[en] Full text: In 1984, the discovery of the existence of radioadaptive response (RAR) revitalized the old concept of radiation hormesis. The RAR can be defined as a decreased radiosensitivity of living organisms after irradiation with a low dose. Today there is a controversy on the possible implications of RAR in the estimation of risks of low-level radiation exposures. Several recent reports indicated that RAR can induce beneficial phenomena that protect the cells against naturally occurring as well as radiation induced alterations that lead to cell transformations. Furthermore, it was indicated that RAR could induce processes that increase the latency for development of acute myeloid leukemia (AML), increase the rate of living fetuses and reduce the incidence of congenital malformations, or even increase the survival rate of animals after a high-level irradiation. Surprisingly, it has even been indicated that chronic low doses can increase the life span of animals. On the other hand, there are reports indicating that the induction of RAR in some cases, such as biological dosimetry and radiotherapy, can be a problematical phenomenon. Even though RAR is a real phenomenon, it should not be ignored that in some cases the adapting dose may induce a synergistic effect. We indicated that some of the individuals show extraordinary synergistic effect. On the other hand, there is a controversy in the induction of RAR in G₀ cells. Since the majority of human lymphocytes are in the G₀ phase, the induction of RAR in G₀ phase would be necessary for any possible implication of RAR in the estimation of the risks of low-level radiation. As a general rule the induction of RAR can be strongly dependent on the experimental systems or biological end points. This paper addresses problems concerning implications of RAR in the estimation of the risks of low doses of ionizing radiation and modification of radiation protection regulations. In spite of the fact that the existence of RAR can not be denied, at this stage it would be premature to use the results of RAR studies for radiological protection purposes. Our findings concerning problematical implications of RAR in radiation protection are in good agreement with the UNSCEAR-94 report