A study on indoor air microbiological contamination in various rooms of university buildings in Poznań, Poland, is presented. Investigations were conducted in the period September-October 2002 and the same period in 2003. Air samples were taken twice a day: in the morning and in the afternoon. In all of the tested places a multiple growth of bacteria and significant increase of mould spores was observed in afternoons. The predominant bacteria and moulds isolated from investigated air samples were: Staphylococcus spp., Micrococcus spp., Serratia spp., Aspergillus spp., Penicillium spp., Rhizopus spp., Cladosporium spp. and Alternaria spp. Among these microbes the presence of pathogenic and strongly allergenic microorganisms was detected.