This proposal requests funding to replace two ESR spectrometers in a major, highly productive Chemistry Department. The investigator proposes to purchase a sensitive, state-of-the-art x-brand spectrometer with high speed, versatile data handling capabilities that will benefit the research programs supported by this instrument encompass spin label studies of enzymes and proteins of the coagulation pathway, in-vivo ESR, the chemistry of photo-induced carbene and photo-affinity labeling chemistry in enzymes and nucleic acids, structural characterization of heme protein models and spin label studies of ribosomal RNA's.