The effects of cis- and trans-isomers of atypical neuroleptic carbidine on the synthesis of dopamine and its autoreceptor regulation in the striatum and nucleus accumbens of rats were examined by blocking decarboxylase of L-aromatic amino acids and interrupting the nerve impulse flow in the dopaminergic neurons. The striatal release and metabolism of dopamine were studied in vitro by employing K(+)-stimulated efflux from isolated striata and in vivo by the microdialysis in freely moving rats. Carbidine trans-isomer, unlike its cis-isomer, was shown to enhance the biosynthesis of dopamine via blockade of presynaptic autoreceptors presumably located on the dopaminergic terminals. The trans-isomer was found to be much more potent by affecting the neurochemical parameters of dopaminergic neurotransmission, which are essential for the drug to produce its antipsychotic effect.