Mass spectrometry-based quantitative proteomics strategies are ideally adapted to the detection of global protein changes between different biological samples. Among these, SILAC (stable isotope labelling by amino acids in cell culture) has demonstrated a great potential. This method is extremely accurate and relatively easy to apply for the quantification of proteins extracted from cultured cells. SILAC involves cell culture either in regular culture media ("light" protein synthesis) or in media where amino acids have been replaced by their isotopically labelled counterparts ("heavy" protein synthesis). Cell populations to be compared can be mixed and treated as a single sample, which allows downstream sample preparation without the risk of introducing quantification errors. During mass spectrometry analysis, the relative protein abundance between biological samples can be calculated from the intensities of heavy and light peptides. As shown by numerous applications in biological and clinical studies, SILAC represents a promising method for the elucidation of cellular and physio-pathological mechanisms and for the identification of disease biomarkers. The restriction of SILAC to the quantification of proteins from cultured cells has just been overcome with the description in a recent paper of a SILAC mouse, which will allow this technology to be applied to the differential study of -tissues and biological fluids from model animals.