ChEMotaxonoMiCal idEntifiCation of aCtinoBaCtErial strains isolatEd froM daMP-affECtEd offiCE Building Four actinobacterial sporulating strains have been isolated from two damp-affected office buildings. They have been identified as streptomyces sp. (three strains) and cell wall type IV actinobacteria (one strain) by the chemotaxonomical approach. K e y w o r d s: Actinobacteria, Streptomyces, chemotaxonomy, cell wall, indoor air. harmful microbes in indoor environments are a cause of public concern. Bacteria and fungi infest house and office buildings affected by dampness and the environmental conditions and microbial communities undergo continual changes resulting in different microbial populations. Microbial growth on moisture-damaged building materials is commonly associated with adverse health effects in the occupants. Microorganisms, their spores and cell wall components are biologically active agents which may cause and trigger allergy and other respiratory diseases, i.e. chronic airways inflammation [1]. Although the microbial diversity in indoor environment is high, the filamentous and sporulating fungi dominate on indoor microbiota screenings [2, 3]. Recently actinobacteria involved in biological infestation of damp buildings attract increasing interest [4]. Actinobacteria are Gram-positive bacteria, with high G+C content, filamentous microorganisms, majority of which are saprophytic soil and other environmental inhabitants. As common soil organisms they easily colonize water-damaged building materials and may emit toxic-metabolites isolated from the indoor environment of a building where the occupants suffered building-related ill-health symptoms [5]. The aim of present studies was identification of sporulating bacterial strains isolated from wall surface of damp-affected office building in Warsaw (Poland), by means of chemotaxonomical approach. Materials and methods Bacterial strains L1, L2, W3, and W4 were isolated from the wall surface of damp-affected office building in Warsaw, Poland. The isolates were cultivated aerobically on medium "79" in 37 °C for 48 hours. Bacterial biomass was collected by centrifugation in 7000 rpm, after repeated washing