Airborne dust concentrations in pig houses were reduced by spraying with a mixture of water and rapeseed oil (1 to 4 treatments d-1). The daily doses of oil (5 to 64 mL pig-1 d-1) were varied as the oil concentrations (5 to 20%) and the duration of the spraying time (5 to 90 s d-1) were changed. The treatment did not cause an increase of the average concentration of vegetable oil in the air. No pathological lung change in the pigs related to the treatment with rapeseed oil was found and no indication of oil resorption to lung tissues, lymph nodes, or upper respiratory systems in the pigs was seen. Long-term observations in houses for piglets, young pigs and fattening pigs at a commercial farm showed that the respirable dust was reduced by 76, 54 and 52%, respectively. No significant difference in pig performance between treated and reference groups was found. A farmer, whose lung function usually decreased when weighing fattening pigs, was not affected when the house was treated. This suggests that a substantial improvement in the working environment can be achieved by spraying a vegetable oil in pig houses.