In order to maintain fair play in sports and to guarantee the health of the athletes, doping tests are carried out on blood and urine samples. Pharmaceutical companies develop and introduce new (therapeutic) substances on a regular basis. Some of these newly developed compounds can be used by athletes to gain a competitive advantage. To combat this abuse, doping control laboratories must develop analytical methods to detect these substances in blood and urine. This project aims to investigate the traceability of doping agents in urine and blood using liquid chromatography coupled to mass spectrometry (LC-MS). Since pharmaceutical biotechnology has made great progress in the last 20 years, many (recombinant) peptide-based therapeutic substances have been introduced including insulins, growth hormone and insulin like growth factor (IGF-I) and many more. Therefore, this project will mainly focus on the detectability of peptide doping agents.