Harry Baker and Rosalind Ridley have done an admirable job in assem bling this collection of articles that describe the methodology frequently used to study a group of CNS illnesses often referred to as the "prion diseases." Research on prions and the disorders that they cause has progressed relatively rapidly over the last decade since the discovery of the prion protein (PrP) that allowed the application of modem molecular biological and genetic tools. The power of these techniques is awesome and their use in deciphering the once mysterious prion diseases has brought a wealth of new information. Although prions are unprecedented pathogens, appearing to consist only of PrPSc molecules, the diseases that they cause are no less remarkable. The prion diseases in animals include scrapie of sheep and goats as well as "mad cow" disease or bovine spongiform encephalopathy (BSE). In the United King dom, the epidemic of BSE has heightened public awareness of this previously obscure group of diseases such that any work in the field is likely to stir up interest in the media and become a subject of public debate. It has been diffi cult for British investigators to work on prion diseases without being involved in these controversies. As such, several chapters have been included that deal with political and social issues surrounding prion diseases. The human prion diseases present an equally fascinating saga in which these CNS degenerations present as genetic, sporadic, and infectious illnesses.