In occupational hygiene the common practice is to use dilution ventilation (MIXVENT) which ideally requires perfect mixing. Increasingly, however, displacement ventilation (DISPVENT) is being applied; ideally this involves fresh air displacing contaminated air without mixing. Keeping MIXVENT as a reference the approach of intervention was used to estimate the potential of DISPVENT for improving environmental conditions in a garment sewing plant. Air exchange efficiency of MIXVENT came to 49%. DISPVENT improved the efficiency to a level of 57%. In terms of local mean age of air DISPVENT improved conditions by a factorof 1.3. From the air diffusion effectiveness MIXVENT improved air diffusion effectiveness by a factor of 1.7, and no short-circuiting was observed. It is concluded that DISPVENT has potential for improving environmental conditions in industry.