Growing evidences indicate that fungi like Aspergillus in indoor environment can pose serious threat to public health. Many professions and lifestyles like closed-room living, expose healthy individuals to pathogenic Aspergillus, resulting invasive infection in some of them, which may be life-threatening. Inhalation can show the way to invasive aspergillosis in immuno-compromised individuals and respiratory allergy in healthy ones. Although we have been hindered by profound ignorance of the biology of these important environmental contaminants, evidence for indoor mould exposure and exacerbations of respiratory diseases is strong. These evidences pressurize us to typify the pathogenic species in the indoor air by molecular methods and to redesign our hygienic strategies which so far were targeting mostly the pathogenic bacteria.