The transition of concentrations of FT-207 and 5-FU in the tumors as well as blood, along the process of time after administration of UFT, was studied from 32 cases of head and neck cancer patients. Comparing the initial administered group to the continual administered group on the blood concentration, and comparing also the irradiated group to the non-irradiated group on the tumoral concentration, the following conclusions are drawn.1. On the blood concentrations, FT-207 showed the highest at 2-hours' measure and gradual decline, however, 5-FU reached its peak within 1 hour and then fell rapidly.2. Concentrations of the continually administered group were higher than those of the initially administered group.3. On the tumoral concentrations, measurement at 6-hours was the highest not only FT-207, but 5-FU, and remains high for at least 10-hours.4. Concentrations of the irradiated group were higher than those of the non-irradiated group.5. On the comparison between the blood and the tumoral concentration, FT-207 of the former was almost half that of the latter upon measurement, i.e. at 6-hours, between the irradiated group and the continually administered group. On the other hand, the T/B value of 5-FU was almost 26 between the same groups.6. From the cases which both the concentrations of the blood and the tumors were simultaneously counted, these conclusions were confirmed. Moreover, the same tendencies were shown in the tumor of the neck lymphnode metastasis, and there were slight differences among the locations in one tumor.Thereafter, UFT provided good safety and left a high tumoral concentration, especially 5-FU, over a long period of time. As the continual administration of 400 mg/day of UFT, divided into two a day, associated with radiation therapy should be a most valuable therapy, the good clinical results may be expected.