Agricultural work, particularly livestock farming, is considered to be a notable risk factor for occupational diseases. Endotoxin as a major component of organic dust causes adverse health effects of the airways among farmers. Endotoxin concentrations in airborne and settled dust were measured in modern, naturally ventilated animal houses for different species. Median values of airborne inhalable endotoxin ranged from 16.9 EU/m³ for dairy cattle, 557.9 EU/m³ for beef cattle, 668.7 EU/m³ for pigs, 463.2 EU/m³ for laying hens, to 1,902 EU/m³ for turkeys. The endotoxin levels in settled dust followed the same pattern as the airborne samples. The concentrations were lower than in previous studies, but the proposed Dutch endotoxin threshold (50 EU/m³) was exceeded in most cases. Thus, endotoxin levels in modern animal houses still give concem for health and further reduction of endotoxin exposure in animal houses is desirable