Arsenic (As) is a human carcinogen with a high risk of cancer development in people exposed to it in industry and in the general environment. The mechanisms involved in arsenic carcinogenesis are still unknown. There is a hypothesis that reactive oxygen species (ROS) may play an important role in arsenic carcinogenesis. 8-hydroxydeoxyguanosine is a nucleotide form that results from oxidative DNA damage, which causes mutation in vitro and in vivo. So the occurrence of 8-OHdG (8-hydroxy-2’-deoxyguanosine) has been used to study damaging effects on DNA of ROS. The aim of our study was to investigate whether oxidative damage of DNA, determined by elevated serum levels of 8-OHdG, could be observed in workers occupationally exposed to As and lead (Pb), and environmentally to cadmium (Cd). According to the aim, a group of 47 copper smelters, working in the copper foundry “Legnica”, and 20 matched non-exposed men were examined. Stressgen’s StressXpress DNA Damage ELISA Kit was used for detection and quantitation of 8-hydroxy-2’-deoxyguanosine (8-OHdG) in serum samples. The serum concentration of 8-OHdG was significantly higher in the study group than in the controls. No significant differences between serum 8-OHdG concentration in the group of exposed smokers, exposed nonsmokers and smoking controls were found. Moreover, no significant correlations between serum concentration of 8-OHdG and arsenic, lead and cadmium levels were observed, but people with the worst toxicological parameters showed higher 8-OHdG serum concentration. The results suggest that: 1. chronic mixed exposure to arsenic, cadmium and lead may result in oxidative DNA damage in humans; 2. 8-OHdG serum level measurement may be a useful tool for biomonitoring in the case of mixed occupational exposure to these toxic metals and increased cancer risk.