In 2014 the group of authors has reported that the elevation of the dose rate during tumor radiotherapy to several dozens of grey per second results in the decrease of normal tissue damage without change in tumor suppression, and has named it the FLASH effect. However, such peculiar effect has been described by a researcher in our laboratory, Dr. SV Kozin with VA Zolotov and NA Ponomareva (Institute of theoretical and experimental physics): ‘Hypoxic proton radiotherapy of solid Ehrlich tumors with different dose magnitudes’[Med Radiology. 1984, PMID 6087078]. They studied the damage of the ELD transplanted tumors and the skin of mice after proton irradiation with the dose rates from ‘usual’ to 6×107 Gy/s, and concluded: ‘The skin protection can be achieved by use of ultra-high dose rate and in this case it is associated with radiochemical depletion of oxygen’, and without diminution of tumor damage. The depletion of oxygen is still considered as one of the explanations of this effect. Consideration of the expediency and possibility of using an irradiation with a dose rate of tens of Gy/s in radiation therapy of tumors is now given a special attention. It has been already shown that less damage to the skin and other tissues occurs in comparison with damage after treatment at the ordinary dose-rate. Concerning the role of oxygen depletion in the FLASH-effect, it should be mentioned that, from the first sight, it could offer much larger protection of the tumors due to the already hypoxic state of some malignant cells. However, in our laboratory it has been shown that the treatment of animal tumors while mice normal tissues without or with less protection of breathed gas mixture containing only 10 or even 6 % O2 has resulted in substantial radioprotection of tumors. These effects deserve further studies.