Curative resection of gastrinomas in patients with Zellinger-Ellison syndrome has been difficult because localization of gastrinomas, which are often multiple and metastatic, are difficult. Development of the Selective Arterial Secretin Injection test and the Intraoperative Secretin Injection test broke through the problem. We will present the cases of two patients - one with MEN-I and the other with sporadic duodenal gastrinoma - in whom gastrinomas were curatively resected assisted by these tests.