This book is the compilation of papers presented at the International Symposium on in vivo Body Composition Studies, held at the University of Toronto, Ontario, Canada, June 20 - 23, 1989. The purpose of this conference was to report on advances in techniques for the in vivo measurement of body composition and to present recent data on normal body composition and changes during disease. This conference was the most recent of several meetings on body composition studies, and follows two successful such meetings, one at Brookhaven National Laboratory in 1986, and at Edinburgh in 1988. The large number of excellent research papers and posters presented at these conferences demonstrates the rapid growth of the field and the broad interest in the subject of in vivo body composition studies. The proceedings of the Brookhaven meeting "In Vivo Body Composition Studies", is published by The Institute of Physical Sciences in Medicine, London. Both the Brookhaven and the current Toronto meeting emphasized the clinical applications, together with the techniques employed. The Edinburgh meeting placed more emphasis on the methodological problems and design of instrumentation. Because of the number of papers presented at the meeting it was necessary to ask the authors from the same institution to combine their presentations into a single paper where appropriate. The editors wish to thank the authors for their cooperation and for graciously accepting the minor revisions made to each manuscript.