Aspergillus infection is often difficult to diagnose, and the usefulness of methods of culture for diagnosis has been questioned. We reviewed all respiratory cultures that yielded any species of Aspergillus and all surgical and autopsy materials suspected or diagnostic of infection with Aspergillus over a two-year period. Of 89 patients with one or more positive cultures of nonbiopsy respiratory tract specimens, eight had histologically proven disease (three had aspergillomas and five, invasive aspergillosis). All cases of disease were due to Aspergillus fumigatus or Aspergillus flavus, and eight of nine patients with two or more positive cultures of A. fumigatus or A. flavus had proven disease, versus one of 81 who were uninfected (P less than .001). Cultures from infected patients also had heavier growth and contained mixed Aspergillus species less often than did cultures from uninfected patients. We conclude that cultures of respiratory specimens are useful for diagnosis of pulmonary infection caused by Aspergillus.