Forty three isolates of Aspergillus terreus of environmental or clinical origin were typed by random amplification of polymorphic DNA (RAPD) with two different primers NS3 and NS7 from the fungal ribosomal 18S subunit gene. For the 31 epidemiologically unrelated isolates tested, the primers NS3 and NS7 gave rise to 23 and 24 different genotypes, respectively, and combining the results obtained with the two primers allowed the differentiation of all these isolates. No clustering was found in relation to pathogenicity, clinical signs, or geographic origin of the isolates. Five groups of related isolates of A. terreus were also typed. Analysis of sequential isolates from patients with cystic fibrosis or with invasive aspergillosis showed the clonality of the colonization or infection by A. terreus. Likewise, this straightforward typing method demonstrated the clonal origin of a massive contamination of the environment in a haematology unit. Therefore this RAPD typing method may constitute a valuable tool for the epidemiological follow-up of airway colonization in patients with cystic fibrosis or investigations of links between nosocomial outbreaks of invasive aspergillosis and environmental contamination