The study of the cellular response and its mechanisms to the chronic influence of ionizing radiation requires the using of the up-to-date universal methods both for different tissues with various proliferative activity and different animal species. We propose a number of cytological and molecular methods (DNA damage assay, apoptotic cells rate determination, micronuclei assay) that not excludes a possibility to use an additional histological methods at the same time. The optimal approach has been established for cell suspension preparation from different tissues to study the level of genome damage etc. The main steps of cell suspension preparation for the red bone marrow, spleen, thyroid gland have been described. We carried out experiments on the level of genome damage determination in laboratory mouse lymphocytes, spleen, red bone marrow and thyroid cells as well as in Drosophila Melanogaster brain ganglion.