CYTOGENETIC BIOLOGICAL DOSIMETRY IN THE LIQUIDATORS OF CHERNOBYLACCIDENT. When human body exposes to ionizing radiation, the most important kind of damage are double strand breaks of DNA. Misrepair of the damages can lead to morphological changes inchromosomes known as chromosomal aberrations. Measurement of chromosome aberrations inblood peripheral lymphocyte cells has been applied to assess dose received by potentiallyoverexposed people and estimate risk for health effects in radiation or nuclear accident cases.Dicentric and translocation are the most important types of chromosome aberrations in biologicaldosimetry or biodosimetry which is usually used when there is no physical dosimetry available or when irradiation dose needs to be confirmed.The cytogenetic screening had been carried out inChernobyl accident for biological doses estimated from dicentric and translocation yields inliquidators (clean-up workers). This paper reviews the cytogenetical biodosimetry application inChernobyl accident liquidators that has proved the worth of the method. Absorbed dose estimatesderived using cytogenetic data and dose response calibration curves are based on the assumption that all individuals have equally respond to radiation