The studies concerned the response to bleomycin treatment in peripheral blood lymphocytes (PBL) of breast cancer (BC) subjects. The level of BLM-induced DNA strand breaks was evaluated using alkaline comet assay followed by visual scoring. The sensitivity to genotoxic exposure as well as the time-course of damage removal were estimated and analysed in comparison to control (healthy) subjects. Despite high inter-individual variability, the differences between the BC and non-cancer groups still proved to be statistically significant. Lymphocytes of the BC subjects appeared to be more sensitive to BLM exposure as shown by higher level of DNA damage. The DNA repair capacity was weaker in PBL obtained from BC patients than that in lymphocytes of controls.