Introduction: Chronic benzene exposure has a detrimental effect on the hematopoietic system, disturbs its genetic material through the enhancement of oxidative DNA damage, increase the incidence of chromosomal aberrations that may result in direct hematotoxicity and an initiating step for leukemogenesis. Aim of work: To study the adverse impact of occupationally benzene exposure on peripheral blood cells, oxidative DNA damage and gene translocation of peripheral mononuclear blood cells through measurement of plasma 8-hydroxy-2'-deoxyguanosine (8-OHDG) levels and detection of RUNX1-RUNX1T1 translocation “t(8;21)". Materials and methods: The study was carried out on 91 subjects classified into two groups; group (I) occupationally benzene-exposed (57 subjects), which was subdivided into two subgroups: (A) “ smokers" (No=41) and (B) “non-smokers" (No =16), Group (II) a control group and is also subdivided into two subgroups, (C) “smokers" (No =13) and (D) “non-smokers" (No =21) apparently healthy individuals not occupationally exposed to benzene. Data was collected using a specially designed questionnaire covering socio-demographic data, personnel and occupational histories. Investigations were done including: Blood cell count (CBC), examination of peripheral blood smears, Plasma 8-OHdG was measured by ELISA system, Translocation (8; 21) was detected. Working index and Smoking index were also calculated. Results: there was a significant increase in the plasma  levels of 8-OHdG in the occupationally benzene-exposed group both smokers and non-smokers and in control smokers in comparison to the control non-smoker individuals. The percentage of RUNX1-RUNX1T1 translocation was (3/41) 7.3% in occupationally benzene-exposed smokers, (1/13) 7.7% of control smokers, while it was negative among the non-smokers individuals either exposed to benzene or not.
Conclusion: There was an increase of plasma 8-OHDG levels and increased incidence of RUNX1-RUNX1T1 translocation t (8; 21) of mononuclear peripheral blood cells due to chronic benzene-exposure either occupationally or through tobacco smoking with obvious dysplastic features of peripheral blood cells.