The response of different physiological systems to ionizing radiation as modified by UHF irradiation of nonthermal intensity was investigated. The experimental rats were exposed to electromagnetic irradiation of the power flux density (PFD) 200 microW/cm2 30 min daily for 8 days and the next day they were exposed to single total-body gamma-irradiation at a dose of 5.5 Gy. Pre-exposure to UHF irradiation reduced 1.5 times the mortality rate of the test animals as compared to the controls. Immunobiological examinations revealed a significant increase of the stimulation index in the mitogen (PHA) induced lymphocyte blast-transformation reaction and a decrease of the autopatch count. The motor activity of the rats exposed for 20 min to gamma-irradiation at a dose of 0.34 Gy and the next day to UHF irradiation (PFD = 40 microW/cm2) for 1 and 5 min remained essentially unchanged. The imprinting of the chicks irradiated in early embryogenesis for 5 min with UHF (PFD = 40 microW/cm2) and then with gamma-rays at a dose of 0.36 Gy was disrupted.