The molecular composition of the blood provides information regarding one’s state of health, and may be compared to an individual fingerprint. In principle, changes in the constituents of blood can serve as early signs of disease. However, before chemical fingerprints can be utilized for diagnostic purposes, the stability of the molecular patterns in healthy persons over time must be firmly established. Researchers under the direction of Dr. Mihaela Žigman, Head of the Broadband Infrared Diagnostics (BIRD) group in the Department of Laser Physics led by Prof. Ferenc Krausz at LMU Munich and the Max Planck Institute of Quantum Optics (MPQ), in collaboration with Prof. Dr. Nadia Harbeck at the LMU Medical Center, have now successfully accomplished this task. With the aid of a method known as Fourier-transform infrared spectroscopy (FTIR), the team has shown that the molecular composition of blood samples obtained from a cohort of healthy donors remains stable over a period of several months, and confirmed that each of the resulting spectra could be clearly assigned to an individual person.