The International Symposium on Heparin, held May 13-15, 1974, in St. Louis, Missouri, as a part of the dedication of the Shoenberg Pavilion of the Jewish Hospital of St. Louis, was conceived as a forum to bring together physicians and scientists with a basic in terest in the structure, function and clinical usefulness of heparin. Few naturally occurring substances have commanded the breadth of interest among members of the biomedical research community as this compound has. Aspects of its covalent and three-dimensional struc ture, its biosynthesis, its interaction with and effect on physio logically important moieties and its use as a therapeutic agent in a variety of disease states have been actively studied for the past several decades. Thus, the present state of these studies seemed to be a timely subject for discussion, not only to gather together in one place representative samples of the myriad of data on heparin but also to underscore the ever increasing necessity for communica tion between basic research and clinical practice."

The NATO Advanced Study Institute entitled "Surface Membrane Receptors: Interface Between Cells and Environment" was held in Bellagio, Italy September 13-21, 1975. This meeting was an attempt to bring together in an international and interdisci plinary forum scientists who are studying recognitive phenomona which take place at the surface membrane of cells. While an attempt was made to restrict the subject areas covered at the meeting to those experimental systems which have been biochemi cally characterized to some extent, it will also be noted that some contributions to this volume represent a preliminary iden tification of interesting regulatory substances which might reasonably be expected to act at the cell surface. This book is divided into four sections reflecting the subject areas covered during the course of the meeting. The first section entitled "Membrane Structure and Receptor Function" is intended as an overview of the role of membrane structure in determining the regulatory properties, physical state, structure and location of cell surface receptors. It should be noted that the plasma membrane itself provided the unifying theme for the intention ally diverse contributions to this volume. The following three sections represent an arbitrary division into three levels of structural complexity of the things in their external environ ment with which cells must specifically interact.