Dopamine appears to be of less importance in the regulation of psychomotor functions than was previously thought. A central dopaminergic-glutamatergic balance may be important for both akinetic motor disorders and psychosis. In Parkinson's disease glutamate antagonists may counteract central glutamatergic hyperactivity and may be of value as anti-parkinsonian drugs. An increase of dopaminergic activity and/or a reduction of glutamatergic activity may contribute to the development of paranoid hallucinatory psychosis in schizophrenic patients and of pharmacotoxic psychosis in Parkinson's disease. Because of possibly severe side-effects of glutamatergic antagonists and agonists in the treatment of akinesia and psychosis, the development of partial glutamate agonists/antagonists could be an alternative strategy capable of producing antipsychotic or anti-kinetic effects with only mild adverse reaction.