[en] The aim of this study is to find out if the exposure age and the age of testing affect the radiosensitivity of peripheral blood leukocytes. The Unscheduled DNA Synthesis (UDS) and Protein Synthesis (PS) are applied. The exposed workers have an occupational experience of 2 to 20 years, an internal control group from Kozloduy NPP administration staff and external control group from Sofia region. Intensity of both induced repair synthesis and normal DNA synthesis is defined in short-term culture of whole blood after incubation with ³H-thymidine for 2 hours in either the presence or absence of hydroxyurea. The Pauly's method is used for determination of PS by comparison of incorporation of ¹⁴C-valine for 2-hour incubation at 37 ⁰C after exposure to 2 Gy gamma-rays to ¹⁴C-valine incorporation at the same conditions but without irradiation. The dye exclusion test for a cell viability determination is applied. In chronic exposure conditions UDS increases progressively with the age of the tested NPP workers with dose low than 20 mSv (< 1 mSv/year). For the persons with dose >20 mSv (from 1 to 12 mSv/year) the level of UDS is constant. PS changes depend on age: exposure age and age at the moment of investigation. When the person starts to work at an age over 45 years (for doses > 20 mSv), an enhancement of chronic radiation exposure impact ai observed. The preliminary results indicated that UDS and PS are statistically higher for NPP workers. The magnitudes of the radiosensitivity in peripheral leukocytes vary between blood samples form different age groups. (authors)