ment with the drug. The author concluded that the A. fumigatus strains acquired resistance to itraconazole during or following treatment. The author, however, failed to determine whether or not the isolates cultured from the sputa were genotypically identical. Although invasive infections by Aspergillus species are generally caused by a single genotype (2), isolates cultured from non-sterile sites such as sputum may be genotypically unrelated to the pathogenic strain. A. fumigatus is ubiquitous in the environment and the genetic diversity is enormous (3). Therefore, an isolate cultured from sputum could be a contaminant or just a colonizing strain. Genetic variation among A. fumigatus isolates cultured from sputum has been shown for patients with aspergilloma (4‐6) and for those with cystic fibrosis (7). In patients with aspergilloma, usually 1 predominant genotype is found, but several types may be present. We have previously genotyped 23 A. fumigatus isolates from two patients with cystic fibrosis by random arbitrary polymorphic DNA (RAPD)-PCR and by restriction fragment length polymorphism (RFLP) (7). The isolates were collected over a period of 2 y. In one patient, 3 genotypes