Gas metal arc welding is a widely used method in a lot of industrial areas as it is cheap and produces high quality results. In the present study, peripheral blood lymphocytes of 23 welders and 25 non-exposed subjects were monitored for cytotoxicity. Information regarding the subjects' ages, smoking habits, alcohol consumption, duration of exposure, and medicine usage was recorded. According to the results, mitotic index (2.278 +/- 1.325) of the welders was higher than that of those non-exposed (0.956 +/- 0.616) (P < 0.01). There was no significant difference between mitotic index rates of smoking and non-smoking subjects. In contrast, there were significant differences between non-exposed subjects and welders for both smoking and non-smoking (P < 0.05). It was found that as the time of exposure to welding fumes increased so did the mitotic index rates (P < 0.05). Both a positive correlation in welders and a negative correlation in non-exposed subjects were observed between mitotic index frequency and age. In the light of the results obtained, it is advised that welders who work with gas metal arc welding be instructed and necessary protective measures be taken because of the risk caused by metal arc welding fumes.