This review examines the history of discoveries that contributed to development of the dopamine hypothesis of schizophrenia. The origin of the hypothesis is traced to the recognition that neuroleptic drugs interfere with brain dopamine function. This insight was derived from two distinct lines of research. The first line originated from the discovery in 1956 that reserpine depletes brain serotonin. This finding resulted in a sequence of studies that led to the discovery that brain dopamine is involved in neuroleptic-induced extrapyramidal motor disturbances. The second line of research was aimed at determining the mechanism of action of psychomotor stimulants. This research produced evidence that stimulants directly or indirectly activate brain dopamine receptors. Because nonreserpine neuroleptics such as chlorpromazine block stimulant-induced movement, these findings suggested that neuroleptics were dopamine antagonists. Most previous accounts of the development of the dopamine hypothesis of schizophrenia emphasize the first line of research and ignore the second.