Physiological systems in nonhuman primates can serve as excellent models of analogous physiological systems in humans. The purpose of the present research is to determine the type and magnitude of effects psychomotor stimulants, barbiturates, narcotic analgesics and narcotic antagonists can have on heart rate, systemic arterial blood pressure, body (rectal) temperature and behavior, what effects antagonists have when administered in combination with other drugs, and the effects of abrupt withdrawal of the drugs following a period of chronic administration. Squirrel monkeys and baboons will be surgically perpared with chronically indwelling arterial and venous catheters and rectal temperature probes to study the effects of acute and chronic drug administration on physiological activity, and parallel studies will investigate the effects of the drugs on behavior in the chimpanzee.