Isotope dilution mass spectrometry (IDMS) is based on a simple and straightforward idea of using an isotope
labeled compound as an internal standard for quantitation purposes. IDMS now competes with routine quantitative methods
such as immunoassays (ELISA, RIA) due to its high precision, accuracy and robustness. The isotope dilution concept
allows for protein quantitation and has been showing great promise in clinical application in the last decade. The present
review contains a short description of the current status of proteomics and principles of absolute quantitative methodologies;
it focuses on some mass spectrometric techniques, sample preparation and recent examples of IDMS applications for
peptide and protein quantitation in clinical chemistry.