Rationale: Oxidative stress is believed to play a key role in the development of welding-induced disease. Objectives: This study investigated the effects of welding fumes exposure on correlates of oxidative stress in the serum of asymptomatic shipyard welders. Methods: Blood samples from 197 male welders and 150 unexposed male office workers were analyzed for manganese and lead. Serum was assayed for protein, albumin, total antioxidant status (TAS), manganese superoxide dismutase (Mn-SOD), aconitase, glutathione peroxidase (GPx), heat shock protein 70 (Hsp70), isoprostane, and reactive oxygen species (ROS), using ESR and chemiluminescence (CL). Comparisons between welders and controls on biomarkers of oxidative stress were made, and evaluated for the effects of age and smoking. Associations between blood levels of manganese and lead and biomarkers were also explored. Results: Welding was associated with increases in serum protein, GPx, aconitase, TAS, and isoprostane levels compared to controls. These group differences were not altered by age or smoking. In welders and controls, age was significantly associated with changes in albumin, TAS, CL, GPx, and Mn-SOD. In welders and controls, smoking resulted in a decrease in GPx, and a significant interaction between smoking and CL. There were significant correlations between manganese levels in welders' blood and CL, GPx, Mn-SOD, and between lead levels and albumin, TAS, GPx, and Mn-SOD. Conclusions: These results document that exposure to welding can cause changes in serum biomarkers of oxidative stress which may be valuable in clinical monitoring of disease development and assessing whether further reduction of worker exposures are needed.