We administered the anticancer drug 5-fluorouracil locally to treat rectal adenomas in four patients with familial adenomatous polyposis who had undergone total colectomy and ileorectal anastomosis. The drug was administered either in suppository form or in high concentration as a rectal enema. One patient was treated successfully with 5-fluorouracil suppositories without any side effects, but the suppository regimen had to be stopped in three other patients because of severe rectal urgency. However, one of these patients was treated effectively with rectal administration of a high-dose 5-fluorouracil solution. Adenomas near the anastomotic site or dentate line were difficult to treat. Although severe urgency was seen in most patients, we think that the intraluminal administration of anticancer agents may prove effective in treating polyposis of the rectum retained after colectomy in familial polyposis. It deserves further study.