The conversion of the cellular isoform of the prion protein into the pathogenic isoform PrPSc is the key event in prion diseases. The disease can occur spontaneously genetically or by infection. In earlier studies we presented an in vitro conversion system which simulates the structural transition in recPrP by varying low concentrations of SDS at constant NaCl. In the present study we adopted the conversion system from experimental Scrapie in hamster to bovine recPrP and generated amyloid fibrils. The intermediate state which is optimal for fibril formation is a soluble, beta-rich state. The system was extended using BSE-prions as seeds and led to an acceleration of fibril formation by orders of magnitude. This seeded amyloid formation assay avoids any PK-treatment, is therefore able to detect even PK-sensitive PrPSc and does not require cellular components. (C) 2008 Elsevier Inc. All rights reserved.