Mechanical screen printing causes occupational problems, due to the evaporation of solvent vapours in the workplace air. Laboratory experiments were made in order to find out the efficiency of the local exhaust ventilation of a semiautomatic press with the help of capture degree and occupational hygiene efficiency. To find out the efficiency of the different local ventilation systems, they were tested in laboratory conditions. There were 10 stationary sampling points around the printing machine, in the breathing zone and in the ventilation ducts where the solvent vapour concentration was measured. In the laboratory four different local exhaust systems were studied. In addition to this, the efficiency of a canopy hood used in a screen printing plant was also studied. Moreover, the influence of a supply air terminal device on the air quality was examined. The local exhaust systems described in the report improved the air quality when using general ventilation. The efficiency of correctly designed local exhaust systems is 80 - 95 per-cent. Thus the concentrations in the workroom air decrease to 1/5 - 1/20 of the concentrations achieved by general ventilation.