To the Editor .—Patients with familial adenomatous polyposis (FAP) are at high risk for developing duodenal polyps. In the discussion of the article by Beckwith et al, 1 van Heerden was "... unaware of any biliary factors or any studies..." that sought to identify a factor that caused these polyps to develop. We have conducted several such studies, and have found the following: The distribution of upper gastrointestinal adenomas is maximal in areas exposed to bile, with marked periampullary clustering of tumors. Significantly more duodenogastric reflux of bile occurs in patients with FAP with adenomatous polyps in the stomach than in those patients without such polyps. The profile of bile acids in bile is abnormal in patients with FAP. The amount of DNA adducts (adducts are markers of exposure to carcinogens) is significantly greater in the duodenum of patients with FAP than in the non-FAP duodenum. Adduct labeling is greater