Many studies showed that occupants of mouldy dwellings might have physical impairments because of inhalation of mould components (live or dead conidia and mycelial fragments), usually manifested as irritations of respiratory tract, conjunctivitis or systemic manifestations. These symptoms could be attributed to allergic and/or toxic effects of mould cell wall components and especially mycotoxins (Flappan et al. 1999; Schulz et al. 2004). Secondary toxic metabolites (e.g. satratoxins, aflatoxins, ochratoxin A and sterigmatocystin), which are produced by Stachybotrys, Aspergillus and Penicillium species, exerted their various toxic effects in cell cultures as well as in vivo toxicity studies (Piecková and Jesenská 1999; Bünger et al. 2004; Hossain et al. 2004; Pieckováet al. 2004; Schulz et al. 2004). In this study, the most abundant fungi originated from wall scrapes were species of Aspergillus and Penicillium. These species can grow at aw values below 0·8, and thus were found more frequently on building materials. Secondary colonizers including Alternaria spp. and Ulocladium spp. together with Absidia spp. and Mucor spp. constituted the 8% of recovered mould isolates. Cladosporium spp., Trichoderma spp. and Rhizopus spp. were found in three samples while C. globosum was recovered from the only one sample. Studies in Slovakia also showed that the most frequently isolated species from wall scrapes were Penicillium spp., Aspergillus spp. (A. versicolor, A. flavus), as well as Cladosporium spp. (C. sphaerospermum, C. cladosporioides) (Piecková and Kunová 2002). Many literature reports focused on S. chartarum because of production of highly toxic metabolites, such as satratoxins. However, this species is not frequently isolated from the walls, and it was not found in this study because it usually grows in water-damaged dwellings at high aw values (Piecková and Jesenská 1999), from which we did not collect our scrapings. Two strains of S. charatrum employed in this study were found in Slovakia among seven isolates recovered from 147 collected samples of wall scrapes, house dust and air samples (Pieckováet al. 2004). All of these findings indicate a certain health hazard during long-lasting exposure to airborne microfungi particles because of toxic effects of mycotoxins and other toxic metabolites, which could be found in them. Recently, there has been considerable interest in essential oils with antifungal activity, which are more acceptable, ecological safe and less hazardous than disinfecting synthetic compounds that are used in air cleaning. Essential oil of thyme (Thymus vulgaris L.), used in this study contains p-cymene (36·5%), thymol (33·0%) and 1,8-cineole (11·3%) as main components. The thyme essential oil exhibited strong antifungal activity against isolated microfungi with MIC values ranged between 1·60 and 50·20 μg ml−1, and MFC values ranged between 1·60 and 116·6 μg ml−1, respectively. Essential oils from other Thymus species, such as Thymus eriocalyx and Thymus × porlock, which contained thymol as major component (63·8, 31·7%), exhibited fungistatic (250 ppm) and fungicidal activity (500 ppm) on aflatoxigenic A. parasiticus strain (Rasooli and Owlia 2005). In addition, essential oil of Thymus spathulifolius, which contained similar amount of thymol (36·5%) as essential oil used in this study, suppressed the growth of Trichophyton spp., Fusarium spp., Penicillium spp., Rhizopus spp., Alternaria spp. and Aspergillus spp., with MICs ranged between 31 and 250 μg ml−1 (Sokeman et al. 2004). The thymol itself exhibited approximately three-times stronger inhibition than essential oil of thyme. MIC values of thymol were between 1·60 and 6·72 μg ml−1, and MFC values were between 3·20 and 13·74 μg ml−1, respectively. According to MIC values of both essential oil of thyme and pure thymol, the most sensitive was C. globosum while the most resistant were species of Mucor. Thymol expressed strong fungicidal activity against opportunistic yeasts Cryptococcus neoformans and Candida spp., as well as against dermatophytes (Viollon and Chaumont 1994; Pauli 2001). Few studies reported on antifungal activity of pure thymol as well as p-cymene and 1,8-cineole. Pure p-cymene and 1,8-cineole were much less effective against Aspergillus spp. and Penicillium spp., (MIC values were ≥4 or 8% v/v), when compared with pure thymol (Hammer et al. 2003). However, thymol and p-cymene exhibited strong antifungal activity against number of Candida spp., with similar MICs ranged 0·08 and 0·32% (v/v), while 1,8-cineole was effective only in higher concentrations (5–10% v/v). In addition, the combination of thymol and p-cymene as well as thymol and 1,8-cineole showed synergistic antifungal effect against Candida spp. (Pina-Vaz et al. 2004). According to these observations, we can speculate that strong antifungal activity of thyme essential oil could be attributed to thymol itself or could be a result of synergism of other main components in the oil. Vaporous phase of essential oil of thyme (82 μg l−1) employed in this study suppressed the development of fructification organs and sporulation and exhibited the sporocidal effect on sporulating cultures after 2 months of exposure of tested moulds. Rakotonirainy and Lavédrine (2005) reported on fungistatic but not fungicidal activity of linalool (295 and 415 ppm) after 21 days of exposure of mouldy books in glass chamber, volume 10·2 l. Comparing with these results, vaporous phase of essential oil of thyme happens to be more effective. Rasooli and Owlia (2005) showed that main target of thyme oils were cell wall and cell membrane of A. parasiticus. The plasma membrane was irregular, dissociated from cell wall, invaginated and associated with the formation of lomasomes, which were found in fungi treated with imidazole components. At low concentrations, phenolic lipophilic compounds such as thymol altered the microbial cell permeability permitting the loss of macromolecules. Exact cause–effect relation for the mode of action of phenols has not been determined, but they may inactivate essential enzymes, react with cell membrane proteins or disturb genetic material functionality (López-Malo et al. 2005). From this point of view, essential oil of thyme, which is rich in thymol and other antifungal components, could be used for disinfection of mouldy walls in the dwellings in low concentration.