Welding fumes are classified as possibly carcinogenic to humans (Group 2B) by the International Agency for Research on Cancer. In the current study, blood and urine concentrations of aluminum (Al), cadmium (Cd), cobalt (Co), chromium (Cr), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) were monitored by inductively coupled plasma-mass spectrometry (ICP-MS) in 30 welders and in 22 controls. In addition, DNA damage was examined in the lymphocytes of these subjects by the alkaline Comet assay. Two biological samples were taken from the welders at the beginning (BW) and at the end (EW) of a work week. In controls, collection of samples was limited to BW. Blood concentrations of Cd, Co, Cr, Ni, and Pb were higher in the welders than in the control group while higher concentrations of Al, Cd, Co, Cr, Ni, and Pb were detected in welder urines. There was no significant difference in the metal concentrations for the BW and EW welder samples. Increased levels of DNA damage were found in lymphocytes from welders as compared to the controls, and 20/30 welders had higher levels of DNA lesions in the EW than in the BW samples. Age had a significant effect on DNA damage in the control group. Spearman's rank correlation analysis indicated that there were positive correlations between blood concentrations of Al, Co, Ni, and Pb and the levels of DNA damage. A negative correlation was found between DNA damage and Mn in blood, while there was a positive correlation between urinary Mn concentration and DNA damage. These data indicate that occupational exposure to welding fumes increases DNA damage in lymphocytes. Environ. Mol. Mutagen. 47:284-295, 2006. © 2006 Wiley-Liss, Inc.