The paper discusses issues in the hydrometallurgical production of tungsten (W) and molybdenum (Mo) salts and oxides of concern to industrial hygiene. The technology used is briefly described and the main adverse factors in the industry under consideration are pointed out with particular emphasis on the pollution of the atmosphere by dust containing W, Mo and SiO2. High concentrations of irritating gases (NH3, HCl, H2S) were recorded in the air in industrial production areas and work sites. Due to existing work conditions, dust induced fibrosis and a high level of chronic afflictions involving the upper respiratory tract were noted among the workers. The paper compares working conditions at two plants with different mechanized technology levels and demonstrates the importance of advanced technology in the improvement of work hygiene in the industry studied.