The "Criteria for Evaluating the Efficacy of Chemotherapy/Radiation Therapy in the Treatment of Gastric Cancer" are now widely used in Japan. To assess the validity of the criteria, the relation between the antitumor effect evaluated by the criteria and the survival of patients with gastric cancer was analyzed. The subjects were 169 patients with unresectable advanced gastric cancer who were entered into a randomized comparative trial of tegafur plus mitomycin C, or UFT (a combination of uracil and tegafur in a 4:1 molar ratio) plus mitomycin C. Irrespective of their performance status, disease extent and chemotherapy regimen, responding patients showed improved survival over non-responding patients. If the primary gastric lesion responded to chemotherapy, prolongation of survival was noted in patients with a measurable gastric lesion as well as in those with a non-measurable but evaluable gastric lesion. No improvement in survival was recognized among patients having a primary gastric lesion which did not respond to chemotherapy, even if the metastases showed a response. The results obtained in the present study indicate the validity of the criteria, except for diffusely infiltrating gastric lesions.