The use of secretin in the biochemical and roentgenologic diagnoses of a duodenal gastrinoma has been described. Preoperatively, the secretin test indicated that a gastrinoma and not a retained antrum was the cause of hypergastrinemia in a patient who had previously undergone Billroth II gastrectomy. Intravenous infusion of secretin during selective angiography resulted in greatly enhanced visualization of the tumor which allowed it to be localized to the duodenal stump. Several months postoperatively, the secretin test result had become negative, which presumably suggested that the tumor had been excised completely. Our experience has revealed that intravenous secretin might improve the diagnostic usefulness of selective angiography.