A gastrinoma was found in 12 of 23 patients with Zollinger-Ellison syndrome. Those with gastrinoma were not different from those without as regarded fasting gastrin level, increased gastrin secretion after secretin and calcium, acid secretion, or survival time. Five of the 23 patients have died, four immediately postoperatively, the fifth of the metastasizing tumour. Treatment with the H2-receptor antagonist cimetidine avoided emergency operation and thus decreased operative mortality, giving time for localization by ultrasound, computed tomography and selective arteriography. The rate of false-negative results was high. Transhepatic selective catheterization of the pancreatic veins with gastrin determination gives localization of the tumour and identification of the secreted hormone. In three patients tumour resection was possible under cover of H2-receptor antagonist administration which normalized gastrin and acid secretion. There is a change in the treatment of the Zollinger-Ellison syndrome, away from total gastrectomy to conservative treatment with H2-receptor antagonists and an attempt of curative treatment by removal of the tumour.