In recent years novel molecular methods, notably polymerase chain reaction (PCR) assays, have been developed to improve the diagnosis of life-threatening invasive aspergillosis in patients at high risk, especially patients with malignant hematological disease. Early diagnosis and treatment are essential for adequate therapeutic management. Management, however, often remains difficult since most of the diagnostic tools used clinically at present either lack specificity or acceptable sensitivity. The clinical value, advantages and remaining problems of PCR approaches to detect the emerging fungal pathogen are reviewed.