In recent years, advances in mass spectrometry have provided unprecedented knowledge of protein expression within cells. It has become apparent that many proteins function as macromolecular complexes. Structural genomics programs are determining the fold of these proteins at an increasing rate and electron microscopic tomography potentially provides a means to determine the location of these complexes within the cell. A complete understanding of the molecular mechanism of these proteins requires detailed information on the interactions and dynamics within the complex. Recent advances in mass spectrometry now make it possible to use hydrogen/deuterium exchange to detect intersubunit interfaces and dynamics within supramolecular complexes.