The International Life Sciences Institute (ILSI) was creat ed to promote cooperative efforts toward solving critical health and safety questions involving foods, drugs, cosmet ics, chemicals, and other aspects of the environment. The Officers and Trustees believe that questions regarding health and safety are best resolved when government and industry rely on scientific investigations, analyses, and reviews by independent experts. Further, the scientific aspects of an issue should be examined and discussed on an international basis, separate from the political concerns of individual companies. ILSI is pleased to sponsor this set of monographs on the pathology of laboratory animals. This project will be use ful in improving the scientific basis for the application of pathologic techniques to health and safety evaluation of substances in our environment. The world wide distribu tion of the authors, editors, and Editorial Board who are creating these monographs strengthens the expectation that international communication and cooperation will al so be strengthened.