Abstract: A method of concentrating a disease-related conformation of a protein such as the PrP.sup.Sc in a sample is disclosed. The method comprises liquefying the sample and adding a complexing agent such as phosphotungstic acid (PTA) which complexes preferentially or exclusively with the PrP.sup.Sc. After the complex is formed the composition is centrifuged until the complex settles at the bottom. Thereafter, the supernatant is poured away. The remaining pellet may be resuspended in an aqueous solution containing a protease inhibitor for storage. The PTA stains the PrP.sup.Sc making the resulting concentrated PrP.sup.Sc susceptible to further analysis, making it possible to quickly and efficiently determine the presence of PrP.sup.Sc and its concentration in a sample. The method can be used to render a sample non-infectious by removing all or substantial of the infectious form of a protein from a sample.