[en] Comparative studies were made of immediate (within the first minutes) changes in intracellular ATP concentration after irradiation by different regimens. ATP concentration in cells at a stationary phase of growth increased after irradiation with a dose of 5 Gy, reaching its maximum within 30-40 min. Irradiation with the same total dose, by a dose of 5 Gy, reaching its maximum within 30-40 min. Irrardiation with the same total dose, by the regimen of 0.1+4.9 Gy at a 3-minute interval between the doses, did not cause alteration in the ATP content in cells. It was concluded that the absence of the increase in the parameter under study (ATP) after irradiation by the latter regimen indicated that preirradiation at a dose of 0.1 Gy inhibited the adequate developement of an early response to irradiation with a dose of 4,9 Gy