During scrapie infection an abnormal isoform of the prion protein (PrP), designated PrP^sc, accumulates and is found to copurify with infectivity; to date, no nucleic acid has been found which is scrapie‐sepecific. Both uninfected and scrapie‐infected cells synthesize a Prp isoform, denoted PrP^c, which exhibits physical properties that differntiate it from PrP^sc was purified by immunoaffinity chromatography using a PrP‐ sepecific monoclonal antibody cross‐linked to protein‐A‐Avidgel. PrP^sc was purified by detergent extraction, poly(ethylene glycol) precipation and repeated differentila centrifugation of PrP^sc polymers. Both PrP isoforms were found to have the same N‐terminal amino acid sequence which begins at a predicted signal peptide cleavage site. The first 8 residues of PrP^c found to be KKXPKPGG and the first 29 residues of PrP^c were found to be KKXPKPGGWNTGGSXYPGQGSPGGNRYPP. Arg residue 3 and 15 in PrP^sc and 3 PrP^c appear to be modified since no contain an intramolecular disulfide bond, liking Cys 179 and 214, which creates a loop of 36 amino acid containing the two N‐ linked glycosylation sites. Developement of purification of how PrP^sc is synthesized either form PrP^c or a precursor.