The antipsychotic actions and extra-pyramidal side-effects of neuroleptic drugs are strongly correlated with their ability to block central dopaminergic transmission. It is argued that the former are more closely related to actions on dopaminergic mechanisms in the "mesolimbic dopamine" system, and the latter to similar actions in the striatum. Although the amphetamine psychosis closely resembles paranoid schizophrenia and may be due to excess dopamine release, clinical, biochemical, and endocrine studies suggest that dopaminergic overactivity is not a necessary concomitant of schizophrenic illnesses. It is suggested that the primary defect in schizophrenia does not lie in the dopamine neuron. It remains to be excluded that the receptors, particularly in the mesolimbic dopamine areas, become supersensitive, or that there is a deficit in a system which normally acts in antiagonism to the to the mesolimbic dopamine system.