Our of 140 patients treated with intravenous 5-fluorouracil, four developed ischaemic chest pain within 18 hours of either the second or third dose. In three of these patients the pain recurred after subsequent doses. Predose electrocardiograms in two cases were normal. None of the four patients had a history of ischaemic heart disease, although all had received left ventricular irradiation. Although cardiotoxicity is a rare complication of fluorouracil treatment, it merits wider recognition.