According to previous research the lipid peroxidation process has a significant role in mercury toxicity. Since glutathione peroxidase (GPX) and superoxide dismutase (SOD) play a significant role in erythrocyte antioxidative defence, it is very important to determine their activity in occupationally exposed workers. The aim of this study was to assess the activity of antioxidative enzymes in the erythrocytes of workers occupationally exposed to mercury. We compared a group of 42 workers exposed to elemental mercury in a chloralkali plant (Hg group). The control group (C group) consisted of 75 subjects employed in lime production who had never been exposed to mercury or any toxic substance. The GPX activities in erythrocytes were significantly lower in the Hg group than in the control group (Hg group, 9.05 +/- 7.52 IU/gHb; C group 15.54 +/- 4.85 IU/gHb; p < 0.001). Also, SOD activity in the erythrocytes of workers occupationally exposed to mercury was significantly lower than in the control group (Hg group, 1280.7 +/- 132.3 IU/gHb; C group, 1377.9 +/- 207.5 IU/gHb; p < 0.006). The concentrations of mercury in blood were significantly higher in the Hg group compared to the control group (Hg group, 0.179 +/- 0.040 micromol/l; C group, 0.023 +/- 0.011 micromol/l; p < 0.001). Urine mercury concentrations were also significantly higher in the Hg group than in the control group (Hg group, 23.2 +/- 11.3 nmol/mmol creatinine; C group, 2.7 +/- 0.6 nmol/mmol creatinine; p < 0.001). The concentrations of selenium in erythrocytes were almost equal in both groups examined (Hg group, 62.9 +/- 8.72 microg/l; C group, 65.8 +/- 10.57 microg/l). Also, in the Hg group there were increased levels of erythrocyte malondialdehyde (Hg group, 138.58 +/- 33.85 micromol/l; C group 105.21 +/- 49.62 micromol/l; p < 0.001). On the basis of previous results, it can be concluded that occupational exposure to elemental mercury leads to increased lipid peroxidation in erythrocytes. Also, it can be postulated that this exposure leads to decreased activity of GPX and SOD in erythrocytes.