Summary Background: The antioxidant activity of estrogen has a be ne - ficial impact in Alzheimer’s disease. A variety of clinical stu - dies have demonstrated that estrogen replacement therapy in postmenopausal women results in a lower frequency of AD, delaying the onset of the neurodegenerative cascade. On the other hand, it has been demonstrated that estrogens may exhibit genotoxic effects, especially at elevated tissue concentrations. Therefore, the aim of this study was to determine whether b-estradiol induces DNA damage in the peripheral blood lymphocytes of healthy young females and males, healthy elderly females and males and females and males with Alzheimer’s disease. Methods: All experiments were performed using the alkaline version of the Comet assay (single cell gel electrophoresis), on six donors per each experimental group and controls. Results: In the Comet assay, a significant increase of DNA migration was observed in the lymphocytes of all treated groups (young and elderly females, young and elderly males, AD females and AD males) at all b-estradiol concentrations (50 mmol/L, 100 mmol/L and 250 mmol/L) used in this investigation. In all the experiments cell viability was over 80%. Conclusions: Lymphocytes are sensitive to the test concentrations of b-estradiol in the Comet assay regardless of gender, age and health condition of the examined subjects. Therefore, the role of b-estradiol in cellular DNA damage has been confirmed.