The lethal, mutagenic effects and the nature of mutations induced by decay of radionuclei incorporated into yeast cell were studied by K-cupture. The efficiency of inactivation per decay in a cell has been shown to be (2.23 +/- 0,70) X 10(-3) and (0.90 +/- 0.47) X 10(-3) for 54Mn and 85Sr, respectively. The efficiency of mutation production in ADE1 and ADE2 genes per decay is (1.25 +/- 0.57) X 10(-8) and (1.8 +/- 0.3) X 10(-9) for 54Mn and 85Sr, respectively, the lethal and mutagenic efficiency of 7Be being about zero. The relative mutagenic efficiency (RME), demonstrated as a ratio of the mutagenic efficiency of a mutagen to that or gamma-rays at the equal value of survival makes 0.25 for 54Mn and 0.1 for 85Sr. A frequency of the induced frameshift mutations was increased, in comparison with the frequency of mutations induced by clear beta-decay of radionuclei.