A wealth of experimental evidence argues that infectious prions are composed largely, if not entirely, of the scrapie isoform of the prion protein. We attempted to restore scrapie infectivity after exposure to protein denaturants including urea, chaotropic salts, and SDS. None of the procedures restored infectivity. Dialysis to remove slowly chaotropic ions and urea failed to restore scrapie infectivity. Attempts to create monomers of the scrapie isoform of the prion protein under nondenaturing conditions using a wide variety of detergents have been unsuccessful, to date, except for one report claiming that scrapie infectivity could be recovered from 12% polyacrylamide gels after SDS/PAGE [Brown, P., Liberski, P. P., Wolff, A. & Gajdusek, D. C. (1990) Proc. Natl. Acad. Sci. USA 87, 7240-7244]. We found that < 0.001% of the infectious prion titer could be recovered from the region of a polyacrylamide gel where the denatured proteinase K-resistant core of the scrapie isoform of the prion protein and other 30-kDa proteins migrate. We conclude that under the denaturing conditions used for SDS/PAGE, the scrapie isoform of the prion protein is denatured and little or no renaturation occurs upon injection of fractions eluted from gels into animals for bioassays.