Recent experimental and clinical research performed by outstanding authorities has enabled us to characterize fundamental processes that govern the regulation of salt and water content of the body. Their results have provided not only an important gain of insight into mechanisms at the cellular level but also the possibility to integrate single cell activities into a complex organ function. Moreover, this knowledge enables scientists to develop broader concepts concerning the regulation of organ function and thus contributes to a better understanding of the overall status in health and disease. In the present volume some of these physiologists and clinicians discuss principal questions of humoral and non-humoral influences involved in the control of electro­ lyte and fluid content of the organism. It contains three essential topics: Data concerning basic principles of cell behaviour and transport processes are followed by the description of natriuretic substances and their influence on volume regulation. Finally, attempts are undertaken to elucidate the meaning of these basic principles for the explanation of the development of patholocigal states. This symposion was held in honor to Professor H. P. Wolff, one of the internatio­ nally wellknown pioneers in this field of clinical research. The editors· wish to express their graditude to the Melusin-Schwarz-Monheim GmbH for the generous support of the symposion.