Although many prophylactic measures have been attempted, Aspergillus continues to be a significant cause of morbidity and mortality in neutropenic BMT patients. The data describing the efficacy of AAB in patients with neutropenia is ambiguous and inconclusive. All of the available studies lack adequate study design, making a definitive conclusion difficult. Additionally, the role of concomitant oral antifungal prophylaxis has not been addressed and needs to be examined. Regardless, the studies suggest AAB may be effective during periods of environmental exposure to Aspergillus, as seen during periods of construction, when used in combination with HEPA filtration. Further investigation is required to assess the effectiveness of AAB in BMT patients who are not housed in sterile environments. Until more information is available, the role of AAB in preventing IPA in neutropenic BMT patients remains unclear, particularly in the absence of HEPA filtration.