In the early eighties when the H3 receptor was identified, many thought that an H3 ligand, an agonist or an antagonist, would become available as a therapeutic agent. This has not occurred. The reason for this could be the fact that many investigators consider histamine mainly, if not only, as a mediator present in for example mast cells being released during allergic events. However, it has become apparent that histamine is an important neurotransmitter. Its role in the nervous system, especially in the central part of it, is rather extensive.

The H3 receptor is mainly found as a presynaptic one, both on histaminergic neurons (the auto-type) and on other neuronal systems (the hetero-type). Both the H3 agonist and the H3 antagonist cause important pharmacological effects. Several ligands have become available now, including radiolabelled analogues.

In this book, the current state of affairs with regards to the medicinal chemistry and pharmacology of the H3 receptor and the several ligands available are presented by a number of experts in the field. The book presents an extended review of what has happened since the first H3 paper appeared. The editors hope that publication of this work will lead to an increase in interest of both academia and industry for the H3 receptor, especially as a target for drug development.

Volume 45 of "Progress in Drug Research" contains eight reviews and the various indexes which facilitate its use and establish the connection with the previous volumes. The articles in this volume deal with neuro peptides as native immune modulators, with Calmodulin and with effects of cell stimuli and drugs on cellular activation, with recent advances in benzodiazepine receptor binding studies, with the medicinal chemistry and therapeutic potentials of ligands of the histamine H3 receptor, with Serotonin uptake inhibitors, with computer-aided drug design, with natri uretic hormones and with the recent developments in the chemotherapy of osteoporosis. In the 36 years that PDR has existed, the Editor has enjoyed the valu able help and advice of many colleagues. Readers, the authors of the reviews and, last but not least, the reviewers have all contributed greatly to the success of this series. Although the comments received so far have generally been favorable, it is nevertheless necessary to analyze and to reassess the current position and the future direction of such a series of monographs. So far, it has been the Editor's intention to help disseminate information on the vast domain of drug research, and to provide the reader with a tool with which to keep abreast of the latest developments and trends. The reviews in PDR are useful to the nonspecialist, who can obtain an overview of a particular field of drug research in a relatively short time."