The International Life Sciences Institute (ILSI) was estab lished to stimulate and support scientific research and edu cational programs in nutrition, toxicology, and food safe ty; and to encourage cooperation in these programs among scientists from universities, industry, and government in order to facilitate the resolution of health and safety issues. The officers and trustees of ILSI believe that questions re garding health and safety are best resolved when govern ment and industry rely on scientific investigations, analy ses, and reviews by independent experts. This process is furthered by the examination and discussion of issues on an international basis. ILSI is pleased to sponsor this set of monographs on the pathology of laboratory animals. This project collectively brings together the most comprehensive information on non-neoplastic and neoplastic lesions that occur in com monly used laboratory animals. The international compo sition of the authors, editors, and editorial board who have contributed to these monographs strengthens our expecta tions that understanding and cooperation will be strength ened worldwide through this series.