The erythrocyte antioxidant system (superoxide dismutase, SOD; catalase, CAT) and lipid peroxidation (malondialdehyde, MDA) in the erythrocyte membrane were studied in workers continously exposed to welding fumes and gases, which are thought to be oxidant pollutants. Thirty-five welders using the manual metal arc method on stainless steel and 30 controls were studied. Plasma chromium (Cr), manganese (Mn), and cupper (Cu) levels were determined by atomic absorption spectrophotometer (AAS). The erythrocyte antioxidant system activity and lipid peroxidation in the erythrocyte membrane were evaluated. Not only the possible effects of welding fumes but also the effects of smoking were considered. The plasma concentrations of Cr, Mn, and Cu for the exposed welders were significantly higher compared to the control subjects (p < 0.001, p < 0.01, p < 0.001, respectively,). The erythrocyte CAT (p < 0.05) and SOD (p < 0.05) enzyme activities were significantly higher in the welders but there were not any significant changes in the MDA levels which reflect the lipid peroxidation in the erythrocyte membrane (p > 0.05). Smoking has increased the SOD activity in both controls (p < 0.05) and welders (p < 0.01) and increased the CAT activity in control subjects (p < 0.05). Moreover, regardless of smoking, there were some significant correlations between the duration of the exposure to welding fumes and antioxidant defence system (SOD: p < 0.05; CAT: p < 0.05). The synergistic effects of smoking and other risk factors (welding fumes and gasses), which had been shown previously by some clinical data should also be taken into account. As a consequence, the welders should be warned and informed of the synergistic effects of smoking on the adverse effect of welding fumes and gases. (c) 2007 Elsevier GmbH. All rights reserved.