Floxuridine (5-FUDR) was administered by continuous venous infusion using an ambulatory portable pump in a phase I study designed to establish the optimal (maximal) daily dose rate to deliver a minimum of 14 days of drug therapy. The major determinant of toxicity was dose rate rather than cumulative dose. Patients receiving greater than 0.15 mg/kg/day developed dose-limiting diarrhea at 7-14 days (median, 10), while patients receiving 0.1-0.125 mg/kg/day were treated for 18-78 days without adverse effects. The recommended daily dose rate for continuous-infusion schedules of 14 days is 0.15 mg/kg/day.