The different cellular responses to high (suppressive) and low (stimulant) doses of atomic radiation suggest understanding of radiation hormesis, since the well developed mechanisms of damaging effect of atomic radiation (radiodamage of DNA, chromosomal aberrations, death of radiosensitive cells) cannot explain the converse effects of low stimulant radiation doses. Here the direct or indirect excitation of membrane receptors comes to the foreground. The excitation activates membrane-bound enzymes which control many vitally important processes. Now that an increasing proportion of the general population is exposed to low chronic doses of ionizing radiation, the knowledge of radiation hormesis acquires great importance, particularly, for temporal predictions of its consequences. Although this problem is far from complete understanding, it is, undoubtedly, wrong to estimate the hazard of the low radiation doses by straight extrapolation of the data obtained with much higher doses and during shorter time periods.