During a 4-week period, Aspergillus fumigatus caused disease in 2 patients and colonized a third patient in a renal transplant ward. Our investigation indicated that increased exposure of these patients to spores probably occurred during renovation of the ward one floor above it. Cases were significantly clustered (P = 0.014) during the period when work overhead caused dust to filter down through pores in the acoustical tiles of the false ceiling of the renal transplant ward. Swab cultures demonstrated A. fumigatus in the dust, and air samples showed heavy contamination with A. fumigatus and other fungi at and below a renovation site, but not on 2 distant wards. We concluded that dust can be an important source of aspergilli and that release of dust and spores during activities such as renovation may increase the risk of nosocomial Aspergillus infection in exposed, immunosuppressed patients.