Inhibition of central dopamine functions appears to be a common basic property of antipsychotic drugs. The mesolimbic and nigrostriatal portions of the dopaminergic system are probably the main targets for the mental and the extrapyramidal actions, respectively, of these drugs. The fact that dopaminergic hyperfunction induced by amphetamines or dopa may lead to a disturbance mimicking paranoid schizophrenia lends further support for a key role of dopamine in mental functions. Although a primary disturbance in dopamine function in schizophrenia cannot be ruled out, the intimate relationship between dopaminergic and other neuronal systems must be emphasized. The possible involvement of other amine, amino acid, or peptide transmitters in schizophrenia cannot be disregarded.