Preparations of in vivo labelled RNA from normal and scrapie infected mouse brains were fractionated by polyacrylamide gel electrophoresis. No appreciable differences were detected between the two preparations. The biological activity of preparations of RNA and DNA from scrapie brain was also examined. In each case the nucleic acid was obtained by one method envolving the use of phenol and one without phenol. Attempts were made to bind the nucleic acid to normal membrane by three different methods. In no instance was a single case of scrapie obtained by inoculating nucleic acid extracts from scrapie brain either alone or associated with normal membranes. It is concluded that a putative scrapie-specific nucleic acid must either be present in scrapie brain in such an unusual from that it is not extracted readily by methods suitable for the preparation of most virus nucleic acids; or, if it is extracted, that it has no detectable biological activity. In either case, the scrapie agent differs substantially in its properties from the plant viroids.