The present volume contains all the papers presented at the International Conference on Membrane-Bound Enzymes held at Pavia in May 1910. The publication of its scientific content has been made possible by the collaboration of many scientists who have taken part at the Symposium and who deeply and actively discussed the lectures which were delivered. In order to ensure rapid pu blication, however, the discussion will not be reported here. The general subject of membrane-bound enzymic activity, its behavior, localization and regulation, was explored in depth from the standpoints of the various contributors in biophysics, bioche mistry, cytology and pharmacology. Each session was briefly in troduced by the session chairman's remarks about the field under discussion. At the end of the Conference, Dr.R.M.C.Dawson made some concluding remarks. The meeting is considered to have been very successful. It certainly gave a further stimulus to biochemical and physiological research workers in this field of study. The editors express their thanks to the authors of the papers and to the Plenum Publishing Corporation for the prompt response which has enabled the rapid publication of the volume, and to the auditorium of the meeting, which was attended by more than one hundred research workers con cerned with the problems of membrane biology. We are happy to acknowledge the financial support of various organizations, which have been listed in another part of this book.