to assess the variability of the levels of chromosome aberrations induced by the in vitro irradiation of lymphocytes of breast cancer (BC) patients in comparison with healthy individuals. Materials and methods. Samples of peripheral blood for lymphocyte cultures were obtained from 44 healthy women and 37 primary patients with BC (T1-2N1M0). Lymphocyte X-ray irradiation was carried out at G0 and G2 phase of lymphocyte cell cycle (G0 and G2 assay) with the dose of 1,5 Gy before PHA stimulation in G0 assay and 0,5 Gy - at 47 h of cultivation in G2 assay. Preparations of metaphase chromosomes were made according standard protocols. Results and conclusions. Inter-individual variation of G2 chromosome aberration yields was significantly higher in comparison with G0 chromosomal radiosensitivity in both examined groups. According to G2 assay the fraction of individuals with elevated chromosomal radiosensitivity among healthy women and BC patients was 11.4 and 38 %, respectively. The results obtained support the concept of association between predisposition to BC, radiationinduced G2 chromosomal instability and efficiency of DNA repair activated by cell irradiation in G2 phase. It is assumed that individuals with elevated G2 aberration scores from the control group need further examinations on the BC risk and primary prevention of radiation induced cancer.