The Stable Isotope and Metabolomics Core can provide targeted and untargeted metabolite profiling of plasma or tissue, and the rate of change of substrates (flux), using stable isotopes and mass spectrometry. The core has a variety of in vitro and in vivo metabolic methodologies that can determine substrate flux dynamics and metabolite profiles at the organelle, cellular, tissue and whole body levels. In collaboration with other Diabetes Research Center cores, the application of mass spectrometric and other methodologies allows the elucidation of metabolic mechanisms underlying disorders in fuel homeostasis. The metabolic role of candidate molecules can be specifically delineated in vivo and in vitro, using a step-by-step hypothesis-driven approach in animals, cell lines and other models.