The diagnosis of invasive Aspergillosis (IA) remains a challenge in the febrile neutropenic and the hematopoietic stem cell transplant (HSCT) recipients. Recent studies have shown that early diagnosis of IA is possible in this group of high-risk patients. Serial screening of circulating Galactomannan (GM), an epitopic determinant of several antigens secreted by the Aspergillus early in its growth, has been shown to be sensitive and specific in the diagnosis of IA. This test may help us to detect IA early, thereby permitting a pre-emptive strategy to be initiated in high-risk patients. In a prospective, randomized, non-blinded study, we seek to compare the outcome of a novel GM-guided anti-fungal strategy against the conventional empirical antifungal therapy. Patients randomized to the conventional arm will not undergo serial GM monitoring, but will receive standard anti-fungal prophylaxis and standard empirical antifungal therapy in accordance with published guidelines. Patients randomized to the GM arm will receive standard anti-fungal prophylaxis but will not receive empiric anti-fungal therapy unless 2 GM readings are positive. The study aims to determine if such a strategy permits targeted, pre-emptive therapy in those at greatest risk, and spare febrile patients without evidence of fungal infection other than prolonged fever from unnecessary and potentially toxic therapy. It also aims to determine if GM guided pre-emptive antifungal therapy using Amphotericin-B deoxycholate prevents the development of proven or probable invasive aspergillosis (IA). The study will also prospectively evaluate (in a blinded fashion) the use of realtime polymerase chain reaction (RT PCR) assay in the same cohort of patients receiving GM serial monitoring, and investigate its role in the diagnosis and treatment monitoring of invasive Aspergillosis.