The clinical, microscopic, immunohistochemical and ultrastructural features of 7 gastrinomas and 1 combined carcinoma-carcinoid tumor were evaluated. The tumors were located in the pancreas or duodenal wall in 6 cases, and on extragastro-enteropancreatic sites in 2 (liver or peripancreatic lymph node). All patients had the Zollinger-Ellison syndrome, 3 of them with additional bleeding and 1 with diarrhea. One patient with gastrinoma had additional tumors characteristic of the MEN-I syndrome. Immunohistochemistry showed gastrin and neuron-specific enolase-positivity in all of the tumors. Somatostatin was found in 4 cases, and single cell glucagon, pancreatic polypeptide. S-100 protein, keratin as well as carcino-embryonic antigen positivity in another few. Additional hormone production did not appear to be connected with biological behaviour of the tumors or with the clinical symptoms.