This research is part of a program of study of how the behavioral effects of drugs depend upon the past and present control of behavior by environmental events and will deal particularly with procedures involving noxious stimuli. Both suppression and maintenance of behavior by schedules of presentation of noxious stimuli will be used. Dose- effect relationships will be established for representative drugs. Studies comparing the effects of drugs on behavior maintained by termination of a stimulus-shock complex and by presentation of food will be continued. The interrelations between these different schedule- controlled performances and changes in heart rate and blood pressure will also be studied. Patterns of behavior have been developed and maintained in the squirrel monkey under conditions in which responses produce noxious stimuli. The importance of experimental history, schedule of presentation of noxious stimuli, and schedule parameter values will be studied. Several different schedules under which responding is maintained by response-produced noxious stimuli will be used to study the effects of representative drugs on this behavior.