At increasing use of high-dose 5-fluorouracil-based chemotherapy for metastatic colorectal and gastric cancer complicated drug-induced colitis is observed more frequently. From May 1998 to November 2000 we observed 6 cases of 5-fluorouracil-induced colitis, in which we looked for involvement of small intestine. We report summing up on the 6 cases including both endoscopic and histological findings in both sites of the gut.In 2 men and 4 women (age 49-78 years) with advanced colon (n = 2), gastric (n = 3 ) and gallbladder (n = 1) cancer a palliative weekly high-dose infusional 5-fluorouracil (2,6 g/m(2)/24 h) and folinic acid (500 mg/m(2)/2 h) chemotherapy was performed. Few days after 1-5 chemotherapy courses the patients were admitted to our hospital with abdominal pain and partly severe watery diarrhea (up to 20 times evacuations/per day). The stool cultures were negative and there were no proof both of clostridium difficile and his toxin A and B. In 4 patients colonoscopy showed different grades of colitis up to diffuse erythema and microlesions, 2 patients had no visible lesions. In 4 patients endoscopy of the upper GI-tract showed a severe inflammation (n = 1) and a fibrinopurulent exsudate, severe edema and isolated ulcerations (n = 3) of jejunum after gastrectomy or duodenum with intact stomach. In the histological assessment different grades of 5-FU-induced colitis without (n = 2) or with (n = 4) involvement of the upper small intestine destruction of the superficial mucosa and crypts (epitheliumapoptosis) were found. 5 patients were treated by antibiotics (vancomycin n = 2, metronidazole n = 3), glucocorticoids (n = 5) and Saccaromyces cerevisiae (n = 3). After 8-10 days the patients were complete free of symptoms. One patient died due to the enterocolitis.The present cases demonstrate that high-dose 5-fluorouracil-based chemotherapy not only induces a colitis but also may involve the upper small intestine tract. Consequently, it represents an increasing and serious adverse event of high-dose chemotherapy. The etiology of the enterocolitis (drug- or bacterial-induced) needs further investigations in order to find a causal therapy and/or prophylaxis.