Aspergillosis is a serious and often fatal infection in the bone marrow or organ transplant patient, for which improved methods of diagnosis are desperately needed. Currently, the diagnosis is most often made based on clinical findings and radiographic findings, which are nonspecific, and toxic therapies are initiated empirically, often without ever establishing the diagnosis. Without a definitive diagnosis, physicians often withhold or reduce the doses of the antifungal agent when toxicity develops or the patient improves, permitting progression of disease in those with invasive aspergillosis. The Platelia Aspergillus galactomannan antigenemia assay may assist physicians in making these decisions. With a sensitivity of 81% and a specificity of 89% in the studies leading to its FDA clearance, physicians still must be aware of the potential for false-positive and false-negative results; the test does not replace careful microbiological and clinical evaluation. This report will review the relevant literature and provide guidelines for use of the test in patient management.