Humans have used opium extracts since antiquity, studied its purified active ingredient, morphine, for over a century, and directly demonstrated its receptors in brain only 6 years ago, and even more recently discovered the brain's own morphine. These endogenously produced opiate peptides have sparked an increase in information, creating a new area of neuroscience. Much excitement has greeted the opening of basic and clinical investigative corridors, influencing the course of research into addiction, pain, stress, and psychiatric illness. We review basic work concerning opiate receptors, and the endogenously produced opioid peptides, possible cellular mechanisms for addiction, involvement of endorphins in the action of antipsychotic drugs, the role of endorphins in pain modulation, and studies of endorphins in normal subjects and psychiatric patients.