The combined effects of X-ray and UFT, which is a mixture of tegafur (FT) and uracil, were studied using C3H mouse mammary carcinoma. Tumors were irradiated with a single dose of 1,000 R, 2,000 R one week after intramuscular transplantation. UFT (FT 15mg/kg+Uracil 33.6mg/kg) was intragastrically administered 2 hours before irradiation. In the group treated by combination of UFT and 1,000 R, the dose modifying factor (DMF) of UFT was 1.28 on the tumor growth delay and 1.64 on the survival time. A decrease in pulmonary metastases was found in the group treated by combination of UFT and radiation. It is suggested that UFT is a useful oral drug for combined treatment with radiation.