Purpose: A pilot study was performed to evaluate the tolerance and efficacy of a hepatic arterial infusion (HAI) of 5-fluorouracil (5-FU) and folinic acid (FA) in patients with unresectable liver metastases from colorectal carcinoma, Patients and Methods: In 11 patients, 135 applications of high-dose HAI of 5-FU/FA were administered, All patients had been intra-arterially pretreated, and 2 of them had received an additional intravenous therapy. The chemotherapy regimen consisted of a weekly HAI of FA 500 mg/m(2) over 1 h, immediately followed by HAI of 5-FU over 24 h, Four patients received a 5-FU starting dose of 2,000 mg/m(2) and 7 patients of 2,400 mg/m(2). One course consisted of 12 weekly applications interrupted by 1 week after 6 applications and 4 weeks after 12 applications. Results: The applied regimen caused only mild side effects, Nausea and vomiting were the most frequently side effects with 36 episodes out of 135 applications (WHO grade greater than or equal to 3: 2 episodes), Diarrhea was a minor problem occurring with 8 episodes (WHO grade greater than or equal to 3: 1 episode), There was no evidence of myelosuppression, hand-foot syndrome, neurotoxicity, and biliary sclerosis, A partial remission was observed in 3 patients, and a disease stabilization in 2 patients while the disease progressed in 6 patients under high-dose HAI of 5-FU/FA. Conclusion: The present pilot study demonstrates that the weekly high-dose HAI of 5-FU/FA is well tolerated and associated with very mild toxicity, Because of the encouraging response rate in patients, whose disease progressed under the conventional intra-arterial therapy either with 5-FU/FA or 5-fluorodeoxyuridine, this regimen seems to be an effective second-line treatment and should be evaluated in nonpretreated patients in a phase II study.