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.

The Institute of Medicine and the National Research Council act under the 1863 congressional charter for the National Academy Sciences to advise the federal government. They also act on their own initiative to identify important scientific and health issues. The president of the Institute of Medicine is Dr. Kenneth Shine. The president of the National Research Council is Dr. Bruce Alberts.

Support for this project was provided by the U.S. Department of Health and Human Services (Contract Number NO1-OD-4-2139, TO 35). The views presented are those of the National Research Council and Institute of Medicine committees and are not necessarily those of the funding organization.

Library of Congress Catalog Card No. 98-83159