Stable isotope labeling with amino acids in cell culture (SILAC) relies on the in-vitro incorporation of stable isotopes into the cellular metabolism followed by Mass Spectrometry analysis in order to identify and quantify relative differential changes between 2 or 3 complex protein samples. Other labeling routes involve enzymatic labeling, for the incorporation of stable isotopes into the proteome at the peptide level, and chemical labeling when the samples cannot undergo metabolic labeling or in time-sensitive experiments.