A rare case of the Zollinger-Ellison syndrome associated with hyperparathyroidism and ectopic gastric tissue in the lower esophageal mucosa is reported. Preoperatively the patient, a 53-year-old woman, had hyperchlorhydria and her fasting serum gastrin concentration was mildly elevated. There was a considerable increase in the gastric acid output and concentration of serum calcium after secretin infusion. At operation the patient had a gastric ulcer 10 cm in diameter, an islet cell tumour of the pancreas 14 cm in diameter, and ectopic gastric mucosa in the distal third of the esophagus. A gastrectomy was perfomed, the pancreatic tumour excised and part of the distal esophagus removed through a left thoracotomy. Four months after the operation the gastrin concentration had returned to low normal, but the serum calcium values remained high. One month later two parathyroid adenomas were removed which effectively cured the hypercalcemia.