Fungi of the genus Aspergillus are moulds with low nutrient requirements, that are ubiquitous in our environment. My bachelor thesis deals with the quantitative detection of Aspergillus spp. out of organ-homogenates from mice. Moreover, we detected and identified those fungi in human blood serum. In general, this project is a method establishment in basic research, having an important diagnostic character. At first, the mice organs had to be homogenized. In addition to that, the best suitable method for DNA extraction (DNA = Deoxyribonucleic acid) had to be chosen. Due to promising results, the UltraSens Virus Kit (QIAGEN) was kit of choice for DNA isolation. Before the nucleic acid is extracted, a ‚bead beating‘ cell disruption method had to be conducted. It turned out, that the use of glass beads resulted in a better homogenation and DNA availability than sand-filled tubes (FastPrep-24, MPBIO). Concerning the quantitative PCR (= polymerase chain reaction; BIORAD-PCR), it is important to mention that different dilutions must be used for different organs, to avoid mice-DNA inhibition of PCR reaction. Finally, the construction of calibration series has been conducted. In addition to that, it should be noticed that concerning mouse brain and mouse spleen, it was possible to carry out a first graphic representation of the received research results.