This volume represents the proceedings ofthe invited lectures ofthe first International Symposium on Serotonin from Cell Biology to Pharmacology and Therapeutics which was held in Florence on March 29 -Aprill, 1989. This meeting, held under the co-sponsorship of the Serotonin Club and the Fondazione Giovanni Lorenzini, represents the first attempt to bring together scientists fascinated by the complexity of the action of 5-hydroxytryptamine throughout the body and in various species. Hence this volume provides the reader with the unique overview of the sources, effects, receptors, physiological actions and pathological role of Serotonin. As such it will be of interest not only to the person devoting herorhis research efforts to the study of 5-hydroxytryptamine but also to all scholars and even clinicians wanting to know how the powerful monoamine can modulate cellular functions. To accelerate the publication of these proceedings the Editors and the publishers have selected the camera ready format and have avoided a lengthy refereeing process. Hence the scientific content of, and the opinions expressed in the chapters are the sole responsibility of the authors. The Editors Milan and Houston The Editors want to thank Mrs. H. Liepman and her staff at Kluwer for the prompt and efficient handling of the manuscripts.