The paper summarizes the results of studies of 85 individuals exposed in the Southern Ural region. The spontaneous frequency of the cells with micronuclei (MN) in a population of human blood lymphocytes after PHA stimulation and cytokinetic block with cytochalasin B has been determined. The sensitivity of lymphocytes to the irradiation at the dose of 1.0 Gy and the adaptive response (AR) after the irradiation at the low adaptive dose of 0.05 Gy, and the challenge dose of 1.0 Gy 5 h later have been studied too. It was shown that the peculiarity of the Urals population consists in a higher individual variability of the frequency of cells with MN in all groups have been investigated (spontaneous, after acute irradiation in the dose 1.0 Gy) in comparison with Moscow people. The proportion of persons with a significant AR in the Urals groups was considerably lower than that identified among Moscow residents, and the number of persons with enhanced radiosensitivity increased following low-dose irradiation. We can suppose that prolonged action of low level radiation with another ecological factors, living in the contaminated regions result in the enhancement of the sensitivity to the genotoxic agents in the separate individuals.