It has been estimated that worldwide there are more than one million full -time welders, with even more workers welding intermittently. For 15 years there has been increasing interest in the effects of welding fumes on the health of these workers. Medical studies in epidemiology have reported a higher incidence of respiratory illness among welders. Reported effects range from bronchitis, airway irritation, metal fume fever and chemical pneumonitis to lung function changes and lung cancer. Most welders know to reduce welding fume exposure whenever possible. Nevertheless, there is relatively little specific, quantitative data revealing how welding fumes affect the lungs. According to this study, welding fumes generated from different electrodes produce different lung responses and are cleared from the lungs at different rates. It was necessary to use a very large dose to elicit any response. Doses typical of those experienced by welders on a daily basis showed no response under these tests. Using higher doses, the stainless steel spray transfer (ss -Spray) fume was more toxic and was retained in the lung longer than mild steel fumes. Unlike silica, it appears that the SS-Spray particles are eventually cleared from the lungs and thus, the potential for toxic effects in the lungs is low if fume exposure ceases or if doses are reduced. Mild steel fumes induced a similar response as iron oxide, considered only a nuisance and nontoxic.