Nicotine is the major factor in the continuation of the smoking habit among humans. On December 2-4, 1985, under the sponsorship of the Tobacco and Health Research Institute in Lexington, Kentucky, leading scientists from around the world whose research efforts have focused on the role of nicotine in the tobacco habit participated in an International Symposium to provide the most comprehensive and ~xtensive coverage of this topic so far. The material discussed was in the forefront of man's knowledge about nicotine, and both lectures and question and answer sessions were stimulating and enlightening. This publication contains the manuscripts presented at the Symposium, along with an Overview prepared by selected individuals. Lecture and poster session topics are delineated more fully in the Overview. This volume is expected to serve as a definitive reference on nicotine as it relates to the tobacco habit. Symposium sessions were arranged under four headings: (1) behavioral effects of nicotine and nicotine~ependence in humans and animals, (2) neurohumoral regulation of neuroendocrine and cardiovascular function by nicotine, (3) neuropharmacology of nicotine, and (4) neurochemistry. This was the first assembly of this magnitude of scientists who had devoted years of research to nicotine and its effects. Indeed, it was a pleasure to have sponsored this important event. Dr. Lay ten Davis, Director Tobacco and Health Research Institute Cooper and Alumni Drives Lexington, KY 40546-0236 v ACKNOWLEDGMENTS The Editors of this volume express sincere appreciation to all of the contributors. Special acknowledgments are given to Ms.