Continuous regional delivery of chemotherapeutic agents offers the prospect of maximising dose intensity at the site of localised disease, while minimising systemic toxicity. This prospective phase II study evaluates the efficacy and toxicity of hepatic arterial infusion of 5-Fluorouracil (5-FU) via an implantable Infusaid pump in previously untreated patients with localised but unresectable hepatic metastases from colorectal cancer. In 25 patients the response rate was 56% and median survival was 15 months, comparable to previous reports utilising fluorodeoxyuridine (FUDR). Twenty per cent of patients (all responders) survived longer than three years. Systemic toxicity was trivial, and the practice of reducing the intensity of therapy when nausea or a rise in alkaline phosphatase occurred avoided the previously described local toxicity of biliary sclerosis seen frequently with FUDR. In selected patients, particularly those with more limited disease, this form of therapy is effective and well tolerated and warrants further evaluation as an alternative to FUDR.