The main reason for the difficulties in diagnosis of ABPA and ABPA exacerbations in CF patients is the overlap of diagnostic criteria for ABPA with common manifestations of CF. Pulmonary infiltrates, obstructive lung disease and bronchiectasis occur regularly in CF patients, due to the underlying disease with bacterial colonisation, and thus are not specific to ABPA. Furthermore lung colonisation with A. fumigatus occurs in 20-25% of CF patients. Therefore, as stated in the most recent consensus document on diagnosis and therapy of ABPA in CF patients, serological findings should contribute strongly to the confirmation or exclusion of clinically suspected ABPA (Stevens, Moss et al. 2003).