There have been many important advances in our understanding of biological membrane structure and function over the last decade. Much of this progress has been driven by the development of new techniques for studying membrane components and their interactions. Tradition- ally, the investigation of membranes has largely occurred within the domains of biochemistry, physical chemistry, and cell biology; but many of the most significant advances have resulted from an expansion into other disciplines, such as molecular biology, immulogy, and the clinical sciences. In these two volumes we have attempted to bring together some of these techniques-to combine the old and the new. Biomembrane Protocols: II. Architecture and Function is concerned exclusively with the architecture and activities of membranes, whereas the companion volume, Biomembrane Protocols: I. Isolation and Analysis, deals with their isolation and compositional analysis. The aim of each chapter is to provide detailed technical and meth- odological information that will allow the reader to perform the tech- nique successfully, without the need to consult other texts. Detailed reviews of membrane structure and function are t included, except where they are relevant to the choice or efficacy of a particular proce- dure. In addition to Materials and Methods sections, each chapter has a Notes section that explains the reasons for taking certain steps and pro- vides practical tips for applying the techniques to other systems.