Ten patients with metastatic breast cancer refractory to multiple chemotherapeutic regimens as well as hormonal therapy were treated with continuous intravenous infusion of 5-fluorouracil (5-FU) at 200-300 mg/m2/24 h through a Broviac catheter using a Cormed pump. The treatment was continued until toxicity developed and restarted after resolution of the toxicity. Most common dose-limiting toxicities were mucositis and diarrhea. No grade II or worse myelosuppression was documented. All the patients had received 5-FU by bolus injection before entering the study. We observed three partial responses and one improvement, with two patients continued on the study (396+ and 90+ days, respectively). We conclude that continuous infusion of 5-FU is safe and tolerable even by heavily pretreated patients with poor performance status and is not cross-resistant to bolus injection of 5-FU and other chemotherapeutic agents. Our report warrants further investigation.