Prolonged infusions of 5-fluorouracil (5-FU) have been used since the early 1960s, but recently there has been a major resurgence of interest, partly because of the advent of electronically controlled portable infusion pumps. This paper looks at the published data on continuously infused 5-FU in breast cancer. As a single agent, bolus 5-FU has a response rate of around 25%; this includes many patients in older series who were chemotherapy naive. The overall response rate across all the studies with continuously infused 5-FU is 29%. However, the majority of these patients were heavily pretreated, and response rates of up to 54% have been reported. What is more encouraging is the response rate in combination chemotherapy--even for pretreated patients with metastatic disease, response rates up to 89% have been found. However, this level of benefit brings a new toxicity--palmar--plantar erythrodysaesthesia; and of course myelotoxicity still remains a problem in the combination regimens. Randomised trials to assess the role of infusional 5-FU are now indicated.