We calculated an elastase activity index (EAI) by dividing the diameter of the elastin lysis halo by the fungal growth diameter. After 10 days' incubation at 37 degrees C, all strains but one obtained from invasive aspergillosis showed an EAI > or = 1. Of the 18 strains obtained from colonized patients, only 4 (22.2%) had an EAI > or = 1, whereas neither of the strains isolated from patients with fungus ball reached this value. Overall, 44 out of the 142 strains obtained from the environment had an EAI > or = 1 (30.9%).