[en] The influence is studied of 1-β-D-arabinofuranosylcytosine and hydroxyurea (Ara-C and HU, respectively) - inhibitors of repair and replicative DNA synthesis - on the formation and repair kinetics of DNA double-strand breaks (DSB) in peripheral human blood lymphocytes under radiations of different linear energy transfer (LET): gamma quanta and accelerated heavy ions. It is shown that lithium and boron ions with a LET of 20 and 40 keV/μm, respectively, have greater biological effectiveness against the DNA DSB induction criterion. The relative biological effectiveness of accelerated boron and lithium ions is 1.5±0.1 and 1.6±0.1, respectively. Under gamma-irradiation in the absence of inhibitors, efficient DNA DSB repair is observed during incubation. After five-hour cell incubation in the presence of inhibitors, some increase rather than decrease in the DNA DSB yield is observed. Under accelerated boron ions in normal conditions, as well as under gamma-irradiation, efficient repair of induced DNA lesions takes place. During cell incubation after gamma-irradiation, the effect of radiomodifiers results in a decrease in the amount of induced DNA DSB. The obtained results may indicate that under the effect of ionizing radiations of different LET on mammalian cells in the presence of DNA synthesis inhibitors Arra-C and HU, DNA DSB repair takes place. It is concluded that under gamma-irradiation of cells, no DNA DSB repair is observed due to a large contribution of DNA single-strand incision breaks, which are formed in the post-irradiation period during the excision repair of nucleotides