The aim of the study was a mycological assessment of bioaerosol formingduring conservative dental treatment, taking into account concentration and type of fungal microflora,and evaluation of the influence of DUWL disinfecting protocol on the fungal contamination of the bioaerosol.The research was conducted on 25 operative sites located in public dental clinics. The air containedin the space between a patient and a dentist during conservative dental treatment with the use of a high-speedhandpiece was examined. Air samples were taken using the portable RCS PLUS Air Sampler (BIOTEST AG, Dreieich,Germany) and ready-to-use agar YM Strips for yeast and mould fungi culture. The volume of the sampledair was 100 litres. Before disinfection, the concentration of fungi in the collected air samples at individualoperative sites ranged from 4 x 10(1) cfu/m3 to 34 x 10(1) cfu/m3. The most common species was Penicilliumherquei (62.17% of the total count), followed by other fungi: Alternaria alternata - 12.68%, Penicilliumroseopurpureum - 9.41%, Rhizopus nigricans - 5.93%, Aspergillus terreus - 3.89%, Geotrichum candidum- 2.25%, Aspergillus glaucus group - 2.04%, Cladosporium cladosporoides - 1.23% and Penicillium diversum- 0.41%. The concentration of Penicillium herquei at individual operative sites ranged from 0 to 34 x10(1) cfu/m3, mean 121.6 cfu/m3, Penicillium roseopurpureum - from 0 to 11 x 10(1) cfu/m3, mean 18.4cfu/m3 and Alternaria alternata - from 0 to 18 x 10(1) cfu/m3, mean 24.8 cfu/m3. After disinfection,like before disinfection procedures, the prevailing species of fungi were: Penicillium herquei, Penicilliumreseopurpureum and Alternaria alternata, which amounted to 62.6%, 18.28% and 11.36% of the isolated fungi,respectively. The recorded levels of total airborne fungi were lower after DUWL disinfection comparedto those before disinfection.