The concentration of airborne endotoxins and microorganisms in livestock buildings (cattle, pig, poultry) was surveyed in four European countries (England, The Netherlands, Denmark and Germany). Measurements were made during the day and night. The endotoxin concentrations were determined from dust samples separated into inhalable and respirable fractions. Airborne microorganisms were classified as total bacteria, Enterobacteriaceae and total fungi. The lowest endotoxin concentrations were found in cattle houses. The highest concentrations of endotoxin were measured in poultry houses, especially percheries, with an overall mean of 692 and 49 ng/m3 for inhalable and respirable fractions, respectively. Endotoxin concentration was usually higher in the day than at night. These concentrations give cause for concern for the health of stockmen working in such buildings. The corresponding mean emission rates from poultry houses were 678 and 43 μg/h (500 kg) liveweight, respectively, 51 and 6 μg/h (500 kg) liveweight from pig buildings and 9 and 1 μg/h (500 kg) liveweight from cattle houses. A new automated bioaerosol sampler was developed, which allows remote, independent sampling of airborne microorganisms. Its principle of operation is similar to a slit sampler: airborne microbes are collected by impaction on an agar surface. Most measurements of airborne microorganisms were made in Germany. The indoor concentration of total bacteria was 6.43 log colony-forming units (cfu)/m3 in broiler houses, 5.1 log cfu/m3 in pig buildings and 4.3 log cfu/m3 in cattle buildings. During the day, the overall concentration of Enterobacteriaceae ranged between 3 and 4 log cfu/m3. The mean fungi concentration for cattle was 3.8, for pigs 3.7 and for poultry 4.0 log cfu/m3 during the day. Slightly lower concentrations were measured at night. No significant correlation was found between the concentrations of endotoxin and Enterobacteriaceae. The highest emission rate of total bacteria and fungi was measured for broilers, i.e. 9.5 and 7.7 log cfu/h (500 kg) liveweight, respectively. Buildings for laying hens had the highest mean emission rate of 7.1 log cfu/h (500 kg) liveweight for Enter obacteriaceae.