Microbiological air sampling was performed in one fiberboard factory and two chipboard factories located in south-eastern Poland. It was found that the levels of bacteria, fungi, dust and bacterial endotoxin in the air of examined facilities were high during initial stages of the production cycle (shredding of waste wood, storing of chips) and then sharply decreased during further stages of this cycle (forming and formatting of the boards). In the fiberboard factory, the concentration of airborne microorganisms at the initial stages of production cycle was 71.8-95.2 x 10(3) cfu/m3 and dropped in further stages to the level of 8.4-17.5 x 10(3) cfu/m3. Fungi (mostly Aspergillus fumigatus and Penicillium spp.) were prevailing microorganisms in the air of the fiberboard factory, forming 46.0-87.3% of the total airborne microflora. The concentrations of microorganisms in the air of the chipboard factories were significantly lower compared to the fiberboard factory (p<0.05). During initial stages of production cycle they were within the range of 12.9-101.5 x 10(3) cfu/m3, while during forming and formatting of boards within the range of 5.3-12.4 x 10(3) cfu/m3. On average, the most common microorganisms in the air of the chipboard factories were corynebacteria (mostly Arthrobacter spp. and Corynebacterium spp.) which formed 24.4-64.6% of the total microflora. The values of the respirable fraction of airborne microflora in the fiberboard and chipboard factories varied within a fairly wide range and were between 20.5-91.1%. Altogether, 38 species or genera of bacteria and 16 species or genera of fungi were identified in the air of examined factories, of which respectively 14 and 9 species or genera were reported as having allergenic and/or immunotoxic properties. The concentration of bacterial endotoxin in the air of examined factories was greatest, similarly to the concentration of microorganisms, during the initial stages of the production cycle: 103.1-1974.0 EU/m3 in the fiberboard factory, and 3.2-217.4 EU/m3 in chipboard factories. In conclusion, the workers of fiberboard and chipboard factories may be exposed during the initial stages of the production cycle (shredding of waste wood, storing of chips) to high levels of airborne microorganisms and endotoxin posing respiratory hazard.