Microbiological research of bioaerosols was carried out at the Municipal Sewage Treatment Plant in Toruń. The concentration of selected bacteria, fungi and actinomycetes in the atmospheric air was estimated in the vicinity of sand catchers, aeration chambers and maturing compost piles, as well as 100 m beyond the treatment plant. It was found that the air at the test stands showed different degrees of microbiological pollution. The largest bioaerosol emission sources were the sand catcher and the maturing compost storage facility. The total number of bacteria and fungi amounted to a maximum of 10⁴ CFU m^-3 and of actinomycetes – 10³ CFU m^-3. The bacteria of the genus Pseudomonas (fluorescent subgroup) occurred at all the stands throughout the study except December. The number of Escherichia coli and bacteria of the genera Enterococcus and Salmonella remained at the very low level of about 10¹CFU m^-3, and of all these bacteria only fecal streptococci D-type were isolated at stand 4 (beyond the treatment plant). On the basis of the research carried out and the results obtained at the control stand one may conclude that the test facility does not pose a hazard in respect of the tested bacteria emission.