In this work we present our data about the protective effect of the newly synthesized compound 1-(4-fluorphenyltioureido)-4-methyl-piperazyne (FTMP) against high doses UV-C irradiation using human lymphocytes in vitro as a model system. The endpoint used was chromosome aberrations. The genotoxic effect of different UV-C doses in the range from 10 J/m2 to 200 J/m2 was evaluated. Studying the protective effect of FTMP, it was obtained that a low, adaptive concentration (10(-6) mol/l) applied before harmful doses of UV-C irradiation (100 J/M2 and 150 J/M2) induces the yield of chromosome aberrations lower than theoretical, estimated as a sum of single effects of both agents. A tendency for reducing the damage effect of UV-C irradiation was established. The effect is the most clear when a 4-hour interval between the treatments was used. The mitotic index was not affected. These results pointed out the ability of FTMP to decrease the damaging effect of UV-C irradiation in this type of cells and possess the potential to induce the adaptive response against the damaging effect of UV-C irradiation.