The effects of 7-(4-[4-(2,3-dichlorophenyl)-1-piperazinyl]butyloxy)-3,4-dihydro-2 (1H)- quinolinone (OPC-14597), a derivative of the dopamine (DA) autoreceptor agonist 7-(3-[4-(2,3-dimethylphenyl)piperazinyl]propoxy)-2(1H)-quinolinone (OPC-4392), on DA receptors were biochemically and behaviorally studied and compared with those of OPC-4392. Both OPC-14597 and OPC-4392 inhibited reserpine- and gamma-butyrolactone (GBL)-induced increase in tyrosine hydroxylase activity in the mouse and rat brain. The effects of OPC-14597 were comparable to those of OPC-4392 and were completely antagonized by haloperidol. OPC-14597, unlike apomorphine, did not evoke postsynaptic DA receptor-stimulating behavioral signs such as hyperlocomotion in the reserpinized mice and contralateral rotation in rats with unilateral striatal 6-hydroxydopamine lesions. Both OPC-14597 and OPC-4392 inhibited such apomorphine-induced postsynaptic behavioral changes as stereotypy and hyperlocomotion in mice and rats and rotation in rats with unilateral striatal kainic acid lesions. The anti-apomorphine effects of OPC-14597 were about 30 to 140 times greater than those of OPC-4392 and were observed at doses that inhibit the increases in tyrosine hydroxylase activity. The affinities of OPC-14597 for 3H-spiperone-labeled D2 receptors in the rat frontal cortex, limbic forebrain and striatum were higher than those of OPC-4392. These results suggest that OPC-14597 is a unique antipsychotic drug candidate, being a DA autoreceptor agonist that has a stronger postsynaptic D2 receptor antagonistic activity than that of OPC-4392.