2005 Annual Report 4d.Progress report. This report serves to document research conducted under a specific cooperative agreement between ARS and the University of Santiago De Compostela, Santiago, Spain. Additional details of research can be found in the report for the parent CRIS 5325-32000-003-00D, Development of New Technologies for Detection of Prions in Animal Feed and Environmental Samples. This is the first year for this Project. The goal of the proposed research is to develop molecular methods, based on mass spectrometry, to distinguish and thereby analyze different prion strains. Specifically, we are using tandem mass spectrometry to identify and quantitate peptides of different molecular weights after treatment of the proteinase K resistant core prion molecule with trypsin. Our method will be useful to determine whether North American BSE is the same as United Kingdom BSE or more analogous to atypical BSE. The UK strain has been linked to feed contaminated with BSE, whereas the atypical cases are hypothesized to be of sporadic origin. Our work is proceeding apace. It has already resulted in filing of a Provisional US Patent Application.