One hundred and twenty-four patients with a diagnosis of metastatic gastrointestinal cancer and no prior therapy were included in this clinical study of carmofur monotherapy, 300-500 mg/m2 daily for 6 weeks. For the 115 evaluable patients, the response rates were 19.4% in gastric cancer, 27.2% in cancer of mobile colon, and 12.5% in rectal cancer. No objective responses were seen in 38 patients with pancreatic cancer, although the disease of 13 of these patients has remained stable over a considerably long period of follow-up. The toxicity profile was interesting; the main adverse effects were urinary bladder symptoms and flush. Hematologic toxicity was minimal. The treatment proved to be safe and could be used for outpatients.