Background: Invasive aspergillosis (IA)) is a serious cause of morbidity and mortality in immunocompromised patients with haematologic malignancy. The serum galactomannan enzyme immunoassay (GM-EIA; Platelia Aspergillus EIA; Bio-Rad) was cleared by the Food and Drug Administration at an optical density index cut-off of 0.5 for a probable diagnosis of invasive aspergillosis. In this prospective study GM-EIA (Platelia Aspergillus EIA, Bio-Rad) with 0.5cut-off value and sequential sensitivity-specificity for single, consecutive two and consecutive three positivity were investigated for the diagnosis of IA in neutropenic hematologic patients. Methods: Serum samples were taken twice a week from patients during their hospitalization. IA was classified according to European Organisation for Research and Treatment of Cancer and Mycoses Study Group Guidelines as “proven”, “probable”, and “possible”. The sensitivity was calculated from the results of patients with proven/propable and the specificity was calculated from the results of patients non-IPA patients. Results: In 165 consecutive febrile episodes in 106 patients, 80 (48.5%) episodes were defined with IA (4 proven, 11 probable, 65 possible) and 85 (51.5%) episodes were defined as non-IA. Per episode average 8.3 serum samples were examined for a total of 1385 serum samples. Cut-off value of single GM-EIA = 0.5 for proven/probable IA with sensitivity/specificity 100%/ 27%, two consecutive positive GM-EIA = 0.5 with sensitivity/specificity 86%/ 71% and three consecutive positive GM-EIA = 0.5 with sensitivity/specificity 73%/85% were obtained. Conclusions: Measuring the level of galactomannan twice a week and consecutive monitoring reduced the sensitivity and increased the specificity. Monitoring of the GM-EIA frequently from the first positivity can increase sensitivity/specificity.