This is a proposal requesting funds to purchase a state-of-the-art high resolution mass spectrometer for shared use by seven major NIH-supported users at two campuses of the University of California. These scientists, at the University of California, Riverside and University of California, San Diego do not presently have such instrumentation available to them. The requested instrument will be installed at the University of California, Riverside and operated under the supervision of the principal investigator, with the advice of an intracampus advisory board, to provide much needed high resolution mass spectrometry service to this user group on a timely basis.