Persistent organic pollutants (POPs) are chemical substances that persist in the environment, bioaccumulate through the food web, and pose a risk of causing adverse effects to human health and the environment. The aim of the study was to assess the POP (polychlorinated biphenyls (PCBs), polybrominated diphenylethers (PBDEs), DDT and their derivatives) levels in blood serum to identify possible risk group workers. Blood serum samples (116 in total) were collected from two groups of employees — electricians, who can come in contact with PCB-containing transformer and capacitor oil, and welders, who were used as a control group. Sample purification was done by double solid phase extraction. The concentrations of POPs in blood serum were determined by gas chromatography with electron capture detector GC/ECD and recovery controlled by internal standard CB-174. None of the 116 samples contained the full range of tested POPs. However, all samples contained at least one of pesticides, and a marker PCB and mono-ortho PCB. Blood serum samples of 52% of electricians and 97.8% of welders contained non-ortho PCB compared to 84% and 74.7%, respectively, for PBDE’s. The concentrations of 18 detected PCBs, 4 detected PBDEs and 6 chlorinated pesticides and their metabolites varied in wide ranges and the differences in mean values between groups were not statistically significant (p > 0.05). The estimated concentrations of POPs correspond to the lowest levels detected in other countries. Mean concentrations of low-chlorinated marker PCBs were higher in the electrician group, suggesting that the employment sites are contaminated with PCBs, or that employees have contact with PCB-containing items.