A clinical trial was conducted in order to evaluate the anti-tumor effect and toxicity of a continuous infusion of 5-fluorouracil (5-FU) for metastatic colorectal cancer. Two-hundred and fifty mg/m2/day 5-FU was administered as a continuous infusion through an indwelling central venous catheter with ambulatory pump. Twenty patients with metastatic colorectal cancer which could be measured or evaluated were enrolled in the trial. The objective response rate was 35% (95% confidence interval, 14-56%). The response rates by site were 33% in liver, 17% in lung, 60% in lymph nodes, 50% in adrenal gland and 50% in primary lesion. The major toxicity was stomatitis (50%; grades 2 and 3 on Eastern Cooperative Oncology Group (ECOG) criteria) and hand-foot syndrome (40%; grades 2 and 3 on ECOG criteria). The sequence of toxicity was stomatitis first, followed by hand-foot syndrome. The median cumulative dose of 5-FU from the initiation of therapy to the onset of toxicity was 7125 mg in stomatitis and 17,875 mg in hand-foot syndrome. These toxicities were mild and reversible after a short interruption to the 5-FU infusion. Neither hematological toxicity nor serious catheter-related complications were observed. We concluded that continuous infusion of 5-FU was a feasible treatment for the patient with metastatic colorectal cancer, and manageable on an out-patient basis.