[en] As a result of the literature survey and from the authors' own data on assessing the variations in the median lethal dose and average life span of animals exposed at different dose rates, as well as fron the experimental material on the formation of the effective doses in the course of protracted and chronic exposures, the coefficient has been calculated characterizing the degree of the radiobiological effect variations for different animal species and dose rate ranges. Extrapolative values of the coefficient are obtained for man upon irradiation at different dose rates