The etiology of adenomas in the stomach and duodenum in patients with familial adenomatous polyposis (FAP) is unknown. In this study the plasma concentration of epidermal growth factor (EGF), and other gastrointestinal polypeptides with a possible trophic effect on the gastrointestinal mucosa, was unchanged before and after meal stimulation. In 3 of 7 patients an increased EGF immunoreactivity was found in duodenal adenomas. This study has not indicated that regulatory peptides are involved in development of duodenal polyps in FAP. but suggests further studies to determine the role of EGF in FAP.