The dopamine (DA) receptor regulating serotonin N-acetyltransferase (NAT) activity in chick retina was characterized pharmacologically. Intraocular (i.o.) administration of DA significantly decreased the nighttime NAT activity of chick retina. The effect of DA was antagonized by blockers of the D2 family of DA receptors, spiroperidol, YM-09151-2 and clozapine, and it was not affected by SCH23390, a selective antagonist of D1 DA receptor. Several agonists of D2 family of DA receptors given i.o. suppressed the nighttime NAT activity of the chick retina with quinpirole (D3/D4 receptor selective) and bromocriptine (D2/D3 receptor selective) being the most and the least potent drugs, respectively. The rank-order potency of antagonists of D2 family of DA receptors to block the inhibitory effect of quinpirole on the enzyme activity (with clozapine being relatively very potent, and (+)-butaclamol, raclopride and remoxipride-ineffective) match the characteristics of the D4 DA receptor. Moreover, although sulpiride effectively prevented the quinpirole-induced decline in the nighttime NAT activity of the chick retina, there was no marked stereoselectivity in its action. It is suggested that DA receptor regulating NAT activity in chick retina represents a D4-like subtype.