The chapters in the two volumes ofBiomembrane Protocolsare broadly devoted to the methodologies involved in the structural and functional characterization of cell membranes. In many cases, a study of a particular membrane presupposes that it can be isolated by disruption of the cells and fractionation of the resulting homogenate, and then identified unambiguously. The early chapters of this volume,Biomembrane Protocols: I. Isolation and Analysis, are concerned with this fractionation process. Later chapters are concerned with the determination of composition, whereas in the second volume,Biomembrane Protocols: II. Architecture and Function, the methods associated with architecture and function predominate.