Neuroimaging is a powerful and innovative tool for studying the pathology of psychiatric and neurological diseases and, more recently, for studying the drugs used in their treatment. Technological advances in imaging have made it possible to noninvasively extract information from the human brain regarding a drug's mechanism and site of action. Until now, our understanding of human brain pharmacology has depended primarily on indirect assessments or models derived from animal studies. However, the advent of multiple techniques for human brain imaging allows researchers to focus directly on human pharmacology and brain function. In this review article, our PET studies on histaminergic neuron system were presented as an example. We have developed and used the PET techniques for 10 years in order to examine the functions of histaminergic neurons in the living human brain. This review outlines available PET techniques and examines how these various methods have already been applied to the drug development process and neuropharmacology in the living human brain.