Abstract: A method for extracting prion protein from a biological material, e.g., an animal tissue or product. In a specific example, abnormal prion protein is extracted from homogenized sheep brain with hexafluoro-2-propanol. The hexafluoro-2-propanol is separated from the aqueous brain preparation by increasing the ionic strength of the aqueous solution. Prion protein in the organic extract can be further purified, or the extract can be tested, e.g., by immunoassay, for the presence of prion protein, and more particularly abnormal prion protein. The extraction process permits testing for the presence of abnormal prior protein, e.g., for diagnosis of transmissible spongiform encephalopathies (TSE).