In recent years, we have witnessed a rapid expansion of our knowledge regarding the role of the endothelium in the control of vascular tone (and organ perfusion) in health and disease. Physiology, pharmacology, and molecular biology have uncovered a wealth of information on structure and function of this heretofore largely neglected "organ". Clinical medicine is now called upon to define the clinical significance of these observa tions that imply the mechanisms of blood coagulation, e.g., the interaction of throm bocytes with the endothelium, vasomotor control, and specifically, the regulation of smooth muscle tone with consequences for vascular resistance and conductance and organ blood flow. Finally, metabolism of lipids with the everlasting problem of athero sclerosis is an important aspect. In a second step, implications regarding the improvement of current therapeutic con cepts, as well as the development of new modalities of pharmacotherapy will have to be discussed. The topic addressed by the 1990 Gargellen Conference: Endothelial Mechanisms of Vasomotor Control, clearly is of interest for both basic scientists and clinicians. It has been the aim of the organizers, the Society for Cooperation in Medical Science (SCMS) with this and the previous symposia to foster and support both basic science and clinical research. Research in medicine today shows two major directions of development: on the one hand, increasing involvement of the basic sciences and their methodology. On the other hand, statistical validation of concepts and therapeutic strategies in large scale population-and multicenter-studies.