OBJECTIVES. Chromosomal aberrations (CAs) are the one of the most sensitive biomarikers of biological effects from the hazardous environmental exposure. In this relation the comparison of cytogenetical indices in persons, exposed to the complex of factors of chemically hazard enterprises, with the presence of occupationally caused diseases seems to be very perspective for the understanding of the role of the contribution of genotoxical impact of occupational factors into staff morbidity. METHODS. Cytogenetical analysis was performed in 138 employees of chemically hazardous enterprises, including 84 patients, who need for establishment of the causation of diseases with the work in conditions of chemical plant and 54 persons without need for hospitalization according to results of the previous examination. Comparison group was consisted of 55 persons. There was performed the comparison of cytogenetical indices and commensuration of ratios of persons with individual high CAs levels and also carriers of exchange aberrations of chromosomal type in different groups of examined cases. RESULTS. There was shown statistically significant increase of the rate of CAs level including unexpectedly high level of dicentric and ring chromosomes in the group of 84 hospitalized patients. There was revealed statistically significant gain in the share of persons with CAs rate more then 5% (p0.01) and/or carriers of dicentrics and ring chronosomes (p0.5) in this group.It is possible to suggest that genotoxical impact plays a significant role in the mechanism of appearance of diseases etiologically related with the work on the enterprise of the high chemical risk.