It is difficult to imagine an era in which there were no selective drugs for treating anxiety, depression, schizophrenia, and other mental ailments. Yet in a remarkably short time these drugs have come to occupy a position of prominence in medical practice throughout the world, and they now account for a major portion of all prescriptions. Most psychotropic drugs were discovered with little premeditation on the part of the inves~ tigator. The drugs simply worked, often with little rationale, and psychopharmacology has been for many years an empirical discipline in search of scientific underpinnings. In the past decade, a basic science of psychopharmacology has de veloped and grown rapidly. Though psychotropic drugs are exceedingly young as drugs in medical practice go, we probably know more about their various mechanisms of action than we know about most drugs in clinical use. Advances in understanding effects of psychopharmaceuticals on the brain have been so prodigious that a new research paradigm has evolved. Instead of being concerned solely with understanding how the drugs act, many researchers now employ psychotropic drugs as tools-often the most powerful ones-to elucidate brain function. Consequently, psychophar macology is central to neurobiology, which in turn has emerged as an important discipline, heir to the preeminent glamor of molecular biology.