Invasive aspergillosis is one of the most frequent fungal infections in neutropenic patients, in whom it is associated with a high mortality. Its diagnosis is difficult by the traditionally used laboratory tests. In the last years, an ELISA (Platelia Aspergillus, Bio-Rad, France) to detect galactomannan in neutropenic and cancer patients with high risk of suffering invasive aspergillosis has been developed. The experience accumulated in Spain in the diagnosis of invasive aspergillosis by Platelia Aspergillus is presented in this monograph.