Histological and histochemical changes of the cervix by irradiation were investigated on 16 cases of carcinoma of the cervix. Maximum surface dose, 2,000-6,000R., was applied to the cervix with a special colpostat followed by radical hysterectomy 1-10 days later. The difference between irradiated areas and non irradiated areas was studied with following results. 1) The activity of non specific esterase increased in irradiated areas with expectation of a useful indicator of radiosensitivity. 2) SDH, LDH and G-6-P DH showed no change in their activity after irradiation. 3) The appeareance of mast cells has some relation with histological radiation effect. Increase of mast cells in number was noticed in good histological response.