-Ellison syndrome associated with a concurrent Cushing's syndrome was investigated both morphologically and immunohistochemically. Histologically, the tumor cells were found to be arranged in a cord or ribbon pattern. An immunohistochemical study revealed that the tumor nodule contained both gastrin and ACTH. Further, double stainings of the same section disclosed that the same tumor nodule possessed both hormones simultaneously, thus confirming the concurrent presence of Zollinger-Ellison syndrome and Cushing's syndrome. An electron micrograph of the tumor cell showed the presence of numerous endocrine-type granules in the cytoplasm. These findings substantiate the concurrent presence of the two characteristic clinical syndromes.