Air samples from ten conventionally ventilated operating rooms were taken simultaneously by the sedimentation method and by the air sampler. The investigations showed that the number of colony forming units per cubic metre obtained with the sedimentation method was, on average, lower than those found with the impactor sampler (p 0.03). The most commonly isolated pathogenic species of bacteria were: Staphylococcus aureus, Enterococcus spp., Streptococcus z gr. B, Pseudomonas aeruginosa, Acinetobacter lwoffii and Alcaligenes faecalis. The dominant fungal species were Penicillium spp. and Cladosporium spp. When Tryptic Soy Agar with neutralising agents was used, the number of detected airborne micro-organisms was greater (p 0.01).