More than ever, the introduction of new methods or techniques serves to stimulate progress into understanding the structure and function of the nervous system. This axiom is exemplified by recent techniques that have revolutionized several branches of neurochemistry and promise to remain dominant for many years. Such developments underscore the need to remain abreast of new research strategies and provide further justification for the present series. The use of high performance liquid chromatography combined with bioassay methods provides a powerful technique for iso­ lation and assay of trace amounts of neuropeptides. Two chapters in the present volume deal with this subject: one (Stenn and Lewis) describes the assay of enkephalins, and the other (Chretien and Seidah), on lipo­ tropic peptides, includes procedures for structural analysis by microse­ quencing. These methods rival earlier ones for peptide separations in speed, sensitivity, and cost and have general applicability in most labo­ ratories. High performance liquid chromatography has also largely sup­ planted earlier and more tedious procedures for the assay of catechola­ mines, as described in Chapter 7 by Causon. As in earlier volumes, we have striven to retain a balance between studies on intact tissues and those on subcellular components.