The histamine H2-receptor antagonist metiamide is an inhibitor of endogenous and stimulated gastric-acid secretion. It appears to have therapeutic possibilities in duodenal-ulcer disease. Three patients exhibiting the Zollinger-Ellison syndrome have been treated with this drug for six months or more. Rapid symptomatic improvement occurred in each case, followed by ulcer healing. There were also reductions in gastric secretion and consistent changes in the fasting serum-gastrin concentration. On patient relapsed temporarily during therapy. There have been no side effects. It is concluded that, in the short term, metiamide is of benefit in the Zollinger-Ellison syndrome.