[en] In order to observe the radiobiological characteristics of cervical cancer, the author carried out irradiation of ⁶⁰Co in 16 cases of cervical cancer. The primary lesion of each case was exposed to radiation of 100 R once a day, 40 times in sequence, totaling 4,000 R. To evaluate this results, the vaginal smears were obtained everyday and examined for changes in cancerous cells caused by the irradiation. The results of our study showed that cervical cancer could be classified into three groups according to the radiosensitivity of its cancerous cells. In the group of low-radiosensitivity (11 cases of 16), the cancerous cells decreased gradually, and enlargement of the nuclei of the cancerous cells was observed from 2,000 R of irradiation, but the majority of the cancerous cells were those of nucleus after the irradiation of 4,000 R. In all of the 5 uterus removed, residual cancer lesion was noted. The radiocuability was unfavourable. In the group of high-radiosensitivity (4 cases of 16), the cancerous cells decreased remarkablly. Enlargement of nucleus was noted from 1,000 R of the irradiation, the cancerous cells of small-sized nucleus appeared with the irradiation of 3,000 R but the cancerous cells almost disappeared with the irradiation of 4,000 R. The radiocuability was favourable. In the group of combination of high-radiosensitivity and low-radiosensitivity portions (one case of 16), the cancerous cells decreased remarkablly until the exposure to the radiation of 2,000 R but thereafter did slowly. In a removed uterus, the cancer lesion was noted, but the prognosis was favourable. The foregoing results suggest that changes in the nuclear diameter of the cancerous cells in vaginal smears during irradiation can tell the radiosensitivity of the cancerous cells. (Kanao, N.)