Gut endocrine cells in a total of 122 intestinal-tract adenocarcinomas induced in inbred Wistar rats by 1,2-dimethylhydrazine dihydrochloride were examined histologically, ultrastructurally, and immunohistochemically for gastrin, somatostatin, vasoactive-intestinal polypeptide (VIP), and glicentin (enteroglucagon). Of the 122 tumors, argyrophil cells were detected in 42 tumors (34.3%) comprising 15 tumors of the well differentiated type and 27 tumors of the poorly differentiated type, including signet-ring-cell carcinomas. Of the 27 tumors of the poorly differentiated type, 12 were regarded as endocrine-cell carcinomas composed of numerous argyrophil or argentaffin cells and mucus-containing cells. Immunohistochemically, 7 of the 12 tumors had glicentin and two of these seven tumors also had gastrin and argentaffin cells synchronously. None of the tumors showed immunoreactivity for somatostatin and VIP. Nine of the 12 tumors metastasized to the lung, pancreas, liver, mesenterium, omentum, and lymph nodes. The metastatic foci of these tumors were also shown to have glicentin and argentaffin cells. Ultrastructurally, four types of endocrine granule were found in the tumor cells and amphicrine cells containing endocrine granules and mucous granules were noted. These endocrine-cell tumors were assumed to develop from totipotent immature cells of endodermal origin.