Measuring dynamics of proteins abundance in cells in response to stimuli such as growth factors or drugs requires analysis of more than one time point. Proteomic approaches have traditionally been used to measure only one state at a time because quantitation is difficult, especially when mass spectrometry is used as a readout. Isotopically labeled reagents have recently been introduced that allow comparison of two or three different states by mass spectrometry. Here, we evaluate the reproducibility of an experiment that measures three states simultaneously through stable isotope labeling of cells with amino acids in cell culture (SILAC) using light, medium, and heavy versions of amino acids. The major goal of this study was to assess the reproducibility of such experiments in combination with liquid chromatography tandem mass spectrometry (LC-MS/MS). Our results show that it is possible to obtain reproducible quantitative data to study protein dynamics based on our analysis of more than 220 peptide sets derived from 20 proteins from 3 different LC-MS/MS runs.