A randomized controlled trial involving 13 institutions in Japan was conducted in order to compare the efficacy of tegafur plus mitomycin C (MMC) (Regimen A) and UFT (a combination of uracil and tegafur at a molar ratio of 4 to 1) plus MMC (Regimen B) for patients with advanced gastric cancer, who had not received any prior cancer chemotherapy. Regimen A (tegafur + MMC) consisted of 5 mg of MMC/m2/week given intravenously, and 500 mg of tegafur/m2/day given orally. Regimen B consisted of the same schedule of MMC and 375 mg of UFT/m2/day given orally. One hundred and eighty-six patients with primary gastric cancer were entered; 183 were eligible and 3 were ineligible for the study. A total of 169 were evaluable for efficacy of the treatment, including 90 patients with Regimen A and 79 with Regimen B. A response rate of 7.8% (7/90 cases) for Regimen A and one of 25.3% (20/79 cases) for Regimen B were obtained, indicating a significantly higher response rate for Regimen B according to the Criteria for Evaluating Efficacy of Chemotherapy/Radiation Therapy in the Treatment of Gastric Cancer (P = 0.004). Regarding side effects, no marked differences in either severity or incidence were observed between the two groups. The group assigned to Regimen B showed a significant survival advantage after adjustment for major prognostic factors using a proportional hazards model (P = 0.0398). Moreover, a close correlation of antitumor effect and survival duration was found when the above criteria were used.