This controlled trial compared to survival of 90 patients with locally advanced gastric carcinoma treated with either chemotherapy alone (5-FU and methyl-CCNU) or external radiotherapy of 5000 rad combined with the same chemotherapy. The minimum period of followup is 4 years. During the initial 12 months, combined modality therapy was associated with an increased number of early deaths attributable to progression of tumor within the radiation field, or nutritional and hematologic complications. During the second to fourth years of followup, patients treated with combined radiation therapy have shown a significantly lower death rate compared to those treated with chemotherapy alone, with eight of 45 patients alive and disease-free. Patients who received only chemotherapy, in contrast, have demonstrated a continued probability for tumor relapse and death, with three of 45 patients alive at 4 years. Palliative resection of the primary tumor was associated with an improved survival, independent of the form of postoperative therapy employed. It is possible that the superior late survival achieved with combined modality therapy in this program can be further improved with measures to decrease the toxicity of upper abdominal irradiation, and with the use of more effective forms of chemotherapy.