The liver is the critical organ in the case of a long-term occupational or environmental exposure to heavy metals and tobacco smoke. In diagnostics of liver damage useful are the methods which determine the activity of enzymes such as gamma-glutamyl-transferase (GGT). GGT is present in the liver and bile duct. In the serum is mainly from hepatic. Clinical studies have shown that GGT is highly sensitive indicator of liver damage. Increased activity is observed in acute and chronic liver disease, biliary tract, pancreas. Strong stimulus of growth in serum is alcohol consumption, exposure to heavy metals (including lead, cadmium), dioxins and pesticides. The aim of this research was to assess the influence of occupational exposure of copper-foundry workers to heavy metals (arsenic, cadmium, lead) on activity of gamma-glutamyltransferase in blood. The investigations were performed in blood and urine of 166 subjects: 101 male copper smelters and 65 non-exposed male subjects. The study protocol was approved by Local Bioethics Committee of Wroclaw Medical University (KB No: 469/2008). The data on smoking which had been obtained from a direct personal interview were verified by determination of serum cotinine concentration. Biological material collected from the control group and the smelter workers was divided into groups of non-smokers, those who smoked less than 20 cigarettes a day and those who smoked 20 or more than 20 cigarettes a day. The concentrations of lead and cadmium were determined in whole blood, whilst the level of arsenic was determined in urine. The activities of GGT were determined in blood. We have observed a significant increase in the concentrations of lead, cadmium and arsenic in blood and urine of persons from control group who smoked 20 or over 20 cigarettes a day in comparison to the non-smoking persons from control group, which suggest, that tobacco smoking increase the heavy metals concentrations in the organisms. The results showed a 9-fold increase in the concentration of lead and 10-fold elevation of arsenic level in all groups of smelters in comparison to the appropriate control groups. The highest cadmium, lead and arsenic concentrations were observed in blood and urine of copper foundry workers who smoked over 20 cigarettes per day. Occupational exposure to heavy metals resulted in an increase of GGT activity in all groups of smelters in comparison to corresponding control groups. The highest value of GGT was observed in serum of smelters who smoked 20 or over 20 cigarettes per day and it was more than 2-fold higher than the activity observed in non-smokers in the control group. Smoking 20 or more 20 cigarettes per day also increases the blood GGT activity of smelters and control group compared to the nonsmoking smelters and non-smoking control group, appropriate. The study was shown that occupational exposure to heavy metals can toxic effects on the structure of the liver, which confirms the increased of GGT activity.