Continuous venous infusion of 5-fluorouracil (5FU) was investigated in 18 patients with measurable advanced cancer of the pancreas. 5FU was given for 7 days in a dose of 500 mg/m2 by continuous venous infusion over a 24-hour period and then followed by a dose of 170 mg/m2 for more than 28 days. Ten patients had no change including 1 patient with minor response, and 4 patients had disease progression. Serum CA19-9 levels were measured serially after chemotherapy in 13 of 14 evaluable patients. In 3 of 10 patients who showed high levels before treatment, serum CA19-9 levels were significantly decreasing after treatment.