The total mass concn. of aerial dust particles in 11 pig finishing units averaged 8.1 mg/msuperscript 3 during a 9-month survey and exceeded the 15 mg/msuperscript 3 US Occupational Safety and Health Act threshold in 13 of 88 farm visits. The av. particle number concn. from 75 samples of 1.76 to 7.01 mu m diam. particles was 11.2/ml. Total particle mass and number concn. were significantly related (P<0.10) to ventilation type, outside air temp., inside/outside air temp. difference and inside RH. Inorganic contents of aerial and settled dust were 13.2 and 14.2%, respectively.