This study aimed to find out the dependence of myeloperoxidase content in patients living in the environmentally unfriendly region of Kazakhstan (Taraz), on the PCBs content in the air. During this study, 324 patients were examined to solve the clinical problem. The content of myeloperoxidase fluctuated significantly depending on the age of the experimental subjects. Statistically significant increase in the enzyme was observed in 23.0% of children aged 6-7 years, 33.4% of adolescents aged 14-17 years and 39.2% of adults aged 50-59 years. At the same time, significantly low content of myeloperoxidase was largely verified in children, adolescents, as well as in groups of the experimental subjects aged between 18-29 and 30-39 years. The largest number of people with low activity of myeloperoxidase was observed in groups aged between 40 and 49 years, which made 77.5% of the total. Research results showed significant inverse correlation between the low activity of myeloperoxidase and the PCBs concentration, which ranged from r = -0,55 to r = -0,91 (p <0,05). Therefore, the most significant correlation between the laboratory and hygienic indices was detected among subjects aged between 50-59 years (r = -0,9).