A new statistical method to study repair mechanism of individual cells exposed to ionizing radiation is presented. The method is based on deviations from the Poisson distribution of observed chromosome aberrations and allows to determine the efficiency of repair mechanisms of individual cells. On basis of the dose-effect curves and the chi-square analysis, the ratio between the variance and the mean value of the observed aberration distribution could be calculated and related to the efficiency of the cellular repair mechanisms. The method has been tested on human lymphocytes and CHO-K1 cells exposed to different radiation species. In the case of high-linear energy transfer ion irradiation a correction due to Neyman A statistics has been introduced.