This proposal requests funds to establish a Center for Frequency and Time Domain Fluorescence Spectroscopy at the University of Maryland, School of Medicine. The primary research instrument of the center will be a frequency-domain instrument for fluorescence spectroscopy and state-of-the-art time-correlated photon counting. Initially the center will function as a shared-use facility for four scientists but will evolve into a regional resource. The new frequency domain instrument will be only the second of its kind and the first to be made available to other users. Dr. Lakowicz, the principal investigator, is a leader in the development of phase methods and has demonstrated his ability to get results from complex state-of-the-art instrumentation. Support is recommended.