It is well known that ionizing radiation causes modification and destruction of nitrogenous bases in DNA molecule. There are also local breakages of hydrogen bonds (partial denaturation) both in the lesion sites mentioned above and in other sites of the macromolecule. To reveal the amount of some of these damages we applied circular dichroism and UV absorption spectroscopy. Radiation-induced changes in DNA structure influence its UV absorbtion spectrum in different ways: partial denaturation causes hyperchromic effect, while destruction of the bases results in hypochromic shift. At the same time both of them result in the same changes in DNA CD spectra: the decrease in intensity. We attempted to segregate the described damages in DNA structure and studied the influence of DNA ionic surroundings on the radiation effect. We have demonstrated that the radiation efficiency of base destruction and partial denaturation increases with decreasing concentration of NaCl in irradiated solution. The substitution of a portion of Na⁺ ions on Mg²⁺ with the total ionic strength remaining constant (0.005 M) does not influence the radiation efficiency. At the higher electrolyte concentration (3 M) the yield of bases destruction is smaller in MgCl₂ solutions than in NaCl ones, whereas the secondary structure of irradiated DNA is destabilized stronger in MgCl₂ solutions. Also we have investigated the DNA spectral parameters in the presence of some biologically active compounds in irradiated solutions such as aliphatic alcohols, catechin, epicatechin and caffeine. It has been shown that all of these compounds reveal a radioprotective properties.