Air sampling of the rooms and corridors of the oncology wards of the hospital was carried out over a 54-week period to assess the concentration of viable Aspergillus conidia. A. fumigatus and A. flavus were recovered at a mean of 1.83 cfu m-3 air sampled. Individual samplings yielded concentrations of up to 11.6 cfu m-3. Other Aspergillus spp. were recovered at a mean of 2.38 cfu m-3 (maximum 32.6 cfu m-3). Concentration was not correlated with season or hospital ward. Review of autopsy results showed an average of 6.6 cases of aspergillosis annually over a 22-year period. No seasonal variation in case incidence was found. Six cases of invasive aspergillosis were diagnosed on the three cancer wards during the air-sampling period, but no association was seen linking these cases with changes in recovery of airborne Aspergillus. A seasonal pattern was not observed in the overall incidence of aspergillosis cases nor concentrations of airborne conidia.