&NA;Aripiprazole (OPC 14597) is a quinolinone derivative under development as a potential antipsychotic agent. It is currently undergoing phase III clinical trials with Otsuka in Japan and the US.Aripiprazole is thought to act as a presynaptic dopamine D2 autoreceptor agonist and as a postsynaptic dopamine D2 receptor antagonist. The pharmacological profile of aripiprazole suggests that it may be effective against both the positive and negative symptoms of schizophrenia.Aripiprazole is a quinolinone derivative of OPC 4392. Both of these compounds exhibit unusual functional profiles, with dual agonist/antagonist activity at dopamine D2receptors. Whereas the postsynaptic antagonist actions of OPC 4392 are observed at much higher doses than those that elicit presynaptic agonism, these opposing effects occur at equivalent doses of aripiprazole. Clinical testing of OPC 4392 was terminated because of some exacerbation of positive symptoms. Early clinical testing of aripiprazole, however, suggest efficacy against positive and negative symptoms of schizophrenia, with little induction of extrapyramidal symptoms.