Gastroduodenal inflammation and ulceration have been frequently observed in patients receiving continuous hepatic arterial infusions of 5-fluoro-2'-deoxyuridine (FUDR) for liver malignancy. Thirty-five patients with metastatic colon cancer received hepatic arterial FUDR administered with implanted infusion pumps. At surgery, particular care was taken to identify and divide those vessels arising from the hepatic arteries distal to the point of cannulation that supplied the superior border of the distal stomach and proximal duodenum. None of the patients developed signs or symptoms of gastritis or ulcer attributable to chemotherapy. We contend that gastritis and ulcer in patients receiving hepatic arterial FUDR are due to misperfusion of drug into the upper gastrointestinal tract and that these complications can be largely avoided by use of appropriate surgical techniques.