The riddle of the biochemical nature of drug dependence of the opiate type has stimulated many studies directed toward understanding the molecular basis of the action of opiates, and, particularly, the phenomena of tolerance, physical dependence, and drug-seeking behavior-phenomena exhibited by man and experimental animals exposed persistently to these drugs. The results of these studies provided a substantial body of information which has been published in the scientific and medical literature. The purely pharma cological responses in man and animals to the opiates have been described and...