In order to study the effects of welding fume on ventilatory function, forced expiratory spirogram was performed on 563 male workers exposed to welding fume in motor vehicles industry and 589 male control workers. Ventilatory indices such as forced vital capacity (FVC), forced expiratory volume in one second (FEV(1)), the ratio of one-second forced expiratory volume to forced vital capacity (FEV(1)%= FEV(1)/FVC) and maximal mid-expiratory flow(MMF) were obtained by analyzing forced expiratory spirogram which were measured by Vitalograph in standing position. The results were as follows: 1. Mean values of FVC, FEV(1), FEV(1)%, and MMF expressed as percent of the predicted were significantly lower in exposure group than in control group. 2. No significant differences for mean ventilatory indices were demonstrated between smokers and nonsmokers both in exposure group and control group. However, mean MMF of welders tended to reduce in smokers (77.4 %) than in nonsmokers (82.4 %). 3. In exposure group mean FEV(1) was significantly lower in more than 20 years than those of control group. However, mean MMF, FEV(1)% were significantly reduced with increasing exposure duration compared to control group, indicating 90.8 %; and 62.2 % of the predicted in more than 20 years group. 4. In exposure group workers with obstructive ventilatory impairment (7.5 %) was markedly higher than that with restrictive ventilatory impairment (2.0 %). 5. In exposure group the proportion of workers with low ventilatory indices was' the highest in MMF (26.8 %), and followed by FEV(1)(11.9 %), FEV(1)%(7.6 %) and FVC (2.1 %) in descending order. Workers with low MMF and PEV^% were significantly increased with increasing exposure duration compared to control group, indicating 64.3 % and 32.1 % in above 20 years group. With the above considerations in mind it suggested that the exposure to welding fume be associated with reduced pulmonary function and obstructive ventilratory impairment, increasing exposure duration be associated with reduced pulmonary function, and MMF be the most sensitive index in the evaluation of venfcilatory impairments of workers exposed to welding fume.