Enterokinase, alkaline phosphatase and sucrase were measured in human duodenal mucosa before and after intravenous injection of glucagon. A net increase in mucosal enterokinase, but not in alkaline phosphatase or sucrase, was observed during the 15-min period following the injection of glucagon. On the intravenous administration of alanine, a known stimulator of the endogenous secretion of glucagon, a similar rise in mucosal enterokinase was observed.