A case of the Zollinger-Ellison syndrome, presented with watery diarrhoea, malabsorption and multiple duodenal ulcers. Resection of a gastrinoma from the head of the pancreas was ineffective. Cimetidine, administered for more than 30 months produced an immediate and sustained relief of symptoms with a gain in weight of 19 kg and improvement of the biochemical features of malabsorption. Gastric acid secretion has been markedly inhibited and duodenal ulceration healed.