Experimental model. Fractions characterized by different conditions of DNA structure, antioxidant status or different radiation and repair schedules. Intact cells represent complete cells with unchanged chromatin structure or intracellular radical scavengers (Fraction I/IV). Pre-treatment lysis of fraction (II) and (III) depleted histones and radical scavengers. Therefore, fraction (II) and (III) contained DNA stripped of histones +/− antioxidant DMSO. All samples were irradiated with 4 Gy. Fraction (IV) was twice irradiated with 4 Gy after 45 min of repair time. The experimental model was examined using 200 leukocytes/sample of each donor (n = 5).