This study was performed to study the efficiency of a local ventilation system, installed in dental laboratories, and of two types of protecting face masks. The dust originating from the workpiece as well as from the wheels and stones was collected on air filters in the cutting cycle during coarse and fine grinding, and in the subsequent polishing procedures of each specific dental material. The efficiency of the ventilation system was measured on the basis of weight reduction of dust in the breathing air at a distance about 20-40 cm from workpiece. The results were as follows: 1. Use of the local ventilation system reduced the amounts of respirable dust to an average level of 21.4%, although the efficiency of the local ventilation system varied depending upon materials used. 2. Mounting a nozzle on the tube improved the efficiency of the ventilation system considerably. The efficiency of the local ventilation system also increased as the workpiece was closing to the tube inlet. 3. With or without the local ventilation system, the distance between the position of the workpiece and sampler greatly affected the dust level. 4. The face masks covering the sampler improved the efficiency of the ventilation system considerably.