Forty-two cases treated by direct intravenous injection of FU are compared with 39 cases treated by three types of prolonged intravenous infusions. Less toxicity was produced in those cases in which the prolonged infusion technique was used. The therapeutic response in these cases treated by any of three types of prolonged infusion was as good as it was in these cases treated by any of three types of prolonged infusion was as good as it was in those treated by direct injection There was no loss of therapeutic effect, and no increased toxicity in those patients treated with one-half to one-hour infusion of FU in 250 ml of saline, as compared with those patients treated by longer infusions of FU in dextrose.