Intravenous administration of stable isotope labeled amino acid ((13)C6-leucine) to humans recently made it possible to study the metabolism of specific biomarkers in plasma using High Resolution mass spectrometry (MS). This labeling approach could be of great interest for monitoring many leucine-containing peptides in parallel, using HRMS. This will make it possible to quantify the rates of synthesis and clearance of a large range of proteins in humans with a view to obtaining new insights into protein metabolism processes and the pathophysiology of diseases such as Alzheimer's disease.