A randomized controlled trial has begun in Japan to compare orally administered S-1 with intravenous gemcitabine (GEM) as adjuvant chemotherapy for patients with curatively resected pancreatic cancer. Patients are enrolled within 10 weeks after pancreatectomy to be treated for six months after assignment to either S-1 (80 mg/m(2)/day for four weeks, repeated similarly every six weeks for a total of four courses) or GEM (1000 mg/m(2) on days 1, 8 and 15, repeated similarly every four weeks for a total of six courses). The primary endpoint is overall survival; secondary endpoints include relapse-free survival, incidence of adverse events and health-related quality of life. Each treatment arm includes 180 patients, providing an expected hazard ratio of 0.87 and an upper margin of 1.25 (two-sided alpha-error, 0.05; power, 0.8). Follow-up abdominal computed tomography is repeated every three months during the first two years, then every six months for three years.