The microbial quality of the outdoor air in Poznań (Poland) was estimated by sedimentation method in the years 2002 and 2003. Microorganism concentration was high, the average monthly number of bacteria in 2002 often exceeded 3,000 cfu/m³ and reached in the summer 13,000 cfu/m³. At least 50% of airborne microorganisms were filamentous fungi. The concentration of two allergenic fungus genera Cladosporium and Alternaria estimated by Burkard trap reached in summer months 11,000 spores/m³ in 2002 and 16,000 spores/m³ in 2003. Airborne microorganism concentrations varied and changed with seasons and years, depending on sampling site and method of determination.