The papers collected in this volume were presented at the International Symposium on Hypotensive Peptides held in Flor ence, Italy, on October 25-29, 1965. The purpose of the meeting was to bring together scientists of fourteen countries ranging from the chemist to the surgeon, who usually do not speak a common language and for whom it would be quite difficult to follow the latest developments in fields allied to, but still some what removed from their basic interest. Their reports sum marized their recent progress and current achievements, and gave indication of the trend that future research on hypotensive peptides may take. Various aspects of the structure and function of brady kinin, kallidin, kallikrein, gastrin, eledoiSin, physalaemin, sub stance P, and related substances were discussed during the nine sessions. The first session was devoted to the chemistry of peptides. This was followed in loose order by reports dealing with the structure of some newer peptides, with kininogen, and with enzymes that release or inactivate peptides. Subsequently, reports on the physiological, pharmacological, pathological, and clinical importance of kinins, kallikrein, and eledoisin were presented. One entire session was devoted to substance P. At the closing session two motion pictures demonstrated the effect of the peptides on the circulation. The appendix of this volume contains the report of the international Committee on Nomenclature.