The diagnosis of invasive aspergillosis may be hard to establish. One of the problems in diagnosing invasive pulmonary aspergillosis is that the isolation of Aspergillus from respiratory secretions or its presence on a Gram stain preparation may be misleading, because the fungus can be a colonizing organism or the result of laboratory contamination as well. The diagnosis of invasive aspergillosis requires the demonstration of the fungus in tissue specimens. Also, Aspergillus infection should be confirmed by culture, since it cannot be diagnosed with certainty by microscopy. Other fungi such as Pseudallescheria boydii and Fusarium appear identical in histopathologic sections. This distinction is important, because these fungi are less responsive to amphotericin B therapy, which is the drug of choice for the treatment of Aspergillus infection. In the case presented, no pathogen could be identified from the sputum or BAL fluid. Culturing Aspergillus from sputum is difficult, with positive results in only 8 to 34% of cases. BAL is an important tool in investigating pulmonary infiltrates in a bone marrow transplant recipient, with a diagnostic yield (all causes) of 50 to 75%. In patients with pulmonary aspergillosis, bronchial washings and BAL are safer, with a higher sensitivity than transbronchial biopsy. The specificity of BAL is lower than that of transbronchial biopsy but is still acceptable if the patient is considered to be at a high risk for opportunistic infections and if the organisms can be seen by staining or culture. For the diagnosis of invasive pulmonary aspergillosis, we depend largely on invasive procedures. However, immunocompromised patients often are extremely ill and have thrombocytopenia or other contraindications to biopsy. Therefore, it is mandatory to use serologic and DNA detection assays for the diagnosis of invasive aspergillosis. One currently promising noninvasive tool in diagnosing invasive aspergillosis is the serial screening for circulating galactomannan, a major aspergillar cell-wall constituent, which is released during invasive disease. Maertens et al conducted a prospective study that analyzed the diagnostic contribution and accuracy of the galactomannan test (an enzyme-linked immunosorbent assay) for diagnosing invasive aspergillosis in 191 prolonged neutropenic patients and stem cell recipients. Although serial sampling was necessary to maximize detection, they could demonstrate the presence of antigenemia in all patients with proven invasive aspergillosis. The test proved to have a sensitivity of 89.7% and a specificity of 98.1%. The positive and negative predictive values equaled 87.5% and 98.4%, respectively. Therefore, we think that the galactomannan test is useful for clinical decision making. A confirmed positive test result (especially rising titers) in a relevant clinical setting should encourage clinicians to start (or change to) antifungal therapy. However, it should be kept in mind that the species specificity of the assay cannot exclude the involvement of other fungal pathogens with a similar clinical presentation (eg, Fusarium, Alternaria, and Mucorales) and does not provide information about coinfections (eg, Cytomegalovirus and Candida). In conclusion, we believe that galactomannan detection provides supportive evidence of the Aspergillus etiology of an infectious process in the right context. It does not replace other diagnostic tools in the workup of unexplained fevers and in the exploration of invasive fungal infections in general in high-risk hematology patients.