[en] On the basis of the studies conducted in three independent laboratories (in France, USSR and USA), that have demonstrated, on various biological objects, the necessity of the natural radiation background (NRB) for the normal development of biota, the author postulates the universality of the phenomenon of hormesis that is observed under the effect of atomic radiation on biota. It is suggested that doses exceeding NRB should be considered low for a given species when the phenomenon of hormesis, for this species, is obsered. In determining the risk, the presence of hormesis in the radiobiological effects does not permit us to extrapolate the regularities obtained with high doses to those obtained with low doses