NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

Support for this project was provided by the U.S. Department of Defense (Contract No. DAMD17-02-C-0094). The views presented in this report are those of the Institute of Medicine Committee on Transmissible Spongiform Encephalopathies: Assessment of Relevant Science and are not necessarily those of the funding agencies.

For more information about the Institute of Medicine, visit the IOM home page at: www.iom.edu.

The serpent has been a symbol of long life, healing, and knowledge among almost all cultures and religions since the beginning of recorded history. The serpent adopted as a logotype by the Institute of Medicine is a relief carving from ancient Greece, now held by the Staatliche Museen in Berlin.

THE COVER: The cover photograph, provided by Dr. David Asher, is a histopathology slide of brain tissue from a patient with a prion disease. Stained with the chemicals eosin (red) and hemotoxylin (blue), the magnified tissue manifests microscopic holes (white circles). This report aims to guide scientists beyond histopathology toward new strategies to diagnose prion diseases non-invasively, rapidly, and early.