The diagnosis of invasive fungal infections--in particular those caused by Candida and Aspergillus--is difficult and often delayed. The conventional laboratory diagnosis relies on direct microscopic examination and culture of relevant clinical material, as well as on histology. To improve and speed up the microbiological diagnosis, two new approaches have been thought, the detection of circulating cell wall fungal antigens (galactomannane from Aspergillus, mannane from Candida, glucane), and the detection of fungal specific nucleic acids by PCR directly in clinical materials. Among these still experimental methods, the serial detection of galactomannane in the serum of at risk patients is now considered as a useful adjunct for the early diagnosis of invasive aspergillosis.