Moulds constitute the largest group of bacteria, prevailing both in the indoor and outdoor air. Approximately 200 000 species of moulds have been identified so far, where only a small group of around 200 may present a threat to human health. Fungi from Aspergillus species are among the moulds considered to be most pathogenic. They also constitute the group of most pathogenic moulds most frequently isolated from the environment. Over 250 types of this species are known; about 50 of them were precisely described before the year 2000 (Klich, 2009). Pathogenicity, due to their toxicity, was also documented in other species: Aspergillus fumigatus, Aspergillus flavus, Aspergillus ochraceus, Aspergillus niger, Aspergillus versicolor, Aspergillus parasiticus. Aspergillus nidulans, Aspergillus ustus, Aspergillus glaucus, Aspergillus clavatus, Aspergillus sydowii and Aspergillus terreus. Their taxonomic identification is still an open topic because of their morphological variability and ability to produce metabolites; new species which exhibit adverse health effects to humans are constantly being detected. Aspergillus lentulus is one of the recently detected species of considerable clinical importance; it reveals similarity to Aspergillus fumigatus, one of the most pathogenic fungus for humans (Balajee et al., 2005).Table 1 presents the classification of species of fungi pathogenic to humans from the Aspergillus species. The list has been created by the authors of “Atlas Grzybów Chorobotwórczych Człowieka" ("Atlas of Fungi Pathogenic to Humans") (Krzyściak et al., 2011).