Microscopic fungi in the indoor environment present a serious health risk for people living in affected buildings. The potentially toxic ascomycete genus Chaetomium is supposed to be the third most frequent indoor fungal contaminant. Its brief mycological, toxicological and ecological characterization is given. The work was aimed at in vitro study of toxicity of endo- and exometabolites of 14 strains of Chaetomium spp., including 4 strains of Ch. globosum, isolated from mouldy buildings in Slovakia and Denmark, and 3 Ch. globosum strains from the Czechoslovak Collection of Microorganisms (CCM). The endometabolites of 10 isolates of Chaetomium spp. were active: 7 isolates (41% of total strain number) stopped tracheal ciliary movement of 1-d-old chickens after 24 h, 9 isolates (53%) after 48 h and 10 strains (59%) after 72 h. In the case of exometabolites, the extracts of 6 Chaetomium strains showed some ciliostatic activity: 2 isolates (12% of strains tested) after 24 h, 5 isolates (29%) after 48 h and 6 isolates (35%) after 72 h. In general, 5 isolates of Danish origin (83%) produced ciliostatically active exometabolites and 2 isolates (33%) produced such endometabolites, while only 4 strains isolated in Slovakia (50%) and 3 strains (37%) respectively did the same under experimental conditions. Most toxic metabolites were produced by Chaetomium spp. isolated from dwellings, whereas hospital isolates were not able to produce active compounds. Chaetomia as indoor contaminants can contribute to ill health of occupants of mouldy damp building